matrix interaction in magnetic hybrid materials with application for

Transcription

Program of the 2nd Colloquium of DFG Priority Program 1681
Field controlled particle matrix interactions: synthesis, multiscale
modelling and application of magnetic hybrid materials
Benediktbeuern, September 29th – October 1st 2014
Monday, September 29th
14:00
Opening
14:30
Material Synthesis & Characterization
14:30
M. U. Witt, S. Backes, R. v. Klitzing
Multifunctional Microgel Particles
14:50
M. Zhou, T. Liebert, A. Dellith, S. Dutz, T. Heinze, R. Müller
Hybrids from magnetic nanoparticles and meltable
biopolymer for remote controlled release system
10
15:10
I. Appel, K. May, A. Eremin, A. Nack, J. Wagner, R. Stannarius,
S. Behrens
Synthesis and characterization of magnetic nanoparticles and
their integration into liquid crystal hybrids
12
15:30
C. Schopphoven, A. Tschöpe
Field Induced Rotation of Ferromagnetic Nanorods in an
Elastic Matrix
20
15:50
Coffee Break & Posters
16:20
Theory
18:00
8
16:20
R. Weeber, Ch. Holm
Deformation mechanisms of magnetic gels studied by
computer simulations
22
16:40
S.D. Peroukidis, S.H.L. Klapp
Molecular simulations of liquid crystalline ferrofluids
24
17:00
H.R. Brand, H. Pleiner
Macroscopic behavior of ferronematic gels and elastomers
28
17:20
A. Attaran, J. Brummund, T. Wallmersperger
Development of a magneto-mechanical continuum model for
ferrogels
29
17:40
C. Spieler, M. Kästner
XFEM model generation and magneto-mechanical simulation
of MRE
30
Postersession
2nd Colloquium SPP 1681
1
Tuesday, September 30th
14:00
Mountain and Alternative Tour
Mountain Tour from Pessenbach to Jachenau and
Alternative Tour to cloister Ettal and from there by bus
to Jachenau
Mountain Talks
16:30
19:00
2
A. Eremin, K. May, R. Stannarius, P. K. Challa, J. Gleeson,
A. Jákli, I. Appel, S. Behrens, S. Klein
On the way to multiferroic materials: Magnetic field-induced
orientational transfer in two-component colloidal suspensions
of anisometric particles
16
P. Cremer, G. Pessot, M. Tarama, B. ten Hagen, K. Popowa,
A. Kaiser, E. Allahyarov, H. Löwen, A. M. Menzel
Mesoscopic modeling of ferrogels: from tunable relaxation
dynamics to nonlinear stress-strain behavior
26
M. von der Lühe, A. Weidner, U. Günther, C. Gräfe, S. Dutz,
F. H. Schacher
Fe3O4@Polydehydroalanine Hybrid Particles
54
Experiments & Rheology
16:30
J. Landers, L. Roeder, A. M. Schmidt, H. Wende
Comparative study of nanoparticle motion by Mössbauer
spectroscopy and AC-susceptometry
32
16:50
H. Remmer, C. Kuhlmann, J. Dieckhoff, A. Lak, E. Roeben,
A. M. Schmidt, F. Ludwig
Dynamic magnetic investigations of the particle-matrix
interaction of magnetic hybrid materials
34
17:10
S. Metzke, J. Seliger, S. Prévost, M. Gradzielski
Magnetic and temperature-responsive ferrogels with low
molecular weight gelators
36
17:30
S. Huang, G. K. Auernhammer
Magneto-elastic behavior of super-paramagnetic particle
chains in a soft gel
38
Colloquium Dinner
Wednesday, October 1st
8:45
8:45
E. Roeben, L. Roeder, S. Teusch, M. Dörfer, L. Kibkalo,
M. Effertz, U. K. Deiters, A. M. Schmidt
Magnetic Particle Nanorheology
40
9:05
A. Nack, J. Seifert, J. Wagner
Investigation of rheological and dynamic properties of
composites consisting of viscous hydrogels and anisotropic
hematite particles
42
9:25
M. Schümann, S. Odenbach
Effects of the magnetization on the particle structure of
magnetorheological elastomers
46
9:45
Coffee Break & Posters
10:15
Applications
12:35
10:15
I. Slabu, A. Roeth, T. Schmitz-Rode, M. Baumann, D. Eberbeck,
L. Trahms
Kinetic analysis of subsequent internalization of
magnetoliposomes in two different pancreatic cancer cell
types
48
10:35
R.P. Friedrich, P. Tripal, J. Zaloga, J. Nowak, S. Odenbach,
M. Liebl, L. Trahms, S. Lyer, C. Alexiou
Magnetic Hybrid Materials for the Regenerative Medicine:
Synthesis, Simulation, Application and toxicological
Investigations
50
10:55
C. Gräfe, F. Wiekhorst, R. Müller, A. Hochhaus, F. von Eggeling,
J.H. Clement
Passage of SPIONs through cell layers
52
11:15
E. I. Wisotzki, M. Hennes, M. Zink, S. G. Mayr
Radiation optimized hydrogels and plasma-synthesized
nanoparticles for magnetically-controllable degradable
bioactuators
56
11:35
I. Zeidis, V. Böhm, T. Kaufhold, K. Zimmermann, V.A. Naletova
Actuator systems based on a controlled particle-matrix
interaction in magnetic hybrid materials with application for
locomotion and manipulation
58
11:55
M. Krautz, M. Schrödner, J. Popp, A. Waske, J. Eckert
Experimental strategies towards porous soft magnetic
composites
60
12:15
J. Popp, M. Schrödner
Semi-industrial synthesis, characterization and shaping of
magnetosensitive elastomers focued on compliant sensor
manipulator applications
62
Closing
3
Abstracts
Material Synthesis & Characterization
8
M. Zhou, T. Liebert, A. Dellith, S. Dutz,
T. Heinze, R. Müller
Hybrids from magnetic nanoparticles and
meltable bi-opolymer for remote
controlled release system
10
I. Appel, K. May, A. Eremin, A. Nack,
J. Wagner, R. Stannarius, S. Behrens
Synthesis and characterization of
magnetic nanoparticles and their
integration into liquid crystal hybrids
12
Ch. Klopp and R. Stannarius
Measurement of the torque on ferrofluid
samples in rotating magnetic fields
14
A. Eremin, K. May, R. Stannarius,
P. K. Challa, J. Gleeson, A. Jákli, I. Appel,
S. Behrens, S. Klein
On the way to multiferroic materials:
Magnetic field-induced orientational
transfer in two-component colloidal
suspensions of anisometric particles
16
K. Birster, A. Tschöpe, R. Birringer
Oscillatory dynamics of ferromagnetic
nanorods in gelatin solutions
18
C. Schopphoven, A. Tschöpe
Field Induced Rotation of Ferromagnetic
Nanorods in an Elastic Matrix
20
R. Weeber, Ch. Holm
Deformation mechanisms of magnetic
gels studied by computer simulations
22
S.D. Peroukidis, S.H.L. Klapp
Molecular simulations of liquid crystalline
ferrofluids
24
P. Cremer, G. Pessot, M. Tarama,
B. ten Hagen, K. Popowa, A. Kaiser,
E. Allahyarov, H. Löwen, A. M. Menzel
Mesoscopic modeling of ferrogels: from
tunable relaxation dynamics to nonlinear
stress-strain behavior
26
H.R. Brand, H. Pleiner
Macroscopic behavior of ferronematic
gels and elastomers
28
A. Attaran, J. Brummund, T. Wallmersperger
Development of a magneto-mechanical
continuum model for ferrogels
29
XFEM model generation and magnetomechanical simulation of MRE
30
J. Landers, L. Roeder, A. M. Schmidt,
H. Wende
Comparative study of nanoparticle
motion by Mössbauer spectroscopy and
AC-susceptometry
32
H. Remmer, C. Kuhlmann, J. Dieckhoff,
A. Lak, E. Roeben, A. M. Schmidt, F. Ludwig
Dynamic magnetic investigations of the
particle-matrix interaction of magnetic
hybrid materials
34
S. Metzke, J. Seliger, S. Prévost,
M. Gradzielski
Magnetic and temperature-responsive
ferrogels with low molecular weight
gelators
36
Theory
6
Magneto-elastic behavior of superparamagnetic particle chains in a soft gel
38
E. Roeben, L. Roeder, S. Teusch, M. Dörfer,
L. Kibkalo, M. Effertz, U. K. Deiters,
A. M. Schmidt
40
A. Nack, J. Seifert, J. Wagner
Investigation of rheological and dynamic
properties of composites consisting of
viscous hydrogels and anisotropic
hematite particles
42
C. Passow, B. ten Hagen, H. Löwen,
J. Wagner
Depolarized light scattering from
anisotropic particles: the influence of the
particle shape on the field
autocorrelation function
44
Effects of the magnetization on the
particle structure of magnetorheological
elastomers
46
I. Slabu, A. Roeth, T. Schmitz-Rode,
M. Baumann, D. Eberbeck, L. Trahms
Kinetic analysis of subsequent
internalization of magnetoliposomes in
two different pancreatic can-cer cell
types
48
R.P. Friedrich, P. Tripal, J. Zaloga, J. Nowak,
S. Odenbach, M. Liebl, L. Trahms, S. Lyer,
C. Alexiou
Magnetic Hybrid Materials for the
Regenerative Medicine: Synthesis,
Simulation, Application and toxicological
Investigations
50
C. Gräfe, F. Wiekhorst, R. Müller,
A. Hochhaus, F. von Eggeling, J.H. Clement
52
M. von der Lühe, A. Weidner, U. Günther,
C. Gräfe, S. Dutz, F. H. Schacher
Fe3O4@Polydehydroalanine Hybrid
Particles
54
E. I. Wisotzki, M. Hennes, M. Zink, S. G. Mayr
Radiation optimized hydrogels and
plasma-synthesized nanoparticles for
magnetically-controllable degradable
bioactuators
56
I. Zeidis, V. Böhm, T. Kaufhold,
K. Zimmermann,
58
V.A. Naletova
Actuator systems based on a controlled
particle-matrix interaction in magnetic
hybrid materials with application for
locomotion and manipulation
M. Krautz, M. Schrödner, J. Popp, A. Waske,
J. Eckert
Experimental strategies towards porous
soft magnetic composites
60
J. Popp, M. Schrödner
Semi-industrial synthesis,
characterization and shaping of
magnetosensitive elastomers focued on
compliant sensor manipulator
applications
62
Applications
7
Technische Universität Berlin, Straße des 17. Juni 124, 14109 Berlin, Germany
The combination of magnetic nanoparticles (MNP) and an N-isopropylacrylamide
(NIPAM) based hydrogel is investigated.
Due to the incubation of the MNP into the
PNIPAM the response to outer stimuli
changes. The gel is still temperatureand pH-responsive and gains an additional response to magnetic fields. This
gives the opportunity to get novel actuatoric materials
Hydrogel Synthesis
The hydrogel synthesis was performed in
two ways. The first one is called batch
method and the second one is called
feeding method.
The batch method is quite intuitive. The
first synthesis is performed in a heated
bath
consisting
of
all
ingredients
(PNIPAM, BIS1, AA2, AAPH3). The reaction conditions are chosen to be 80°C
and under nitrogen atmosphere.
In the feeding reaction the reactants are
fed into the bath with a syringe pump.
Acciaro et al. [1] used a slightly different
approach in their feeding reaction. They
already had some initial concentration of
the reactants in the bath to compensate
the initial divergence in the consumption
rate of NIPAM and BIS.
The growth of the hydrogel is shown in
Fig.1.
Magnetic Nanoparticles
The MNP so far have been provided by
other groups of the SPP1681.
The magnetite/maghemite particles are
synthesized by Ingo Appel4 and the cobalt ferrite particles by Eric Röben5.
Hybrid Preparation
The hybrids are prepared by simple mixing and subsequent sonicating of the
hydrogel and MNP. The hybrids can be
seen in Fig.2.
Fig. 2: TEM picture of hybrid particles
PNIPAM/cobalt ferrite.
Mechanical properties at surfaces
Fig. 1: The growth of the gel particle is
depicted by plotting the radius over the
reaction time.
1
N,N‘-Methylenebisacrylamide (crosslinker)
AllyAmine (comonomer)
3
2,2‘-Azobis(2-methylpropionamidine)-dihydrochloride (radical
initiator)
To study the actuatoric behavior of ferrogels, they are deposited on a surface
(Si-Wafer) via spincoating. The gel particle dimensions against both air and liquid
(water) can be determined with an
Atomic Force Microscope (AFM) (see
Fig.3).
2
8
4
Institut fuer Katalyseforschung und –technologie, Hermannvon-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen
5
Universität Köln Institut für Physikalische Chemie, Luxemburger Str. 116, D-50939 Köln
Variable
Field
Module
2
(VFM2)extension for an MFP-3D AFM (Asylum
Research). The applied field could be
varied up to 0.3 T. First results show an
increase of particle height and volume
with an increasing magnetic field,
whereas the area of the particle changes
only slightly (see Fig.6). This effect is
currently under investigation.
Fig. 3: AFM-micrograph of a PNIPAM/
cobalt ferrite hybrid particle against air.
Pure PNIPAM gel particles are known to
show a temperature responsive behavior.
They exhibit a volume phase transition
temperature (VPTT) above which they
collapse. Measurements with the hybrid
ferrogel particles containing MNP also
show a temperature dependence, so this
behavior is preserved when adding MNP
(see Fig.4&5).
Fig. 6: Dependence of particle dimensions on the applied magnetic field parallel to the surface.
Next Steps
Fig. 4: AFM-scan of ferrogel particles in
water at (a) 20°C (swollen state) and (b)
55°C (shrunken).
Further steps are the optimization of
MNP embedding (high uptake of MNP
versus stimuli sensitivity) and investigation of magnetization and mechanical
properties.
Acknowledgment
The work is funded by the DFG within the
SPP1681.
References
[1] R. Acciaro, I. Varga, ACS 2011, 12, 79177925
Fig. 5: Temperature dependence of ferrogel particles during one heatingcooling-cycle from 20°C-55°C.
Measurements of ferrogel particles in an
external magnetic field parallel to the
surface have been carried out using the
9
Hybrids from magnetic nanoparticles and meltable
biopolymer for remote controlled release system
M. Zhou1, T. Liebert1, A. Dellith2, S. Dutz3, T. Heinze1, R. Müller2
1
Institute of Organic Chemistry and Macromolecular Chemistry, Friedrich Schiller University of Jena, Germany.
2
Leibniz-Institute of Photonic Technology (IPHT), Jena, Germany
3
Institute of Biomedical Engineering and Informatics, TU Ilmenau, Germany
The aim of this project is to develop a
biocompatible hybrid material from a
defined meltable polymer and functional
nanoparticles, which can be softened
under an induced alternating magnetic
field (AMF) and allows in that way a release of active pharmaceutical ingredients (API). This could be a suitable alternative for swellable hydrogel composites
embedded with magnetic particles as
remote controlled biomaterial [1].
The final goal of the project is the elucidation of the release mechanism from
such a new system on microscopic scale.
Therefore, comparison of the melting
behavior and the resulting viscosity
caused by intrinsic heating with a conventional
external
(thermoelectrical)
heating process will be studied. For this
purpose surface plasmon effect of gold
nanoparticles (as a model for the AMFheating) and optical tracing of single
magnetic beads under static magnetic
field can be exploited.
In a first step we have synthesized different meltable dextran esters with fatty
acids [2] and developed preparation procedures for the hybrid materials. The
melting range of the dextran esters can
be adjusted by degree of substitution
(DS), molecular weight of dextran and
chain length of fatty acid. Magnetite nanoparticles (MNP) were obtained by wet
chemical process in alkaline media [3]
and then the product was coated with
oleic acid in order to be stabilized and to
have a hydrophobic surface property.
The dextran esters and the MNP were
analyzed by numerous methods like
NMR, FTIR, DSC, TGA, rheometer (Fig.
1), dilatometry, hot table microscope (for
polymers) and DLS and vibrating sample
magnetometry (for MNP).
10
Fig.1: Temperature dependent viscosity
and dilatometric softening temperatures of
two different polymers
Uncoated MNP show a coercivity HC of
3.1 kA/m and a saturation magnetization
MS of 74.8 Am2/kg, oleic acid coated MNP
a HC of 2.5 kA/m and MS of 68.8 Am2/kg.
Magnetic nanocomposites with different
concentrations between 0.06 and 2.2
wt% were obtained by following steps:
Firstly mixing of dextran ester and coated MNP in an organic solvent (e.g. toluene or THF) and secondly homogenizing
of the suspension by ultrasonic treatment; finally the nanocomposites were
dried and precipitated out from the suspension. The nanocomposites were coated on object glasses by applicator into
20 x 30 mm2 square with thickness of 50
µm and 5 µm. The morphology and distribution of MNP in the polymer was discovered by scanning electron microscope
(SEM) and optical microscope (Fig.2).
The MNPs in range of 100 nm and 1 µm
are distributed uniformly in the polymer
matrix (Fig.2). Some agglomerates are
formed during the synthesis. SEM picture
shows the particles are also well distributed in the cross sectional direction (not
shown). The MNPs are interlocked in the
polymer matrix. Increasing hysteresis
parameters (Hc, remanence ratio Mr/Ms)
with decreasing particle content suggest
a decreasing magnetic interaction, i.e. a
better separation of particles on microscopic scale [4] (Fig.3). The particle content was calculated from magnetization
values.
effect of waste heat by the generator
measured on a layer without MNP are
335, 63 and 4.5 mK/s.
Fig.4: Heating curve of a composite in AMF
Fig.2: SEM (left) and optical image (right)
of MNP in dextran ester polymer
Fig. 5: IR images of a magnetic composite
layer in AMF test after 60 and 300s
Fig.3. Hysteresis parameters of composites
with different particle content.
The specific absorption rate of the
compsite (2.2%) was determined with a
fiberoptical sensor on a bulk shaped
sample (Fig.4) what was subjected to an
AMF (20 kA/m, 400 KHz). The object
glasses were placed in the middle of a
coil in air at room temperature. The surface temperature was recorded by a IR
camera 20 s before and 5 min after the
magnetic induction (Fig.5). Keep in mind
there are no Brownian losses.
The internal melting behaviour of the
composite depends on type of polymer,
MNP content and geometry of the sample. High DS dextran palmitate and dextran myristate were chosen for fabrication of magnetic hybrid material because
they have a melting range nearly above
the human body temperature.
The dependence of the heating on the
geometry was tested with a thickness of
the polymer layers of 600, 50 and 5 µm,
respectively, and 2.2% MNP content. The
corresponding heating rates after the
This is a first proof of concept for the
defined melting of biocompatible polymers with MNPs.
Outlook
In the second year of the program, our
focus will be on the microviscosity study,
release experiments and biocompability
test.
References
[1]
[2]
[3]
[4]
N. S. Satarka, et al, Acta Biomater. 4, 11-16,
2008; T. Hoare, et al, Nano Lett. 11, 13951400, 2011
T. Liebert et al, Biomacromolecule 12, 31073113, 2011
R. Müller, et al.,J. Magn. Magn. Mater. 323,
1223–1227, 2011
S. Dutz et al., J. Nano Electr. Phys. 4/2 2012,
02010
Acknowledgments
This Project is funded by DFG Priority
Program (SPP) 1681. We thank D. Borin
(TU Dresden) for rheological measurements and I. Hilger (IDIR Jena) for
providing the IR camera.
11
Synthesis and characterization of magnetic nanoparticles and their integration into liquid crystal
hybrids
I. Appel1, K. May2, A. Eremin2, A. Nack3, J. Wagner3, R. Stannarius2, and S. Behrens1
1
Institut für Katalyseforschung und-technologie; Karlsruher Institut für Technologie (KIT), Postfach 3640,
76021 Karlsruhe
2
Abteilung Nichtlineare Phänomene; Otto-von-Guericke-Universität Magdeburg, Universitätsplatz 2, 39106 Magdeburg
3
Institut für Chemie; Universität Rostock, Dr.-Lorenz-Weg 1, 18059 Rostock
Liquid crystalline (LC) materials combine
the fluidity of liquids and the anisotropic
properties of crystals that give rise to
their birefringent character. The more
aligned the mesogenic molecules are, the
higher is the macroscopic birefringence.
The alignment can be controlled by external fields, an effect which is utilized in
LC displays. The embedding of magnetic
nanoparticles and ferrofluids increases
the sensitivity of LC systems to small
magnetic fields. This effect was first described theoretically by Brochard and de
Gennes in 1970 [1]. Such suspensions
were prepared experimentally by various
groups [2-4]. However, these systems in
general proved to be unstable and suffered from segregation and aggregation.
The synthesis of magnetic LC systems
with long-term stability and particle concentrations beyond 1 wt.-% still remains
a challenge, and many of these complex
systems are not yet fully understood.
In our approach, we have initially synthesized a “pool” of magnetic particles
where parameters like size, shape, composition, and surface functionality can be
controlled and systematically varied. By
integration of these different magnetic
nanoparticles in LC matrices we want to
contribute to a better comprehension of
the particle matrix interactions, and we
want to be able to control these interactions.
Monodisperse iron oxide spheres, 5.5
(Figure 1a) and 10 nm in diameter,
resp., were synthesized by thermal decomposition of iron(III)oleate [5]. 17
nm-sized iron oxide nanospheres (Figure
1c) with a narrow size distribution or iron
oxide nanorods with approximately 25
nm length and 5 nm diameter (Figure
12
1d) were obtained by thermal decomposition of iron pentacarbonyl, depending
on the exact reaction conditions [6]. All
oleate-coated nanoparticles yielded stable colloidal solutions in cyclohexane that
revealed, in case of spherical particles,
superparamagnetic properties.
Starting from the suspensions in cyclohexane, the nanoparticles were dispersible in water after oxidative cleavage of
the oleate´s double bond [7] (Figure
1b). However, after this change of surface functionality, the particles tended to
aggregate, yet they were fully redispersible after agitation.
Hematite Spindles dispersed in water
with l ~ 250 nm and an aspect ratio of 4
were used as received.
The nanoparticles were characterized by
DLS, ICP-OES, SEM, TEM, AGM, and
XRD.
a
b
c
d
Figure 1: Iron oxide nanoparticles of different sizes and geometries: TEM images
of spherical particles (d = 5.5 nm) in a)
cyclohexane and b) water; c) TEM image
of spherical particles (d ~ 17 nm) in cyclohexane; d) SEM image of nanorods (l
~ 25 nm, d ~ 5 nm).
Three types of LC systems have been
examined and were used as matrices for
the synthesized nanoparticles:
(i) thermotropic LCs
(ii) thermotropic ionic liquid crystals
(iii) one lyotropic system (potassium
laurate, water and 1-decanol).
In this context, both commercially available and tailored, self-synthesized systems were investigated. Special efforts
have been devoted to the synthesis of LC
molecules equipped with specific functionalities for nanoparticle binding.
All types of nanoparticles in cyclohexane
could be dispersed in the lyotropic system (iii) with a concentration of 0.01 wt.% Fe and were stable at least for several
days. Nanoparticles suspended in water,
including hematite spindles, could not
yet be stabilized in the lyotropic LC.
Oleate-coated nanoparticles were suspended
in
MBBA
(N-(4-Methoxybenzylidene)-4-butylaniline) to yield homogeneous suspensions (i), which displayed a nematic phase at room temperature and were stable during several
days for concentrations below 0.1 wt.-%
Fe. Preliminary experiments with (ii) resulted in inhomogeneous hybrid materials where the nanoparticles readily aggregated and segregated from the LC
phase.
The LC systems were characterized by
NMR and IR spectroscopy, DSC, and optical polarized microscopy.
Currently, the magnetic hybrid LC materials are investigated by birefringence
measurements as a function of magnetic
field strength.
Our initial results show that sets of small
magnetic nanoparticles with different
sizes and shapes can be integrated in LC
systems in low concentrations. In future
experiments, special attention will be
devoted to tailor the surface chemistry of
the nanoparticles, for affording higher
particle concentrations and increased
colloidal stability of the hybrid systems.
Acknowledgements
The financial support by the DFG via
SPP1681 is gratefully acknowledged.
References
[1]
Brochard, F.; de Gennes, P. G., Journal de
Physique 1970, 31 (7), 691-708.
[2]
Chen, S.-H.; Chiang, S. H., Molecular
Crystals and Liquid Crystals 1987, 144 (5), 359370.
[3]
Hayes, C. F., Molecular Crystals and Liquid
Crystals 1976, 36 (3-4), 245-253.
[4]
Liebert, L.; Martinet, A., Journal de Physique Lettres 1979, 40 (15), 363-368.
[5]
Park, J.; An, K.; Hwang, Y.; Park, J. G.;
Noh, H. J.; Kim, J. Y.; Park, J. H.; Hwang, N. M.;
Hyeon, T., Nat Mater 2004, 3 (12), 891-895.
[6]
Sun, H.; Chen, B.; Jiao, X.; Jiang, Z.; Qin,
Z.; Chen, D., The Journal of Physical Chemistry C
2012, 116 (9), 5476-5481.
[7]
Si, J.-C.; Xing, Y.; Peng, M.-L.; Zhang, C.;
Buske, N.; Chen, C.; Cui, Y.-L., CrystEngComm
2014, 16 (4), 512-516.
13
Measurement of the torque on ferrofluid samples
in rotating magnetic fields
Ch. Klopp and R. Stannarius
Abteilung Nichtlineare Phänomene; Otto-von-Guericke-Universität, Universitätsplatz 2, 39106 Magdeburg
We study the torque of rotating magnetic
fields on ferrofluids in spherical containers. Magnetic field strengths are chosen
in the range up to 20 kA/m, rotation frequencies are in the range from 0 to 100
Hz. Commercial ferrofluids are filled in
glass containers (diameters of the order
of 2 cm) suspended by a thin glass fiber.
From the distortion angle of the fiber we
find the magnetic torque in the stationary state and determine frequency and
field strength dependencies. The interpretation of the results is still open.
The experiment is sketched in Figure 1.
Two coaxial coil pairs adjusted perpendicular to each other are used to produce
sinusoidal magnetic fields in the horizontal plane with a mutual phase shift of 90°
and identical amplitudes. This generates
a rotating magnetic field at the position
of the sample sphere. The currents necessary for the coils (amplitudes between
0 and 4.5 A) are supplied by a Kenwood
Power 2-Channel Amplifier KAC 7204.
The ferrofluid sample is placed in the
center at the intersection of the coil axes. We attempt to create magnetic fields
as uniform as possible within the sample
volume. For geometrical reasons, Helmholtz coil pairs of same sizes could not be
placed, so that the actual coil distance of
each pair is roughly equal to the coil diameter. The magnetic field is consequently not exactly uniform, but measurements as well as analytical calculations show that the field inhomogeneity
across the sample volume is less than 3
%. Hall probes are used to monitor the
magnetic fields to verify the uniformly
rotating field of constant amplitude.
The samples are ferrofluid filled glass
spheres of roughly 2 cm diameter, suspended by a 58,3 cm long glass fiber.
This fiber is fixed rigidly at its upper end.
When a magnetic torque acts on the
sample, the fiber twists and creates an
elastic counter-torque. A camera observes the rotation angle of the sample.
14
Knowing the restoring torque of the fiber
as a function of the distortion angle, one
can calculate the magnetic torque on the
sample from the torque balance.
Figure 1: Four coils around the spherical
sample container (which is shown here
outside the setup) generate the rotating
magnetic fields. The field components
are measured by Hall probes. A glass
fiber (approx. 58 cm long) is employed
to suspend the sample. The torsion angle
is determined by a camera observing
marks on a disk fixed to the sample.
The torsional constant D is measured for
each sample/glass fiber separately from
the angular frequency  = (D/J)1/2 of
small oscillations of the sample about the
equilibrium angle in absence of magnetic
fields, and known moment of inertia J of
the sample. Oscillation periods 2/ are
between 5 s and 8 s, sample masses
between 6 g and 10 g, moments of inertia from 2.510-7 kgm2 to 510-7 kgm2,
and corresponding torsional constants D
of the order of 310-7 kgm2s-2. This allows
to determine torques N = D of the order
of 10-7 Nm with an accuracy of a few
nNm from the torsion angle of the glass
fiber. In the experiments, we first mark
the equilibrium of the torsion pendulum
in zero field, then switch on the rotating
magnetic field and wait for establishment
of the torque balance (the time is mainly
determined by the eigenfrequency of the
pendulum). The torque N on the sample
at the given magnetic field strength and
frequency is found from the distortion
angle . The setup is essentially similar
to the one used in an earlier study of
ferrofluids under superimposed nonrotating magnetic fields [1] to confirm
and quantify a theoretically predicted
thermal ratchet effect [2].
All investigated ferrofluid samples were
chosen from the commercially available
APG series (Ferrotec).
The magnetic field H exerts a torque on
the individual ferrofluid particles. When
the magnetic interaction energy is comparable to or larger than the thermal
energy, the particles are orientationally
aligned towards the momentary field
direction. In sufficiently slowly rotating
fields, the particles follow the rotation of
the field synchronously, but owing to the
finite relaxation time (primarily, viscous
friction), there is a certain phase lag, a
mismatch angle
between the magnetic
moments and the rotating field. Magnetic
torques on the particles are balanced by
viscous drag of a concentric shear flow
inside the spherical sample container,
and this shear flow in turn acts on the
glass container. There, the torque is
compensated by the twisted torsion wire.
In a preliminary model, we assumed that
the phase lag angles  should increase
with increasing rotation velocity of the
field as long as the particles (i. e. their
magnetizations) follow the field synchronously. Thus, the torque should increase
with the angular frequency  until some
limiting c is reached, where the magnetic moments cannot follow the field
any more (the synchronous rotation becomes unstable for . Then, on increasing  the mean torque should vanish. Since c will depend upon particle
diameters and magnetic moments, we
expect a gradual decrease of N with
higher rotation rates in the polydisperse
samples. The critical c should increase
linearly with H. There are some analogies
to early work of Brochard et al. [3,4] on
anisotropic fluids (nematics) in rotating
magnetic fields. There, such synchronous
and asynchronous regimes were clearly
identified. Figures 2 and 3 show that the
situation is very different, even counterintuitive, in the ferrofluid experiment. A
suitable model is in preparation.
Figure 3: Frequency dependence of the
torque (per 7.31 g) on APG O 57 for different field strengths. A pronounced
maximum is found at /2 around 30 Hz.
Astonishingly, this maximum shifts to
lower frequencies in higher fields.
Figure 2: Magnetic torque N on a 7.31 g
sample of APG O 57 as a function of the
magnetic field amplitude H for different
rotation frequencies of the field. All
curves show a slightly nonlinear increase
of N with H, until saturation is reached at
around 15 kA/m (approx. 19 mT).
The Authors acknowledge T. Trittel and
T. John for valuable contributions.
References
[1] T. John and R. Stannarius, Phys. Rev. E 80,
050104(R) (2004).
[2] A. Engel, H. W. Müller, P. Reimann, and A.
Jung, Phys. Rev. Lett. 90, 060602 (2003).
[3] F. Brochard, J. Physique (Lett.) 35, L19 (1974).
[4] F. Brochard, L. Leger, and R. B. Meyer, J. Physique 36 Coll. C1 209 (1974).
15
On the way to multiferroic materials: Magnetic
field-induced orientational transfer in twocomponent colloidal suspensions of anisometric
particles.
A. Eremin1, K. May1, R. Stannarius1, P. K. Challa2, J. Gleeson2,
A. Jákli2, I. Appel3, S. Behrens3 S. Klein4
Otto-von-Guericke Universität, FNW/IEP/ANP, 39106 Magdeburg, Germany
Liquid Crystal Institute, Kent State University, Kent, OH 44242-0001, USA
3
Institute of Catalysis Research and Technology (IKFT) Hermann-von-Helmholtz-Platz 1 D-76344 EggensteinLeopoldshafen
4
HP Laboratories, Long Down Avenue, Stoke Gifford, Bristol BS34 8QZ, UK
1
2
Multiferroics are distinguished by the
presence of two or more primary ferroic
order parameters such as spontaneous
polarisation or magnetisation or elastic
strain. Such materials have potential in
various applications such as sensors,
actuators, tunable microwave devices,
phase shifters and oscillators. Development of soft composite materials based
on liquid crystals and colloids is particularly important. Colloidal suspensions of
anisometric particles have become an
attractive field of study for their ability to
form structured phases (such as nematics and smectics) and their complex behaviour in electric fields. Such responsive anisotropic colloids have a great
potential for development of smart functional materials. Long-range interparticle
interactions in nonpolar suspensions,
resulting from weakly screened electrostatic forces, may strongly affect the
particle dynamics and behaviour in electric fields.
In our research we study rod-shaped
anisometric colloidal pigment particles
dispersed in dodecane. The submicrometre size particles have small
slenderness ratio of approx. 4:1 (Fig.
1). These dispersions belong to nonpolar
colloids and it is distinguished by a formation of orientationally ordered state at
a volume fraction as low as 0.17. Below
this limit, the dispersions show a very
high response of the orientational order
to an external electric field and mechanical shearing. In our previous studies, we
demonstrated a strong field-induced birefringence (Fig. 2) and electro-optical
switching which have been studied using
depolarising microscopy and X-ray [1].
Figure 2. Switching in a 10 m ITO cell
with in-plane electrodes under crossed
polarizers (vertical and horisontal). The
electric field is aligned along the diagonal
(Upp = 12 V, f = 100Hz).
Figure 1 SEM image of the investigated
pigment particles.
16
Various kinds of patterns and electrokinetic phenomena have been studied in
this system under the action of electric
fields [2]. These patterns result from
phases separation into particle rich and
particle poor regions. Using electrospinning technique, we could produce coloured woven fiber mats with exhibit piezoelectric behavior [3].
The pure dispersions of the pigment particles are diamagnetic. They show a very
weak magneto-optical response, which
was observed in very strong magnetic
field up to 25T. One way to enhance the
magneto-optical response is to disperse
magnetic particles in the pigment sus-
pensions. In 1984, Lekkerkerker et al
developed a theory, which showed that
two-component hard rod dispersions
with one magnetic and one nonmagnetic component exhibit a stabilised
anisotropic phase even at a small concentration of the magnetic particles.
Such materials demonstrated in Refs. [46], have an enhanced magneto-optical
response.
In this presentation, we show an enhancement of the magneto-optical response in the colloidal pigment suspensions mixed with commercially available
ferrofluid APG935. The mixture shows
good stability and a field-induced birefringence already in fields as low as few
hundred Tesla (Fig. 3). Similar behaviour
we found in dispersions of spherical
magnetite particles with diameter of 17
nm.
Acknowledgments
This
research
was
supported
by
Deutsche Forschungsgemeinschaft (Project STA 425/28), European COST Action
(IC1208), DAAD Grant 56038231.
References
[1]
[2]
[3]
[4]
[5]
[6]
A. Eremin et al, Adv. Funct. Mater., 21, 402,
(2011).
K. May, R. Stannarius, S. Klein, and A. Eremin, Langmuir 30, 7070 (2014).
K. May et al., RSC Advances, (in press)
H.N.W. Lekkerkerker et al, J. Chem.
Phys. 80, 3427 (1984)
K. Slyusarenko et al, Phil. Trans. R. Soc.
Lond. A, 371, 1988, 20120250, (2013).
S. Kredentser et al, Soft Matter, 9, 20, 5061,
(2003)
Figure 3. (top) Dependence of birefringence on the magnetic field in a 5
wt% pigment suspensions with different volume fractios cmp of the
magnetic particles; (bottom) saturation birefringence as a function of
cmp.
17
Oscillatory dynamics of ferromagnetic nanorods
in gelatin solutions
K. Birster, A. Tschöpe, R. Birringer
Universität des Saarlandes, FR 7.2. Experimentalphysik, 66123 Saarbrücken
1
Introduction
The dynamics of nickel nanorods
suspended in gelatin solutions was
investigated using oscillating magnetic
fields combined with optical transmission
measurements. We focused on (i) the
effect of gelatin adsorption and/or fluid
viscosity on the viscous relaxation in the
sol state, and (ii) on the emerging elastic
interaction between the nanorods and
the polymer network formed during
physical gelation. The primary objective
was to derive the reference value for the
hydrodynamic size of the nanorods in a
gelatin matrix, which is a prerequisite for
quantitative analysis of the field-induced
rotation of ferromagnetic nanorods in
hydrogels.
1
2
and
. 3
We approximated the geometry factor Kv
of the nanorods by Tirados expression for
cylindrical particles of length L and
diameter D [3]. The magnitudes of L and
D are determined by the length l and
diameter d of the bare nanorods and the
effective thickness λ of an adsorbed
gelatin layer, i.e. L=l+2λ and D=d+2λ,
Fig. 1. In reference to a measurement of
the bare nanorods in water, the layer
thickness λ could be estimated from the
relaxation frequency of the same
nanorods in gelatin solution.
Methods
Ferromagnetic nickel nanorods were
synthesised by pulsed electrodeposition
of nickel into a nanoporous AAO
template [1,2]. After dissolution of the
oxide layer, the colloidal suspension was
sterically
stabilised
using
PVP
as
surfactant. In the following, PVP-coated
rods are denoted as bare Ni-rods in
contrast to rods with adsorbed gelatin
layer.
The rotational motion of ferromagnetic
nanorods
driven
by
an
external
oscillating magnetic field is monitored
through optical transmission measurements (OF-MOT). In the Voigt–Kelvin
model
the
characteristic
relaxation
frequency is a function of a geometry
factor Kv and magnetic moment m of the
nanorods on the one hand and the
viscosity η and shear modulus G of the
matrix on the other hand,
1
with
18
1 Fig. 1: Simplified geometrical model
of a nanorod with adsorbed gelatin
layer of effective thickness λ.
Gelatin solutions in the used concentration range c < 3 g/dl at a sol temperature of 40°C are Newtonian fluids,
hence, G vanishes and eq. (1) simplifies
to γ=1. During gelation, a macroscopic
polymer network is formed which leads
to an elastic interaction with the
nanorods, represented by a finite static
shear modulus G.
Results
Starting point of the measurements was
a pure aqueous colloidal dispersion of
nanorods. We increased the gelatin concentration in small steps and performed
OF-MOT
measurements
after
equilibration.
The
relaxation
frequency
decreased with every addition of gelatin,
Fig. 3: Effective layer thickness of
adsorbed gelatin as a function of
the gelatin concentration.
Fig. 2: Characteristic relaxation
frequency as a function of the
gelatin concentration.
Fig 2. Referring to Eq. 1, this decrease
could be caused by (i) the increasing
viscosity of the gelatin sol, and/or (ii) a
change of the hydrodynamic size of the
nanorods due to the adsorption of gelatin
molecules. In order to discriminate the
two effects, we studied the reversibility
with respect to a concentration change.
A dispersion of nanorods in 10-3 g/dl
gelatin sol (blue marker) was diluted by
a factor 1:14. The relaxation frequency
increased slightly (red marker) but did
not resume the initial value at that
concentration. Even the application of
ultrasound did not significantly change
the relaxation frequency (green marker).
These results suggested irreversible
adsorption of gelatin molecules as
primary
origin
of
the
decreasing
relaxation frequency. The increase in
layer thickness could be formally
described by a Langmuir adsorption
isotherm with a plateau of λ=22 nm
reached at 10-2 g/dl. The further increase
at higher concentrations was also found
to be irreversible as revealed from
measurements after dilution by 1:14 of a
10-1 g/dl sol, Fig. 3. This suggested a
second adsorption regime which probably
involves reorientation of the molecules in
the adsorbate layer. Hence, the final
relaxation frequency provided the hydrodynamic size of the nanorods including
an adsorbed gelatin layer necessary for
the analysis of further measurements in
hydrogels.
by macroscopic SAOS measurements,
Fig. 4. By contrast, the analysis of OFMOT measurements in terms of the
Voigt-Kelvin model revealed a significant
temporal shift of the increase in shear
modulus by >1000 min. This suggested
that the oscillatory dynamics of the
nanorods did not capture an elastic
interaction until the mesh size of the
hydrogel network decreased to ≈70 nm.
Fig. 4: Comparison of macroscopic and nanoscopic measurement of the gelation process of a
gelatin hydrogel.
References
[1]
[2]
[3]
Masuda and Fukuda; Science 268 (1995), p.
1466.
Bender P., Günther A., Tschöpe A. and
Birringer R.; J. Magn. Magn. Mater 323
(2011), p. 2055.
Tirado and de la Torre; J. Chem. Phys. 73
(1980), p. 1986.
After determination of the particle factor
K of the nanorods in a 2 wt% gelatin sol,
the sample temperature was quenched
from 40°C to 21.6°C. A gelation point at
120 min was independently determined
19
Field Induced Rotation of Ferromagnetic
Nanorods in an Elastic Matrix
C. Schopphoven1, A. Tschöpe1
1
Experimentalphysik, Universität des Saarlandes, Geb. D2.2, 66123 Saarbrücken
Introduction
Magnetic particles allow the contactless
application of forces or torques through
external magnetic fields which enables to
use such particles as microrheological
probes or as active component in soft
magnetic actuators. We investigate the
rotational motion of Ni nanorods in soft
viscoelastic matrices. The rotation angle
at an external magnetic field depends on
various factors. The present report focuses on the magnetic torque which is
determined by the intrinsic magnetic
properties of the nanorods and on the
interparticle interaction at increasing
volume fraction, i.e. decreasing interparticle spacing.
Methods
Ni nanorods with a mean diameter of
~20 nm and a mean length of ~250 nm
were synthesized by electro-deposition of
nickel into porous alumina (AAO) templates. The nanorods were released from
the templates by dissolving the alumina
layer in dilute NaOH, with the surfactant
polyvinyl-pyrrolidone added to prevent
agglomeration.
For the magnetic characterization of the
nanorods, the aqueous suspension was
mixed with a 10wt% gelatin sol at 60°C.
A magnetic field was applied to orient
the rods parallel in field direction and
was maintained during cooling down to
room temperature resulting in a magnetically textured rigid ferrogel. The field
and direction-dependent magnetization
was measured in a vector vibrating sample magnetometer (VVSM) which provided the magnetization components parallel and perpendicular to the applied field.
The interparticle interaction was investigated by static magneto-optical measurements of nanorods dispersed at varying volume fraction in mechanically soft
matrices of formaldehyde chemically
cross-linked gelatin (G~25Pa).
20
Due to their acicular shape, Ni nanorods
exhibit significant optical anisotropy, resulting in the orientation-dependent extinction of linearly polarized light. For
rods parallel to the polarization direction,
a minimum intensity Imin is transmitted,
while for the perpendicular case, a maximum intensity Imax is obtained. Calibration of these values enables to determine
the orientation angle ω at an applied
field from the transmitted intensity I,
cos
.
(1)
The orientation of the nanorods is measured as a function of a magnetic field
applied perpendicular to the initial orientation. The rotation angle is plotted
against the magnetic torque acting on
the rods, assuming coherent rotation of
the magnetic moment. A linear fit is then
applied, providing a slope s,
1
∙
,
(2)
where KV is a shape-dependent constant
of the nanorods and Geff the effective
shear modulus of the matrix. Provided KV
and Geff are constant, a change in slope s
upon variation of the volume fraction of
nanorods indicates the presence of interparticle interaction.
Results – VVSM
When considering the rotation of Ni nanorods, knowledge of the magnetic
torque acting on the particles is of vital
importance. In the simplest case this
torque can be expressed as the cross
product between the flux density vector
and the magnetic moment
or alternatively the product between the flux
density amplitude and the component of
the magnetic moment perpendicular to
the field mperp. In conventional magnetometry however, only the magnetization
component parallel to the field is ob-
tained and the perpendicular component
has to be estimated using a model for
the magnetization rotation.
ple models sufficiently reflects the magnetization behavior for larger fields. In
future experiments this effect will be
further investigated for different angles
between the main rod axis and the applied magnetic field.
Results - MOT
Fig. 1: Sketch indicating coherent (left) and incoherent segmented (right) magnetization rotation.
Fig. 1 shows a sketch of two possible
magnetization rotation processes, coherent rotation and incoherent rotation
starting at the rod ends, here simplified
by three segments.
Fig. 3: Slope s as a function of the interparticle
spacing estimated from the particle volume
fraction. The dashed line serves as a guide to the
eye.
Fig. 2: Magnetic torque acting on Ni nanorods
calculated
from
conventional
magnetization
measurements
assuming
coherent
(red)
or
segmented (blue) magnetization change and from
measured mperp (black).
The blue and red lines in Fig. 2 show the
torques calculated from the measured
parallel component mpar(H) using the
respective rotation models. The large
discrepancy illustrates the uncertainty
that arises from not actually measuring
mperp in conventional VSMs.
The black line represents the torque directly calculated from the measured
magnetization component perpendicular
to the applied field. For low field
strengths the torques are fairly consistent. As the field strength increases
however, significant
deviations
are
found, indicating that neither of the sim-
Fig. 3 shows the slope s obtained from
magneto-optical transmission measurements as a function of the mean centerto-center distance calculated from the
particle volume fraction, assuming ideally
homogeneously distributed particles in a
cubic arrangement. For higher particle
concentrations and thus lower spacing, a
reduction in slope can be observed, indicating that the rods are hampered in
their rotational movement. As magnetic
interparticle interaction is negligible on
the µm-scale, this effect can be attributed to elastic particle-particle interaction.
At large distances the slope approaches
a plateau value, reflecting the regime of
single particle behavior.
Acknowledgments
We thank Cindy L. Dennis and Robert
Shull from the National Institute of
Standards and Technology for performing the Vector VSM measurements and
SPP 1681 for funding.
21
Deformation mechanisms of magnetic gels
studied by computer simulations
R. Weeber, Ch. Holm
Institut für Computerphysik, Universität Stuttgart, Allmandring 3, 70569 Stuttgart
Our project is concerned with a
theoretical investigation of magnetic
gels. These hybrid materials, consisting
of magnetic particles immersed in a
hydrogel or elastomer, are of interest
due to the tunable interplay between
elastic and magnetic forces in them.
For example, magnetic gels can change
their elasticity and shape, when an
external magnetic field is applied. This
property makes them interesting for
applications in medicine and engineering.
Magnetic gels, also called ferrogels, can
today be synthesized in various ways. A
variety of both, different magnetic
nanoparticles and polymer matrices have
been used in order to alter the material's
properties.
So far, simulation models have mainly
been used to study the mechanisms of
deformation of ferrogels in external
fields, qualitatively.
Three
mechanisms
for
a
gel's
deformation in an external field can be
identified.
First, a gel deforms in a field gradient, as
magnetic particles tend to accumulate in
regions with a higher field.
Second, in magnetic gel's in which the
particles act as cross-linkers of the
network, a deformation occurs, due to a
strain exerted on the polymers, as the
magnetic particles they are connect to,
are aligned to a magnetic field.
The third mechanism is based on a
change of the interaction between the
magnetic particles caused by an external
field.
In the absence of a field, the magnetic
moments of the particles are randomly
aligned. Thus, there is no net interaction
between them.
When the magnetic moments get aligned
by an external field, however, this is no
22
longer the case. Magnetic particles
attract in the direction parallel to the
field and repel in the perpendicular
direction.
This mechanism can partly be captured
on the macroscopic scale by considering
a homogeneously magnetized linear
elastic material [1].
By
minimizing
the
sum
of
the
demagnetization energy and the elastic
energy, it can be shown that a spherical
sample deforms to an elongated shape in
a field.
It has, however, also been shown [2]
that the local structure of the magnetic
particles is important, and that different
configurations can lead to a different
deformation behaviour.
For this reason, we focus on particlebased simulation techniques, which
explicitly
track
the
position
and
orientation of the magnetic particles.
In order to better understand the
interplay between magnetic particles and
polymers, we have so far included the
polymers as bead-spring models into our
simulations, both, for particle-crosslinked
gels and for gels deforming due to the
change in magnetic interactions [3].
This, however, limits the size of the
model to a few hundred magnetic
particles.
In order to overcome this limitation and
approach experimentally more realistic
parameters, we have, however, recently
developed a model in which the polymers
are no longer explicitly included, but
rather represented as effective potentials
between the nanoparticles.
This allows us to include between 10 000
and 100 000 magnetic particles in the
system.
For nanoparticles with a size of 12 nm
and a volume fraction of 5%, this implies
a sample size of 700 nm up to two
micrometers.
As
mentioned
above,
the
local
configuration
of
the
magnetic
nanoparticles before cross-linking is
important. To account for this fact, we
therefore use configurations obtained
from simulations of a ferrofluid of similar
particles at a corresponding density.
This procedure also allows us to study
the case, where the gel is cross-linked in
an external field.
In our presentation, we will explain the
model
in
detail
and
show
first
measurements on the field- and elasticity
dependent deformation of the system.
Acknowledgments
The authors are grateful for financial
support from the DFG through the SPP
1686 and the Stuttgart Research Centre
for Simulation Technology (SimTech).
References
[1] Yu.L. Raikher and O.V. Stolbov.
Magnetodeformational effect in ferrogel
samples. JMMM, 258:2597, 2003.
[2] O. Stolbov, Yu.L. Raikher, and M.
Balasoiu. Modelling of magnetodipolar
striction in soft magnetic elastomers.
Soft Matter, 7:8484, 2011.
[3] R. Weeber, S. Kantorovich, and C.
Holm. Deformation mechanisms in 2d
magnetic gels studied by computer
simulations. Soft Matter, 8:9923, 2012.
23
Molecular simulations of liquid crystalline ferrofluids
S. D.Peroukidis and S.H.L. Klapp
Institute of Theoretical physics, Technical University of Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
Suspensions of magnetic nanoparticles
(MNP) in liquid crystalline (LC) matrices,
i.e LC-MNP hybdrid systems [1], is a
non-trivial avenue for obtaining materials
with programmable and controllable
functions. The LC-MNP hybrid, depending
on its morphology, is expected to possess remarkable properties such as directional sensitivity in space to external
magnetic and electric stimuli. The simplest of LC-MNP hybrids, ferronematics,
was coined by Brochard and de Gennes
in their theoretical investigation [2] four
decades ago. Surprisingly, realization of
uniaxial LC-MNP hydrid that consist of
local ferromagnetic domains has been
obtained recently, in suspensions of
platelike magnets immersed in thermotropic LC [3]. There is also strong current
interest in lyotropic suspensions of rodlike LC and MNP [4].
Here, motivated by these experimental
research, we attempt to clarify the role
of basic molecular features of mesogenic
and magnetic particles on the selforganization of such systems. To this end
we have performed canonical monte carlo computer simulations of binary mixtures of mesogenic Gay-Berne rod and
soft dipolar sphere particles. The soft
dipolar spheres have diameter  s*   s 
and the GB rods aspect ratio l *  l   
.The long range dipolar interactions are
treated using the Ewald method [5]. We
have implemented a modified Gay-Berne
potential to describe the rod-sphere interaction [6]. We have examined systems for a variety of particles compositions ( xr  N r N  0.8 , with N  N r  N s
where N r , N s is the number of rods and
spheres respectively) and total number
densities  *  N V , where V is the volume. The dipole moment is set
*  
  
0
3
s
1
2
 3 . It should be noted that
previous theoretical results in binary
mixtures of rod and sphere particles [7]
have shown that the LC phases can be
24
thermodynamically stable and support
considerable amounts of spheres depending on their relative size.
2.4
(a)
T*
Nem
2.0
(b)
I
Nb
I
T *1.6
1.2
SmB
Lamb
0.8
0.4
0.30

*
Figure 1. Tentative state diagrams of a mixture of
*
rods and dipolar spheres: (a) with  s  1 and
xr  0.8
and (b) with
0.31
 s*  2
and
0.32
* 0.33
0.34
xr  0.1 .

A temperature-density T * ,  *

state dia-
gram has been calculated for binary mixtures of N  720 particles, with spheres of
 s*  1 , for concentration xr  0.8 . Isotropic (I), nematic (Nem) and Smectic
(SmB) phases are found. The topology of
the diagram is shown in Fig 1a. Larger
systems of N  2000 and 4000 particles
have also been investigated to account
for finite size effects.
Figure 2: Representative snapshots of a mixture of
rods
and
xr  0.8
spheres
with
 s*  1 ,
*  3
and
in (a) I, (b) Nem and (c) SmB phase.
In the I phase the spheres form an isotropic network of wormlike chains, that is
also found in bulk dilute strongly interacting dipolar systems (see Fig. 2a). Interestingly, the I-N phase transformation
occurs at significantly higher temperatures in comparison to the system without dipolar interactions. Hence, the Nem
phase is enhanced in favor of the I
phase. A representative snapshot is
shown in Fig 2b.
A particular interesting finding is that the
Nem phase possess two distinct directors
i.e of rodlike mesogens and magnetic
spheres. Remarkably, the wormlike
chains are spontaneously unwrapped
within the Nem phase forming long range
orientationally ordered chains that are on
average parallel to the director of the
rods. Hence the Nem phase is uniaxial.
Even though the chains are ferromagnetic (polar) the phase does not show spontaneous magnetization since the polar
chains are arranged into an antiparallel
manner.
In the SmB phase the chains remain
continuous penetrating the soft layers of
rods and are oriented, on average, parallel to the layer normal as it is shown in
Fig 2c. These findings demonstrate that
not only ferronematics but also anisotropic ferrofluids with translational ordering can be formed in colloidal suspensions of rods and dipolar spheres. We
term these fluids uniaxial ferrosmectics.
tion of these mixtures: biaxial liquid
crystalline ferrofluids (nematic and Lamellar) are found. The temperaturedensity T * ,  * state diagram has been


calculated for binary mixtures of N  1251
particles for xr  0.1 (see Fig 2b).
At lower temperature the system undergoes an I-Nb phase transformation. The
most striking finding is that the two nematic directors are on average perpendicular to each other. This means that on
average the dipolar spheres orient perpendicular to the mesogenic rods and
therefore a biaxial ferrofluid is formed.
Simulations of larger systems of N  2536
particles and N  4000 where performed
for selective states to check for finite size
effects. It is found that the nematic ordering is close to that of the smaller systems and the nematic directors are spontaneously perpendicular to each other.
At lower temperature a lamellar phase is
exhibited that consists of alternating layers of rods ans spheres (see Fig. 3b). We
term this novel ferrolamellar phase LC
Lamb.
These intriguing results provide a comprehensive guide for understanding real
systems and may stimulate further experimental investigations in lyotropic LCMNP hybrid systems.
Acknowledgments
This research has been financed by DFGPriority Programme 1681 ‘Field controlled
particle matrix interactions: synthesis
multiscale modeling and application of
magnetic hybrid materials’.
References
Figure 3. Representative snapshots of a mixture of
rods and spheres with with
 2
*
s
and
xr  0.9
in
(a) Nb and (b) Lamb phase.
In binary mixtures of rods and dipolar
spheres (with  s*  1.5,1.7 ) uniaxial ferronematics and defect rich smectic phases
are obtained. The insertion of even larger magnetic spheres, with  s*  2 , dramatically affects the molecular organiza-
[1]
[2]
[3]
[4]
[5]
[6]
[7]
S. Saliba et al., Nanoscale, 5, 6641 (2013).
P. de Gennes and F. Brochard, J. Phys., 31,
691 (1973).
A. Mertelj et al., Nature, 504, 237 (2013).
S. Kredentser et al., Soft Matter, 00,0000
(2013); K. May et al., Langmuir, 00, 0000
(2014).
J. Jordanovic and S. H. L. Klapp, Phys. Rev. E,
79, 021405 (2009).
D. J. Cleaver, C. M. Care, M. P. Allen, and M.
P. Neal, Phys. Rev. E, 54, 559 (1998)
S. D. Peroukidis, A.G.Vanakaras and D.J.
Photinos, J. Mater. Chem. 20, 10495 (2010).
25
Mesoscopic modeling of ferrogels: from tunable
relaxation dynamics to nonlinear stress-strain behavior
P. Cremer1, G. Pessot1, M. Tarama1,2, B. ten Hagen1, K.
Popowa1, A. Kaiser1, E. Allahyarov1, H. Löwen1, A. M.
Menzel1
Institut für Theoretische Physik II: Weiche Materie, Heinrich-Heine-Universität Düsseldorf, D-40225
Düsseldorf, Germany
1
2
Department of Physics, Kyoto University, Kyoto 606-8502, Japan
Introduction
As is commonly known, ferrogels and
magnetic elastomers show fascinating
material properties like elastic moduli
that are reversibly tunable by external
magnetic fields [1]. These features arise
from the coupling between the elastic
and magnetic components of the
composite systems. It is our goal to
understand the underlying processes on
a mesoscopic level based on simple
phenomenological model considerations
of the composite systems and by
developing
a
statistical
mechanical
theory.
Tunable relaxation dynamics
In this first study we address the
question how the dynamic response of
magnetic gels can be adjusted to a
requested demand [2]. We demonstrate
the impact of at least three factors on
the
dynamic
material
properties:
orientational memory of the magnetic
particles, their spatial distribution in the
polymer matrix, and an externally
applied magnetic field. These calculations
are performed using a simple dipolespring model that we recently introduced
[3]: dipolar magnetic particles are
connected by harmonic springs that
mimic the elastic interactions mediated
by an embedding polymer matrix in the
real materials. In contrast to previous
studies in the field, we use as one input
to our investigation an actually observed
magnetic particle distribution. The data
were extracted from tomography results
on a real experimental sample in the
Odenbach group [4]. This interaction
with experimental projects became
possible within the SPP 1681 and shall be
extended in the future.
26
Structural control of elastic moduli
and non-affine deformations
Here we use the same dipole-spring
model [2] to systematically study the
following question. In theoretical model
calculations often very regular lattice
arrangements of the magnetic particles
are
assumed.
Furthermore,
affine
deformations
are
applied,
i.e.
all
distances throughout the sample are
modified by the same ratio. We
demonstrate that this assumption of
affine deformations becomes increasingly
erroneous the more randomized the
particle distribution becomes [5]. For a
particle distribution extracted from a real
experimental sample (see previous
paragraph) even a qualitatively incorrect
behavior is obtained as a function of the
magnetization. Apart from that, we
determine and compare the behavior of
the dilative and compressive elastic
modulus as a function of the magnetic
moment for various different spatial
particle arrangements [5].
Nonlinear stress-strain behavior
To analyze the stress-strain behavior, we
implemented a more refined mesoscopic
approach than the simplified dipolespring model. The space between the
magnetic particles is now divided into
discrete cells. To represent the elastic
response of the polymer matrix, affine
deformations are assumed for each cell
that follow the rules of elastic continuum
theory. In this way, we investigate for
example the stress-strain behavior under
a uniaxial extension of the sample [6].
Stretching an anisotropic sample of
permanently
magnetized
particles
parallel to its initial magnetization
direction,
we
observe
a
marked
nonlinearity in the stress-strain curve.
We show that this nonlinearity is
connected to the interplay between the
magnetic and elastic components. Due to
the strain-induced distance changes in
the sample, the magnetization direction
reorients into a direction perpendicular to
its initial orientation. The magnetization
of the sample becomes inhomogeneous
during this reorientation process. Later in
the SPP, we intend to compare these
results to those obtained from the
macroscopic theories [7].
Induced deformations in bilayered
magnetic elastomers
Using a continuum theory, we analyze
the strains that are induced by an
external magnetic field in prism-shaped
bilayered magnetic elastomers [8]. The
two layers have different magnetic
susceptibilities, with the layer interface
oriented perpendicular to the external
field direction. Interestingly, we find that
the overall deformational response can
be larger for the bilayered composite
than for the single-layered materials of
identical volume, and can even be of
opposite kind. As a next step we plan to
embed such bilayered prisms into a nonmagnetic polymeric matrix and study the
overall deformations.
Scale bridging to microscopic world
Together with the Holm project we are
working on linking microscopic simulation
approaches to the mesoscopic models.
Resolving by a bead-spring model a
polymer chain that connects two
magnetic
particles,
Monte-Carlo
simulations provide the probabilities to
find a certain configuration of the
system.
From
these
results,
we
determine the parameters and functional
forms of the mesoscopic models from the
input of the microscopic simulations [9].
Further activities
Several further studies have been started
in
the
field.
Together
with
the
Auernhammer project, we analyze the
magnetic-field induced deformations of
chains of magnetic particles that are
embedded in a gel matrix [10]. In
collaboration with the Wagner project,
we investigate the diffusion properties of
magnetic spindle-like particles in a solute
[11]. Finally, we study the collective
behavior of self-propelled magnetic
particles as a model system for
swimming magnetic bacteria [12]. Due
to
the
low
Reynolds
numbers
characterizing bacterial swimming, the
aqueous surrounding of the bacteria
appears as a highly viscous matrix
environment.
Perspective
In the future, the mesoscopic model
approaches shall be pursued to further
connect them to real experimental
systems. Our central next step will be to
establish a statistical theory for the
behavior of the magnetic particles. This
description will be applied to extend the
characterization of the materials and
allow a scale bridging to established
macroscopic theories in the SPP.
Acknowledgments
We thank G. Auernhammer, D. Borin, C.
Holm, S. Huang, S. Odenbach, C.
Passow, J. Wagner, and R. Weeber for
present collaborations as well as the DFG
for support of our work within the SPP
1681.
References
[1]
G. Filipcsei, I. Csetneki, A. Szilagyi, and M.
Zrinyi, Adv. Polym. Sci. 206, 137 (2007).
[2] M. Tarama, P. Cremer, D. Y. Borin, S.
Odenbach, H. Löwen, and A. M. Menzel,
arXiv:1406.6979 (2014).
[3] M. A. Annunziata, A. M. Menzel, and H.
Löwen, J. Chem. Phys. 138, 204906 (2013).
[4] D. Günther, D. Y. Borin, S. Günther, and S.
Odenbach, Smart Mater. Struct. 21, 015005
(2012).
[5] G. Pessot, P. Cremer, D. Y. Borin, S.
Odenbach, H. Löwen, and A. M. Menzel,
arXiv:1407.0309 (2014).
[6] P. Cremer, H. Löwen, and A. M. Menzel, in
preparation.
[7] S. Bohlius, H. R. Brand, and H. Pleiner, Phys.
Rev. E 70, 061411 (2004).
[8] E. Allahyarov, A. M. Menzel, L. Zhu, and H.
Löwen, Smart Mater. Struct. (accepted);
arXiv:1406.6412 (2014).
[9] G. Pessot, R. Weeber, C. Holm, H. Löwen, and
A. M. Menzel, in preparation.
[10] S. Huang, P. Cremer, A. M. Menzel, and G.
Auernhammer, in preparation.
[11] C. Passow, B. ten Hagen, H. Löwen, and J.
Wagner, in preparation.
[12] K. Popowa, A. Kaiser, and H. Löwen, in
preparation.
27
Macroscopic behavior of ferronematic gels and
elastomers
H.R. Brand1, H. Pleiner2
1
2
Theoretische Physik III, Universitaet Bayreuth, 95440 Bayreuth
Max Planck Institute for Polymer Research, 55021 Mainz
Introduction
We use the framework of generalized
hydrodynamics to derive a set of partial
differential equations that describe the
macroscopic dynamic behavior of ferronematic gels and elastomers. These systems combine liquid crystalline, ferrofluidic and elastic aspects. Their hydrodynamic description comprises that of ferronematics [1,2] ferrogels [3,4], and of
nematic elastomers [5-7], in addition to
crosscoupling effects specific for ferronematic gels and elastomers.
Results
In this first communication [8] we will
concentrate on the case that there is no
permanent magnetization present, nor
any strong external magnetic field. Thus,
the nematic director is the only preferred
direction in the system, rendering the
latter uniaxial.
The dynamic variables necessary to describe macroscopically ferronematic gels
and elastomers are the standard fluid
ones (mass density, momentum density
and energy density), the nematic ones
(director reorientation, scalar nematic
order parameter), the magnetic ones
(density of magnetic particles, magnetization, and associate Maxwell fields), the
elastic ones (the strain tensor field, a
possible solvent concentration, and relative rotations of the director relative to
the network). The latter are generally
penalized energetically and show a slow
dynamics. They are a hallmark of elastomers with a preferred direction and have
been introduced by P.G. de Gennes [9].
There are three reversible dynamic
crosscouplings of special interest. First,
the nematic and the magnetic degree of
freedom are coupled such that a deformed director field gives rise to a magnetization current (a temporal change of
28
the magnetization), and vice versa, a
magnetization (or small external field)
triggers a director rotation. Second,
magnetization is coupled to relative rotations (between the director and the network!), where the former induces temporal changes of the latter, or vice versa,
a relative rotation (maybe created by an
electric field) leads to a magnetization
current. This is a very specific effect for
ferronematic gels and elastomers. Finally, also (shear) flow can induce relative
rotations (and vice versa) with the result
that shear flow leads to temporal changes of the magnetization, the director orientation, and the relative rotations.
These reversible effects show up in the
in-phase response to oscillatory shear,
while the additional dissipative effects
are out-of phase.
Acknowledgment
We thank the Deutsche Forschungsgemeinschaft for partial support through
the Priority Program 1681.
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
E. Jarkova, H. Pleiner, H.-W. Mueller, A. Fink,
and H.R. Brand, Eur. J. Phys. E 5, 583 (2001)
E. Jarkova, H. Pleiner, H.-W. Mueller, and H.R.
Brand, J. Chem. Phys. 118, 2422 (2003))
E. Jarkova, H. Pleiner, H.-W. Mueller, and H.R.
Brand, Phys. Rev. E 68, 041706 (2003)
S. Bohlius, H. Pleiner, and H.R. Brand, Phys.
Rev. E 70, 061411 (2004)
H.R. Brand and H. Pleiner, Physica A 208, 359
(1994)
H.R. Brand, H. Pleiner, and P. Martinoty, Soft
Matter 2, 182 (2006)
A. Menzel, H. Pleiner, and H.R. Brand, J.
Chem. Phys. 126, 234901 (2007); J. Appl.
Phys. 105, 013503 (2009); Eur. Phys. J. E 30,
371 (2009)
H.R. Brand and H. Pleiner, to be submitted
P.G. de Gennes, in Liquid Crystals of One- and
Two-Dimensional Order, edited by W. Helfrich
and G. Heppke (Springer, Berlin, 1980), pp.
231 ff.
Development of a magneto-mechanical continuum
model for ferrogels
A. Attaran1, J. Brummund1, T. Wallmersperger1
1
Institut für Festkörpermechanik, Technische Universität Dresden
Ferrogels consist of a soft polymer matrix
- usually made up of chemically crosslinked polymer networks - and a pore “ferrofluid” [1, 2]. The pore fluid usually carries magnetic particles of a typical size of
10 nm [3], see Fig. 1. Ferrogels are characterized by their low stiffness, large deformation, and water absorption [3].
Figure 1: Microstructure of a ferrogel
In this work a systematic development of
a coupled magneto-mechanical model for
ferrogels is presented. Considered as a
multicomponent, multiphase medium, the
field equations of ferrogels are derived
within the framework of continuum mechanics of mixtures. The procedure of deriving the equations begins by the introduction of the kinematic relations, the
balance laws and the Maxwell's relations
of electromagnetism. The balance laws include the balance of mass, momentum,
angular momentum, energy and entropy.
In the process of modeling, the suitable
free energy function is introduced and
thermodynamically consistent constitutive laws are derived. The field equations
for the ferrogels are then obtained by
plugging the constitutive relations back
into the balance laws. The derived set of
field equations complemented by appropriate initial, boundary and transition conditions define a well-posed coupled magneto-mechanical problem for describing
the behavior of ferrogels.
Owing to its versatility, the finite element
method (FEM) is exploited to solve the
aforementioned problem. This enables us
to study (i) the influence of the magnetic
field on the magnetic particles in the polymer gel, (ii) the interaction of the particles with the polymer network, and (iii)
the resulting mechanical deformation of
the gel. Thus, depending on the applied
magnetic field, the resulting deformation
of the gel, and the attainable restoring
forces for example of a ferrogel actuator
can be determined.
Acknowledgments
This research has been financially supported by the Deutsche Forschungsgemeinschaft (DFG) in the framework of the
Priority Programme (SPP 1681).
References
[1] E. Jarkova, H. Pleiner, H.-W. Müller, and H.R.
Brand. Hydrodynamics of isotropic ferrogels. Phys.
Rev. E, 68:041706, 2003.
[2] S. Bohlius, H.R. Brand, and H. Pleiner. Macroscopic dynamics of uniaxial magnetic gels. Phys.
Rev. E, 70:061411, 2004.
[3] M. Zrínyi, L. Barsi, and A. Büki. Ferrogel: a new
magneto-controlled elastic medium. Polymer Gels
and Networks, 5(5):415 – 427, 1997.
29
XFEM model generation and magneto-mechanical
simulation of MRE
Institute of Solid Mechanics, Technische Universität Dresden, 01062 Dresden, Germany
Introduction
Numerical simulation techniques provide
a powerful tool to determine and understand the behavior of composite material
systems. In particular the extended finite
element method (XFEM) is applied to
generate numerical models of magnetorheological elastomers (MRE) taking
into account their heterogeneous material structure. XFEM offers the possibility
to use nonconforming computational
meshes which do not have to be adapted
to material interfaces. Hence, the meshes are independent of the location of
discontinuities. A comprehensive review
on XFEM can be found in, e.g., [1].
Selected results obtained by the convergence analysis are depicted in Fig. 2 for
two-dimensional linear and quadratic
elements. The computed fields converge
to their exact solution if the mesh is refined with the rate of convergence and
the error level being influenced by the
polynomial degree of the approximation.
Verification by convergence analysis
During the implementation process it is
mandatory to verify the program code.
That is, to compute error levels and investigate the convergence behavior of
the numerical approach. As analytical
solutions which are required as a reference, are rarely available for coupled
magneto-mechanical problems, an analytic solution has been derived at the
beginning of this project and published in
[2]. Both domains of the heterogeneous
structure presented in Fig. 1 are characterized by isotropic, linear magnetic and
elastic material. The assumption of small
deformations is considered here.
Figure 2: Convergence behavior of bilinear (solid
lines) and biquadratic elements (dashed lines) of
magnetic (crosses), mechanic (squares) and coupled magneto-mechanical field problems (circles)
[2].
Analysis of particle interactions
After the analysis of its numerical properties, XFEM modelling of magnetomechanical problems [3] has been used
to analyze the influence of external fields
on magnetic particles of different shapes
[4] also considering large deformations.
One application in [4] examines the reorientation of an elliptic inclusion subjected
to a homogeneous magnetic field not
aligned to the principal axes of the ellipse. The torque acting on the magnetically soft elliptic inclusion can be calculated. These results are currently discussed with work groups in Saarbrücken
and Dresden (IFW).
Generating microstructure models
Figure 1: Circular inclusion with homogeneous
magnetic and mechanical loadings [2].
30
In order to generate more realistic isotropic and anisotropic, polydisperse particle distributions, the XFEM modeling
approach has been enhanced by a random addition algorithm and algorithms
to represent curved interfaces in two and
three dimensions as illustrated in Fig. 3.
(a)
(b)
Figure 3: (a) Two-dimensional and (b) threedimensional random microstructures.
The effective response of these random
microstructures is currently evaluated by
applying computational homogenization
techniques [5] using the assumption of
small deformations. Exemplary results
for simpler microstructures are shown in
Fig. 4.
(ii) Alternatively a direct image-based
model generation, i.e., the conversion of
CT images into XFEM models of the local
material structure is considered. Depending on the resolution of available images,
one can distinguish between images resolving individual particles (microscale)
or clusters of particles on a larger length
scale (mesoscale). Fig. 6 (a) exemplarily
shows the CT image of some particle
clusters [6].
A marching cube algorithm has been
combined with the level-set approach to
locate the material interface between
magnetic particles and the surrounding
matrix in a regular XFEM mesh. Adaptive
mesh refinement based on a quadtree
algorithm is used to improve the resolution of interfaces (Fig. 6 (b)), and the
approximation of field quantities (Fig.
6(c)).
(a)
(b)
Figure 4: Effective magnetization curves and actuation stresses of a chain-like microstructure [5].
Ongoing work involves the incorporation
of data available from the characterization of the microstructure. Two approaches are followed:
(i) Experimentally determined particle
size distributions of real MRE specimen
are used in conjunction with the random
addition algorithm to generate statistically similar numerical models. Figure 5
originates from the postprocessing of a
computed
tomography
(CT)
image
(thanks to T. Gundermann and S. Odenbach, Institute of Fluid Mechanis, TU
Dresden).
(c)
Figure 6: (a) Mesostructural CT image [6], (b)
adaptively refined XFEM mesh and (c) contour plot
of the computed magnetic field.
Acknowledgments
The present study is funded by the German Research Foundation (DFG), Priority
Program (SPP) 1681, grant KA 3309/2-1.
References
[1]
[2]
[3]
Figure 5: Particle size distribution obtained by
postprocessing of a CT image.
[4]
[5]
[6]
T.P. Fries and T. Belytschko, Int. J. Numer.
Meth. Engng. 84, 2010.
C. Spieler et al. Analytic and numeric solution
of a magneto-mechanical inclusion problem,
Arch. Appl. Mech., accepted manuscript.
M. Kästner et al. Int. J. Numer. Meth. Engng.
93, 2013.
C. Spieler et al., Tech. Mech. 34, 2014.
C. Spieler et al. Acta Mech. 224, 2013.
D. Günther et al. Smart Mater. Struct. 21,
2012.
31
Comparative study of nanoparticle motion by
Mössbauer spectroscopy and AC-susceptometry
J. Landers1, L. Roeder2, A. M. Schmidt2, H. Wende1
1
2
Faculty of Physics and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen
Department Chemie, Institut für Physikalische Chemie, Universität zu Köln
Introduction
Results
Although composite materials made of
magnetic nanoparticles and hydrogels
have been of great interest in the last
years, it has not been fully understood,
to which degree the free motion of the
nanoparticles is constrained. Many of the
most often used techniques are sensitive
to the macroscopic magnetic moments,
while the movements of individual particles cannot be determined. Therefore, a
combined approach of AC-susceptometry
and Mössbauer spectroscopy, measuring
the diffusive motion of iron ions on the
atomic level is a promising method to
provide new information.
Mössbauer spectra of the acicular nanoparticles in 60wt% sugar solution (Fig. 2)
display a continuous increase of line
width upon increasing temperature
matching the decrease in viscosity given
by literature values as expected for a
system which allows free particle motion.
AC-susceptibility data from the same
sample measured by a SQUID AC-option
exhibit a similar dependence of the maximum in the imaginary part ’’ on the
frequency, consistent with results from
Mössbauer spectroscopy (Fig. 3).
While we observed a continuous increase
in line width for the sugar solution upon
rising temperature, the nanoparticles in
hydrogels display rapid line broadening
in the hydrogel melting region and a
slight further increase for higher temperatures. Line widths in the liquid hydrogel
state are about 10-25mm/s for different
degrees of cross-linking. This is within
the same magnitude as for the nanoparticles in sugar solution, indicating similar
mobility of the nanoparticles.
In contrast to this result the ACsusceptibility even of the softest (least
MBA content) hydrogel sample is marginal compared to that of the sugar solution, starting to increase only at the lowest accessible frequencies.
Methods
Acicular hematite nanoparticles (length
390nm, diameter 85nm) were added to
60wt% sugar solution as well as to 3
polyacrylamide (PAAm) hydrogels with
different amounts of methylene bisacrylamide (MBA) as crosslinker [1].
AC-susceptibility of all four samples was
measured by a Quantum Design SQUID
magnetometer (MPMS-5S) in an airtight
sample holder at temperatures of 270 –
320K. Mössbauer spectra in the same
temperature region were recorded using
a self-constructed sample holder with an
integrated Peltier element for temperature control and a high-velocity Mössbauer setup.
Figure 1: The photon energy is varied by moving
the 57Co-source utilizing the Doppler effect. By the
same effect, nanoparticle motion in the gel/fluidlike sample causes distinct line broadening in the
Mössbauer spectrum [2].
32
Figure 2: Mössbauer spectra of acicular nanoparticles in 60wt% sugar solution. Continuous line
broadening verifies enhanced nanoparticle motion.
[2]
P. Fornal and J. Stanek, Acta Phys. Pol. A,
114, 1667-1673 (2008)
Figure 3: Normalized AC-susceptibilities of acicular
nanoparticles in 60wt% sugar solution (filled
squares: real component ’, open squares: imaginary component ’’).
A possible explanation for this apparent
contradiction could be different reactions
of both methods to the constrained nanoparticle motion in the hydrogels. ACsusceptibility is primarily sensitive to
particle rotation, while Mössbauer spectroscopy provides information on the
motion of iron constituents on the atomic
level and is therefore expected to include
effects of rotational as well as translational motion.
Outlook
In the near future combined AC- and
Mössbauer measurements on anisotropic
particles with different aspect ratios
should verify whether rotational and
translational motion can be clearly resolved by Mössbauer spectroscopy.
As another approach, planned measurements of superparamagnetic nanoparticles in highly viscous ferrofluids could
allow us to distinguish between, and collect information on Néel and Brownian
relaxation processes at the same time.
Acknowledgments
We acknowledge funding by the DFG
through SPP1681 (WE2623/7-1) and essential technical support from U. von
Hörsten.
References
[1]
L. Roeder, P. Bender, A. Tschöpe, R. Birringer,
and A. M. Schmidt, J. Polym. Sci. Part B:
Polym. Phys., 50(24), 1772-1781 (2012)
33
Dynamic magnetic investigations of the particlematrix interaction of magnetic hybrid materials
H. Remmer1, C. Kuhlmann1, J. Dieckhoff1, A. Lak1, E. Roeben2,
A. M. Schmidt2, F. Ludwig1
Institut für Elektrische Messtechnik und Grundlagen der Elektrotechnik, TU Braunschweig, Hans- Sommer-Str.
66, 38106 Braunschweig
2
Institut für Physikalische Chemie, Universität zu Köln, Luxemburger Str. 116, 50939 Köln
1
Dynamic magnetic measurements on
MNP suspensions with different viscosities
The determination of the local viscosity
of the carrier medium of magnetic nanoparticle (MNP) suspensions utilizing dynamic magnetic measurement techniques such as magnetorelaxometry
(MRX) and ac susceptibility (ACS) is
based on the dependence of the Brownian time constant on viscosity.
We have prepared suspensions of singlecore and multicore Fe3O4 and single-core
CoFe2O4 nanoparticles. As model systems, we especially focus on single-core
particle systems with blocked magnetic
moments, i.e., the dynamics of the vast
majority of particles are dominated by
the Brownian mechanism. As media, DI
water, water-glycerol mixtures, PEG and
TEG were used.
Fig. 1: Normalized MRX curves measured
on single-core MNPs SHP-25 from Ocean
Nanotech in different water-glycerol mixtures.
Fig. 1 depicts MRX curves measured with
our fluxgate setup on single-core Fe3O4
MNPs in DI water-glycerol solutions.
Since the viscosity increases with rising
glycerol volume fraction, the decay of
the magnetic signal slows down. To es-
34
timate suspension viscosity, the measured curves were fitted with the cluster
moment superposition model (CMSM)
[1,2].
ACS measurements and measurements
of the phase lag between the samples’
magnetic moment and a rotating magnetic field were performed on identical
samples. As for the MRX measurements,
a monotonous shift of the position of the
imaginary part of the ACS and of the
phase lag towards lower frequencies was
observed. As a rough approximation, the
viscosity was estimated by assuming
that the maximum of the imaginary part
is at ·B = 1.
Fig. 2 depicts the obtained viscosities as
a function of glycerol volume fraction in
comparison with the values calculated
using Cheng’s formula [3] and measured
with a plate-plate rheometer.
Fig. 2: Viscosity as a function of glycerol
volume fraction.
As a novel magnetic technique, magnetic
particle spectroscopy (MPS) was applied.
Whereas the basic coil setup is similar to
ACS, sinusoidal excitations fields with
amplitudes up to 25 mT are applied,
driving the nanoparticles into saturation.
As a consequence, the detection signal
contains higher harmonics. In Fig. 3 the
spectral magnitudes of the odd harmonics measured on the same samples as
above are shown. Obviously, the spectra
vary with increasing viscosity in a
strongly nonlinear manner. To analyze
the complex response, real and imaginary parts of the individual odd harmonics are compared to theoretical results
based on a refined Debye-based magnetization model [4].
Fig. 3: Spectral magnitudes of odd harmonics for different water-glycerol mixtures.
Nanorheology utilizing ACS of more complex MNP suspensions, such as polymer
solutions, was presented in [5]. So far,
the analysis was carried out applying the
Debye model including a distribution of
hydrodynamic particle sizes. However,
the gradual decrease of the maximum
value of the imaginary part with increasing viscosity and the appearance of
shoulders in the spectra cannot be explained with such a simple model. Since
it cannot be assumed that the (local)
viscosity of a complex polymer solution
is described by a single value, we extended the Debye model by incorporating
a bimodal distribution of viscosity, thereby obtaining much better fits of the experimental spectra.
Setups for temperature dependent
measurements of the ac susceptibility
Temperature dependent measurements
of the ACS are desirable since the
Brownian time constant depends on
temperature via the – generally nonlinear – temperature dependence of the viscosity and the thermal energy. In addition, temperature plays an important role
in the sol-gel transition of thermogels.
We have extended two of our standard
measurement techniques for variations
of sample temperature: a fluxgate based
system allowing measurements between
a few Hz up to about 10 kHz and a new
high-frequency (HF) ACS system which
allows measurements up to > 1 MHz.
Fig. 4 depicts ACS measurements with
the fluxgate system on the multicore
MNP sample BNF-80 from Micromod for
temperatures between room temperature
and 70°C. As expected, the dc susceptibility decreases and the peak in the imaginary part shifts to higher frequencies
with increasing temperature. Similar
measurements were also performed with
the HF ACS system. Measured data taken
with both systems will be compared to
theory.
As a next step, temperature dependent
ACS measurements will be performed on
ferrogels (e.g., based on gelatine) and
more complex nanoparticles suspensions
provided by project partners.
Fig. 4: ACS spectra on multi-core MNP
sample measured for different frequencies.
Acknowledgments
Financial support by the DFG via
SPP 1681 (grant no. LU 800/4-1) is
acknowledged.
References
[1]
[2]
[3]
[4]
[5]
D. Eberbeck, F. Wiekhorst, U. Steinhoff, and
L. Trahms, J. Phys. D: Appl. Phys. 18, S2829
(2006).
F. Ludwig, E. Heim, M. Schilling, and K. Enpuku, J. Appl. Phys. 103, 07A314 (2008).
N.-S. Cheng, Industrial & Engineering Chemistry Research 47, 3285 (2008).
T. Wawrzik, T. Yoshida, M. Schilling, and F.
Ludwig, IEEE Trans. Magn. (accepted).
E. Roeben, L. Roeder, S. Tesch, M. Effertz, U.
K. Deiters, and A. M. Schmidt, Colloid. Polymer. Sci. 292, 2013 (2014).
35
Magnetic and temperature-responsive ferrogels
with low molecular weight gelators
S. Metzke1, J. Seliger1, S. Prévost1,2, M. Gradzielski1
1
Physikalische Chemie / Molekulare Materialwissenschaften, Institut für Chemie, Technische Universität Berlin,
Straße des 17. Juni 124. D-10623 Berlin.
2
Now at Soft Matter Structure, ESRF – The European synchrotron, 71 avenue des Martyrs, F-38000 Grenoble.
Thermoresponsive aqueous ferrogels,
where magnetic nanoparticles (NPs) are
incorporated in a self-assembled network
built by low molecular weight gelators,
are studied primarily by Small Angle
Scattering together with rheology and
magnetometry, to understand the interplay between the living network and NPs,
and enable control of the response to
mechanical stress and magnetic field.
A new class of gels discovered within this
project is based on mixing fatty acids
with basic amino-acids, with an emphasis
on oleic acid (C18:1COOH) and L-Arginine.
Such gels are eco-friendly, non-toxic and
cheap; they act intrinsically as pH buffer
and present attractive rheological and
temperature-dependent properties.
Background
Project
Using a silica shell to stabilize NPs in water, and creating the gel network via
self-assembly of small surfactant molecules that interacts with functionalized
NPs, enables the construction of more
elaborated ferrofluids that can quickly
respond to stimuli due to the small size
of the gelator that re-organizes immediately. Grafting amino-acids to the silica
shell allows to control the charge of NPs
and their interaction with the gel network
via H-bonds (strength and number of
junctions). Small Angle Scattering (SAS)
is used to get a detailed picture of the
arrangement of the particles and of the
gel fibers at the nanometer-scale while
Time-Resolved SAS will show the dynamics of such systems (relaxation time and
pathway of particles and network).
Figure 1: solutions at 300 mM oleic acid with 25
mM L-arginine steps. At 125 mM samples become
gels. Starting with 300 mM (equimolarity), gels are
transparent.
Scattered intensity
Factor 3 for each step of 25 mM arginine
Most ferrogels result from the addition in
large amounts of polymeric gelators to
an existing ferrofluid. [1] The resulting
ferrogels, at the colloidal scale, is in fact
composed of pockets or blobs of the
original ferrofluid encapsulated by large
beams of long polymer molecules. Such
systems do not exhibit any significant
synergistic response.
Wavevector / nm-1
Figure 2: SAXS data from ID02@ESRF, showing a
first transition from hydrated crystals to lamellar
phases at C18:1COOH:arginine 300:125, then crystalline packing of wormlikes at 300:300 onwards
(spectrum at equimolarity indicated in bold line).
The horizontal q-range covers 0.6-6 nm-1, corresponding in real space to ca. 1-10 nm.
Low molecular weight gelators
36
Nanoparticles
Timeline
Fe3O4 and CoO⋅Fe2O3 cubic NP of 12 nm
side have been obtained with narrow
dispersity, [2] an important parameter to
get the most out of scattering data. Synthesis of MnaZn1-aFe2O4 NPs is on-going,
to compare the dynamics of normal, hard
and soft ferrites. Due to epitaxial growth,
NPs are expected to have north / south
poles, as suggested by the alignment of
cubes on figure 3.
The project actively started with a PhD
student (SM) on February 1st 2014, who
is assisted by a Hi-Wi (JS).
The first 6 months have been devoted to
the synthesis of functionalized silicacoated monodisperse magnetic particles,
and the finding and characterization of
new gels optimized for this project. SAXS
and SANS experiments have been performed and 2 more are scheduled before
end of 2014 together with magnetometry
measurements at PTB.
In year 2 of the project (Feb. 2015 onward), dynamic SAS beam times will be
executed to probe the dynamics at the
nano-scale [4].
Acknowledgments
This work is supported by DFG PR1473/1
within the Priority Program SPP1681. The
original project leader Dr. Sylvain Prévost has been officially replaced by Prof.
Dr. Michael Gradzielski due to professional relocation.
References
Figure 3: TEM images of CoOFe2O3 cubic monodisperse particles of side 12 nm.
The coating by silica [3] is obtained by
reducing TEOS with arginine, thus resulting in NPs functionalized by amino acids.
Particles are water dispersible; the synthesis is currently being optimized to
reduce further the presence of clusters.
[1] M. Krekhova and G. Lattermann Journal of
Materials Chemistry vol. 18, no. 24, pp. 28422848, 2008.
[2] J. Park, K. An, Y. Hwang, J.G. Park, H.J. Noh,
J.Y. Kim, J.H. Park, N.M. Hwang, and T.
Hyeon Nature Materials vol. 3, no. 12, pp.
891-895, Nov. 2004.
[3] H. L. Ding, Y. X. Zhang, S. Wang, J. M. Xu, S.
C. Xu, and G. H. Li Chemistry of Materials vol.
24, no. 23, pp. 4572-4580, Dec. 2012.
[4] A. Wiedenmann, R. Gähler, R. P. May, U.
Keiderling, K. Habicht, S. Prévost, M. Klokkenburg, B. Erné, and J. Kohlbrecher in Studying Kinetics with Neutrons vol. 161, G.
Eckold, H. Schober, and S. E. Nagler, Eds.
Berlin, Heidelberg: Springer Berlin Heidelberg,
2009, pp. 241-263.
Figure 4: TEM images of Fe3O4@SiO2 NP with a 6
nm shell thickness.
37
Magneto-elastic behavior of super-paramagnetic
particle chains in a soft gel
Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
The elastic property of magnetic hybrid
materials can be controlled by applying a
magnetic field. It is essential to understand this magneto-elastic effect on a
single-particle level. Here we study the
magnetic field induced deformation of
super-paramagnetic particle chains in a
soft gel.
Figure 1. Sample cell and experimental setup.
The elastic network was obtained by hydrosilation of a difunctional vinylterminated polydimethylsiloxane (PDMS)
prepolymer with a SiH-containing crosslinker. A low-molecular-weight (770
g/mol) methyl-terminated PDMS was
used as solvent which carries the network and the super-paramagnetic particles. When the pre-polymer was crosslinking in the sample cell (about 160 microns height, see Figure 1) under a magnetic field of about 100 mT, the superparamagnetic particles aligned into
chains. The resulting gel with aligned
super-paramagnetic particle chains has
an elastic modulus lower than 10 Pa.
Laser scanning confocal microscope
(LSCM) was used to observe the chain
structure in the gel [1].
their morphology (Figure 2). Figure 3
shows that under a perpendicular magnetic field, short chains rotate to a certain angle, while the long chains become
buckled [2]. Under a higher magnetic
field or in a gel with lower elastic modulus, the rotation or buckled structures of
the super-paramagnetic particle chains
become more pronounced. However, the
wave length and amplitude are determined not only by magnetic field
strength and elastic modulus of the gel,
but also the length of the chains. Even
when the chain length is the same, different metastable states with different
number of undulations can be observed
in one sample under a perpendicular
magnetic field.
The rotation and buckled structures result from the magneto-elastic coupling.
Theoretical models will be developed and
compared to the experimental results
[2].
Figure 3. Super-paramagnetic particle chains in a
soft gel (<10 Pa) under a perpendicular magnetic
field. Image size=350×350 µm2. Short chains are
indicated by arrows.
Acknowledgments
Figure 2. Super-paramagnetic particle chains in a
soft gel under magnetic fields with different orientation angles. Image size=100×100 µm2.
The chains rotate or buckle under the
non-aligned magnetic field. As a function
of field orientation the chains change
38
We thank Peter Blümler, Andreas Menzel
and Peet Cremer for inspiring discussions
and acknowledge funding by the DFG
through the SPP 1681.
References
[1] M. Roth, C. Schilde, P. Lellig, A. Kwade, and G.
K. Auernhammer; Eur. Phys. J. E 35 (2012),
9801.
[2] S. Huang, P. Cremer, A. Menzel, G.K. Auernhammer; in preparation.
E. Roeben, L. Roeder, S. Teusch, M. Dörfer, L. Kibkalo,
M. Effertz, U. K. Deiters, A. M. Schmidt1
Department Chemie, Institut für Physikalische Chemie, Universität zu Köln, Luxemburger Str. 116, D-50939
Köln, email: annette.schmidt@uni-koeln.de
1
Motivation
Static and dynamic rheology is an established method for the investigation of the
flow and deformation properties of complex fluids like polymers.
In the context of nanostructured materials and composites, there is an increasing interest to determine the material
properties on the micro- or nanoscale
and experience the interaction between
the particles and the surrounding matrix.
Special interest is paid to the relative
size of the tracer particles and the structural length scale of the investigated material. In this respect, different tracer
particle-based microrheological methods
are developed, which have additionally
the advantage of a small sample volume,
enabling the exploration of the viscoelastic properties of soft matter which cannot
be produced in bulk quantities like biological polymers or living cells.[1]
Fig. 2: AC susceptometry of aqueous
polyethylene glycol solutions (Mn = 1000
g/mol-1) with different polymer concentration.
The resulting frequency-dependent complex susceptibility data is treated using
different theoretical approaches.[3]
Results and Discussion
Fig. 1: Magnetic Particle Nanorheology.
A tracer-free method is based on dielectric spectroscopy, relating the dielectric
function to the complex dynamic viscosity according to the Gemant-DiMarzioBishop model.[2]
Method
In the present work, we introduce a novel approach to investigate the nanorheological properties of soft materials by analyzing the dynamic response of magnetic nanoprobes exposed to an oscillating
magnetic field (AC susceptometry, Fig.
2). For this purpose we employ ferromagnetic CoFe2O4-nanoparticles as tracer particles in model systems based on
Newtonian fluids and aqueous solutions
of polyethylene glycol (PEG).
40
By adapting different methods including
an extended Debye relaxation model, a
modified
version of the GemantDiMarzio-Bishop model adapted to the
magnetic case and the Havriliak-Negami
equation, the experimental data can be
fitted to deliver frequency-dependent
rheological properties including viscosity
and loss moduli.
The approaches are verified experimentally for the case of Newtonian fluids of
various composition and viscosity, based
on ethylene glycol (EG) and triethylene
glycol (TEG) aqueous solutions.
Subsequently, the methods are applied
to systems with increasing complexity
with
respect
to
their
frequencydependent flow properties, while keeping
the chemical similarity. For this purpose,
we employ aqueous PEG solutions with
systematic variation of the concentration
and the molecular weight of the polymer.
By comparing the results with outcomes
of conventional rheology (Fig. 3), the va-
lidity and the limits of the nanorheological method are demonstrated [3]. The
resulting
data
on
the
frequencydependent shear modulus is interpreted
in the context of theories developed by
deGennes and Rubinstein on the sizedependence of particle diffusion in polymer solutions.[4]
Acknowledgments
Financial support is acknowledged from
DFG-SPP 1681 “Feldgesteuerte PartikelMatrix-Wechselwirkungen”.
References
[1]
[2]
[3]
[4]
[5]
C. Wilhelm, J. Browaeys, A. Ponton, J.-C.
Bacri, Physical Review E 67, 011504, 2003
E. A. DiMarzio, M. Bishop, J. Chem. Phys. 60,
3802-3811, 1974
E. Roeben, L. Roeder, S. Teusch, M. Effertz,
U. K. Deiters, A. M. Schmidt, Colloid Polym.
Sci., 292, 2013-2023, 2014
Cai L., Panyukov S., Rubinstein M. 44,
Macromolecules, 44, 7853–7863, 2011
B.J.B. Folmer, R.P. Sijbesma, R.M. Versteegen, J.A.J. van der Rijt, E.W. Meijer, Adv. Mater., 12, 874-878, 2000
Fig. 3: Frequency-dependent loss modulus G’’ as obtained from macrorheology
and calculated according to the modified
Gemant-DiMarzio-Bishop fit for PEG with
a molecular weight of 1000 g/mol.
Outlook
In upcoming experiments, we will further
increase the complexity of the sytems by
introduction of an additional polymer interaction mode. End-group functional
polymers with moieties that form dynamic, H-bond based bonds will be employed, (Fig. 4).[5] and the resulting dynamic properties will be investigated by
magnetic particle nanorheology. In addition, we will use traced particles with different surface functionalities in order to
obtain more information on the particlematrix interaction.
Fig. 4: Formation of supramolecular
structures by polymers bearing Hbonding end groups.
41
Investigation of rheological and dynamic properties of composites consisting of viscous hydrogels
and anisotropic hematite particles
A. Nack1, J. Seifert1, J. Wagner1
1
Universität Rostock, Institut für Chemie, Albert-Einstein-Straße 3a, D-18051 Rostock (Germany)
Composite materials as hydrogels with
embedded magnetic particles experienced a growing significance in modern
research. For instance in the field of biomedical applications ferrogels are discussed as suitable systems for remote
controlled drug release [1], [2] as well
as for the induction of local hypothermia
[3], [4].
Using the thermoresponsive crosslinked
hydrogel
poly-N-isopropylacrylamide
(pNIPAM) as a matrix, the properties of
composites with magnetic particles can
be influenced both by the temperature
and external magnetic fields. Due to a
characteristic coil-globuli transition the
interstitial space in the hydrogel network
accessible by the magnetic particles can
be controlled by the temperature as an
external parameter. Hereby the mobility
of the embedded shape- anisotropic
hematite particles, which are accessible
with aspect ratios 1 <
< 6, can be
changed. In addition to those particlenetwork interactions the orientational
distribution function of the elongated
particles can be influenced by the interaction with an external magnetic field
due to the difference in their friction coand their negative
efficients ∥ and
magnetic anisotropy which results in a
particle orientation perpendicular to the
applied magnetic field.
These dynamical properties of the composites at the mesoscale influence their
macroscopic, rheological behavior. In the
dependence on an external magnetic
field the viscosity and the complex shear
moduli are investigated at different temperatures. Dynamic properties of the
hydrogel matrix are investigated by
means of dynamic light scattering (DLS).
42
In Fig. 1, the increase of the relative visof a pNIPAM-hematite compocosity
site is displayed in dependence on the
magnetic flux density of an external
field. Due to the orientation of the particles perpendicular to the magnetic field
their rotational mobility is restricted. This
results in an increasing viscosity with
increasing flux density. At intermediate
flux density a nearly constant viscosity is
observed.
Fig. 1 Relative viscosity
of a pNIPAM-hematite
composite depending on an external magnetic field
for the temperatures 10°C, 15°C and 20°C measured with rotational shear at a constant shear rate
=20 s .
Fig. 2 shows field correlation functions g1
of a pNIPAM hydrogel for characteristic
resultvalues of the scattering vector
ing from a DLS measurement at 20°C.
Each correlation function shows a double
exponential decay which indicates the
coexistence of at least two different relaxation processes. These are classified
as - and -relaxation. Whereas the relaxation is related to the confined mo-
tion of a particle in the coordination cage
of its next neighbours, the -relaxation is
related to escape processes from the
coordination cages. The existence of two
relaxation processes is typical for nonergodic systems such as crosslinked hydrogels.
[2] J. Dobson. Magnetic nanoparticles for drug
delivery. Drug Developement Research, 67:55–60,
2006.
[3] L.L. Lao and R.V. Ramanujan. Magnetic and
hydrogel composite materials for hyperthermia
applications. Journal of Materials Science - Materials in Medicine, 15:1061–1064, 2004.
[4] Pol-Edern Le Renard, Olivier Jordan, Antonin
Faes, Alke Petri-Fink, Heinrich Hofmann, Daniel
Ruefenacht, Frederik Bosman, Franz Buchegger,
and Eric Doelker. The in vivo performance of magnetic particle-loaded injectable, in situ gelling,
carriers for the delivery of local hyperthermia.
Biomaterials, 31:691–705, 2010.
Fig. 2 Field autocorrelation functions g1( ) for a
pNIPAM hydrogel at different scattering vectors
at 20°C.
Further investigations address the nonlinear viscoelastic properties of the composites by means of Large Amplitude
Oscillatory Shear (LAOS) experiments.
Here the interpretation of the complex
shear modulus G* delivers information
about the elasticity of the network as
well an estimation of the mesh size of
the polymer network.
Acknowledgments
Financial support by the Deutsche Forschungsgemeinschaft in the framework
of the priority program SPP 1681 and by
the European Fond for Social Developement (EFRE) is acknowledged.
References
[1] N. Satarkar, J. Hilt. Magnetic hydrogel nanocomposites for remote controlled pulsatile drug
release. Journal of Controlled Release. 130:246251, 2008
43
Depolarized light scattering from anisotropic
particles: the influence of the particle shape on
the field autocorrelation function
C. Passow1, B. ten Hagen2, H. Löwen2, J. Wagner1
Universität Rostock, Institut für Chemie, Albert-Einstein-Straße 3a, D-18051 Rostock (Germany)
Heinrich-Heine-Universität Düsseldorf, Institut für Theoretische Physik II, Universitätsstraße 1,
D-40225 Düsseldorf (Germany)
1
2
Depolarized light scattering gives access
to the rotational as well as to the
translational diffusion of anisotropic
particles. Already one year after the
annus mirabilis of physics, in which
Einstein
published
his
work
on
translational diffusion [1], he described in
a second publication the rotational
diffusion of suspended particles [2]. The
latter process, however, is not observable
for spherical, isotropic objects.
The availability of defined anisotropic
particles, which are relevant for ferrogels,
enables the experimental access to
rotational
diffusion
by
means
of
depolarized
scattering
of
coherent
electromagnetic radiation as a probe. In
the presence, this technique is only
available for coherent visible light from
lasers, however, recent developments in
synchrotron radiation and free electron
lasers [3] enable the chance to use in the
future coherent X-rays with linear
polarization as a probe. Due to the
wavelength orders of magnitude smaller,
no limitation in the accessible Q-range
exists.
Here, the scattering functions for
depolarized scattering experiments are
calculated for solids of revolution of
different shape. The scattering functions
are expanded in spherical harmonics for
cylinders,
spherocylinders,
spindles,
double cones as model systems for
prolate solids of revolution and for oblate
solids of revolution additionally for lenses.
For anisotropic particles with axial
symmetry the depolarized scattering
function in VH-geometry, where the
polarization of the incident beam is
vertical and the one of the scattered
beam horizontal, reads as
with
denoting the orientation
averaged
translational
diffusion
coefficient.
is the difference
of the translational diffusion coefficients
for motions in the direction of the
symmetry axis and perpendicular and
C(Q,t) the coupling function. This function
is in the short-time limit expanded in
rotational invariants. Finally,
is the
rotational diffusion coefficient for the
rotation around an axis perpendicular to
the symmetry axis of the particles. The
coefficients
again are accessible
from the expansion of the scattering
function in rotational invariants. As a
consequence, both quantities,
and
strongly depend on the topology of
colloidal particles.
The
relaxation
of
the
depolarized
scattering function depends on the
translational and rotational diffusion
tensor of colloidal particles. For the here
investigated
axial
and
inversion
symmetric objects, the translational
and the
diffusion coefficients
and
rotational diffusion coefficient
for
rotations around the short axis are of
importance.
These
quantities
are
calculated employing bead models for the
solids [4] (Fig. 1).
Experimental access to the rotational
diffusion and the coupling function can be
obtained from the negative initial slope of
the field autocorrelation function, the first
cumulants
defined by
(2)
(1)
44
1
Fig. 1 Translational diffusion coefficients for spindles
and spherocylinders with an equatorial diameter of
in water (
).
In Fig. 2 and Fig. 3 the field
autocorrelation functions for depolarized
scattering experiments in VH-geometry
for spherocylinders and spindles, both
with
an
equatorial
diameter
of
are compared for the aspect
ratios
and
. The topology of
the particles influences already at small
scattering vectors the first cumulants, if
the long particle axis is comparable to the
wavelength.
Fig. 3 First cumulants in VH-geometry for
spherocylinders and spindles with an equatorial
diameter of
with an aspect ratio
of
.
The main contribution for the deviation
from the
behavior is the dependence
on the expansion coefficients
which
are the relative contributions to the
scattered intensity from the order l of the
expansion in rotational invariants.
The contribution from the coupling of
rotational and translational diffusion is
much smaller and even for comparatively
long objects only in the order of several
percent.
Acknowledgments
Financial support by the Deutsche
Forschungsgemeinschaft
in
the
framework of the priority program SPP
1681 is acknowledged.
References
[1]
[2]
[3]
Fig. 2 First cumulants in VH-geometry for
spherocylinders and spindles with an equatorial
diameter of
with an aspect ratio of
.
[4]
A. Einstein, Über die von der molekularkinetischen Theorie der Wärme geforderte
Bewegung von in ruhenden Flüssigkeiten
suspendierten Teilchen, Annalen der Physik
17, 549 (1905)
A. Einstein, Zur Theorie der Brownschen
Bewegung, Annalen der Physik 19, 371 (1906)
H. Deng, T. Zhang, L. Feng, C. Feng, B. Liu, X.
Wang, T. Lan, G. Wang, W. Zhang, X. Liu, J.
Chen, M. Zhang, G. Lin, M. Zhang, D. Wang,
Z. Zhao, Polarization switching demonstration
using crossed-planar undulators in a seeded
free-electron laser, Phys. Rev. ST Accel. Beams
17, 020704 (2014)
J. García de la Torre, G. del Rio and A. Ortega,
Improved calculation of rotational diffusion and
intrinsic viscosity of bead models for
macromolecules and nanoparticles, J. Phys.
Chem. B 111, 955-961 (2007).
45
2
Effects of the magnetization on the particle
structure of magnetorheological elastomers
Chair of Magnetofluiddynamics, Measuring and Automation Technology, Technische Universität Dresden
Introduction
Magnetorheological elastomers are a special kind of magnetic field-responsive
smart materials developed in the last
years, where magnetic micro particles are
embedded in a soft elastomer matrix. As
a result the magneotactive effects on the
mechanical properties are combined with
a stable, soft elastic material. The investigation of the interaction of the particles
with the external magnetic fields and the
matrix is a subject of ongoing research.
Computed X-ray micro tomography
proved to be a reliable method to investigate the particle structure of such composite materials [1, 2].
With the new kind of samples investigated
in this work, an effect of an external magnetic field on the orientation of NeFeB-microparticles was observed by means of
computed X-ray micro tomography.
evaluated. Volume and major axes were
calculated for each particle. The sample
was then magnetized using a Lake Shore
VSM, providing a magnetic field up to 2 T,
leading to a remanent magnetization of
the sample. The mechanical testing, the
tomography and the particle evaluation
was then repeated.
Material
Wacker silicone components and silicone
oil were used to produce the elastomer, in
which 35 wt% of highly anisotropic
shaped
Ne-Pr-Fe-Co-Ti-Zr-B-particles
MQP-S-11-9 by Magnequench were embedded. The average particle length is
40 µm. Due to the high size deviation,
particles with up to 150 µm were observed. The particles were coated with silicone oil to ensure proper linkage to the
elastomer matrix.
Methods
The polymerized samples were tested
with a DYNA-MESS universal testing machine with and without the presence of an
external magnetic field with a flux density
of 220 mT. Subsequently, the sample was
tomographed with the TomoTU cone
beam tomography setup. Figure 1 shows
a slice of the reconstructed tomography
data. 30,000 particles were separated and
46
Figure 1: Slice of the reconstructed tomography before magnetization showing the highly
anisotropic particles randomly oriented in the
sample.
Magnetorheological effect
The unmagnetized sample shows a significant increase of the elastic modulus in
presence of the magnetic field, proving
the soft magnetic behavior of the unmagnetized particles.
After magnetization the sample shows an
overall increase in stiffness and a significant increase of the effect of the external
magnetic field on the elastic modulus. The
results are visualized in the following figure 2.
Figure 2: The magnetorheological effect, induced by a 220 mT magnetic field, was calculated as a change of the elastic modulus of the
sample. Here the effect before and after magnetization with a 2T magnetic field is shown.
Particle structure
The angle between the longest major axis
of the highly anisotropic particles and the
direction of magnetization was calculated
from the evaluated geometry data for
every particle. It was shown, that the angle decreased due to the magnetization as
a result of particles rotating towards the
direction of magnetization to align themselves within the magnetic field. As a result of the elastic linkage between the
particles and the matrix no complete
alignment was observed. In figure 3 the
rotation of the particles is visualized
schamtically.
Figure 4: Mean value and standard deviation
of the angle between the direction of magnetization and the first major axis of the particle,
before and after magnetization.
Conclusion
A rotation of magnetized NeFeB-microparticles embedded in a silicone matrix
was observed by means of computed Xray micro tomography. This change in
particle structure may be linked to the
change in elastic properties of the sample
after magnetization.
Outlook
So far only 30,000 particles in one sample
were evaluated for this work. Future work
will include an investigation of a whole series of samples and a more detailed evaluation of the particle geometry data. Furthermore, a comparison with simulated
data of the mechanical behavior and the
particle structure will follow. A fine tuning
of the matrix material may lead to a
higher effect of particle structure change.
Acknowledgments
Financial support by DFG (Grant. No.
OD18/21) within SPP1681 is gratefully
acknowledged.
Figure 3: Rotation of a particle after magnetization decreasing the angle between the direction of magnetization and the first major axis
of the particle.
Figure 4 shows the change in the calculated angle. The error bars are the result
of the large distribution in orientation of
all particles. Despite the small change of
the mean value, the effect is significant
due to the fact, that both results were obtained with the very same sample.
References
[1]
[2]
Borbáth, T., Günther, S., Borin, D. Y., Gundermann, T., & Odenbach, S. (2012). Smart Materials and Structures, 21(10), 105018
Günther, D., Borin, D. Y., Günther, S., & Odenbach, S. (2012). Smart Materials and Structures, 21(1), 015005
47
Kinetic analysis of subsequent internalization of
magnetoliposomes in two different pancreatic
cancer cell types
I. Slabu1,2, A. Roeth3, T. Schmitz-Rode2, M. Baumann2,
D. Eberbeck1, L. Trahms1
Physikalisch-Technische Bundesanstalt, Berlin, Germany
Applied Medical Engineering, Medical Faculty, Helmholtz Institute, RWTH Aachen University, Germany
3
Department of General, Visceral and Transplant Surgery, RWTH University Hospital Aachen, Germany
1
2
Introduction
Magnetic nanoparticles are used as drug
carriers for therapy and as contrast
agents for diagnosis. For both applications, they are injected into the circulation and accumulated in tumor cells, but
also in cells of the reticuloendothelial
system. For sufficient accumulation in
the tumor and efficient detection of nanoparticles by imaging systems, the
mechanism of cell internalization must
be optimized. In this study, we investigate quantitatively the internalization of
magnetoliposomes (ML) in human pancreatic cancer cell lines (MiaPaCa and
BxPC3) as a function of time, in order to
understand the kinetics of cell nanoparticle interaction.
Materials and methods
ML were produced based on a method
developed in [1]. They consist of a superparamagnetic iron oxide core coated
by a phospholipid bilayer and an additional fluorescent phospholipid layer. The
physico-chemical properties of the used
ML are listed in
Table 1.
Table 1: Physico-chemical characteristics
of ML used for cell tests.
Crystalline structure
Fe3O4
Crystal diameter
(10 ± 3) nm
Hydrodynamic radius
(21 ± 1) nm
Saturation
(49.8 ± 0.8)
Am2/kg
magnetization
MiaPaCa and BxPC3 pancreatic cancer
cells were incubated in RMPI medium
and ML at 37 °C with an extracellular
concentration of 150 µg Fe/ml RMPI for
48
1 hour, 2 hours, 4 hours, 6 hours, 12
hours, and 24 hours, respectively.
The accumulated amount of ML in the
cells was determined with Magnetic Particle Spectroscopy (MPS). MPS is based
on the nonlinear part of the magnetic
susceptibility response of magnetic nanoparticles to an oscillating magnetic
field. MPS is a sensitive detection method that allows for the quantification of
the magnetic nanoparticle iron content
without being affected by cells or suspension medium.
Furthermore, the uptake of ML into the
cells was investigated by fluorescence
microscopy.
Results and discussion
An exemplary fluorescent microscopy
image is shown in Figure 1. The red color
in the image qualitatively illustrates
both, the ML binding at the cell membrane and the uptake of the ML into the
cell.
The ML uptake kinetics quantified with
MPS are displayed in Figure 2 and Figure 3 for BxPC3 cells and MiaPaCa cells,
respectively.
The ML internalization process into
BxPC3 cells shows an exponential behavior and is in line with the internalization
theory from literature [2] having a saturated mass of internalized ML of 31.4 pg.
For the investigated time slot of 12
hours, the ML internalization into MiaPaCa cells also shows an exponential
behavior, however with a much higher
ML affinity of MiaPaCa cells and a saturated mass of internalized ML of
111.7 pg. Moreover, the amount of internalized ML in MiaPaCa cells after 24
hours is not in line with the assumption
of an exponential behavior. This can be
explained by a higher proliferation rate
of the MiaPaCa cells. During cell division,
the ML load is equally shared by the
daughter cells. Therefore, the ML load
into cells must be scaled with the cell
division rate. The 24 hours ML load into
MiaPaCa cells indicates a doubling of the
cell number. A study concerning the proliferation behavior of MiaPaCa and BxPC3
cells is required, in order to determine
the number of cells capable of ML internalization after each time slot.
Figure 2: MPS quantification of ML internalization in BxPC3 cells as a function of
time t. m [pg] diyplays the iron load per
cell. The solid line corresponds to an exponential fit of the measured data.
Figure 3: MPS quantification of ML internalization in MiaPaCa cells as a function
of time t. m [pg] displays the iron load
per cell. The solid line corresponds to an
exponential fit of the measured data.
Figure 1: a) BxPc and b) MiaPaCa cells
incubated with fluorescent ML for 24
hours.
Acknowledgments
Conclusions
References
This work quantitatively demonstrates
that MiaPaCa and BxPC3 tumor cells behave differently with respect to ML internalization rate and internalization capacity, reflecting their functionality for a
therapeutic or diagnostic application.
Further investigations concerning the
high ML affinity of MiaPaCa cells are envisaged.
[1]
This work is supported by the DFG within
SPP 1681 No. TR408/8-1.
[2]
M. De Cuyper, P. Muller, H. Lueken, and
M. Hodenius, "Synthesis of magnetic
Fe3O4 particles covered with a modifiable
phospholipid coat," Journal of PhysicsCondensed Matter, vol. 15, pp. 1425S1436, 2003.
C. Wilhelm, F. Gazeau, J. Roger, J. N.
Pons, and J.-C. Bacri, "Interaction of
Anionic Superparamagnetic Nanoparticles
with Cells: Kinetic Analyses of Membrane
Adsorption and Subsequent
Internalization," Langmuir, vol. 18, pp.
8148–8155, 2002.
49
Magnetic Hybrid Materials for the Regenerative
Medicine: Synthesis, Simulation, Application and
toxicological Investigations
R.P. Friedrich1, P. Tripal1, J. Zaloga1, J. Nowak2, S. Odenbach2,
M. Liebl3, L. Trahms3, S. Lyer 1, C. Alexiou1
Department of Otorhinolaryngology, Head and Neck Surgery, Section for Experimental Oncology and Nanomedicine (SEON), Else Kröner-Fresenius-Stiftung-Professorship, University Hospital Erlangen, Glückstr. 10A,
91054 Erlangen.
2
Tecnical University University Dresden, Chair of Magnetofluiddynamics, Measuring and Automation Technology, George-Bähr-Str. 3, 01062 Dresden.
3
Physikalisch-Technische Bundesanstalt (PTB) Berlin, Medical Physics and Metrological Information Technology,
Biosignals, Biomagnetism., Abbestr. 2-12, 10587 Berlin
1
Introduction
Progress in the production of hybrid materials for tissue engineering and disease
models is mandatory for the development of modern therapy in the field of
regenerative medicine. Nanotechnology
offers the potential of circumventing the
shortage of available organs and the
likelihood of complications caused by
chronic immunosuppression as it allows
the 3-dimensional growth of autologous
tissues by magnetic cell seeding using
super-paramagnetic nanoparticles (SPIONs). Since nanoparticles can influence a
surrounding matrix when exposed to an
external magnetic field, nanotechnology
also provides us with therapeutic possibilities to cure a wide range of different
diseases or harmful conditions like
thrombosis.
Results
Production and Characterization of
SPIONs
We are continuously producing different
super-paramagnetic
nanoparticles
(SEONx,y,z) for various applications [1,2].
Especially stable SEONLA-BSA nanoparticles
are used for our work within the regenerative medicine [3]. We could verify
that the cellular uptake of SEONLA-BSA is
depending on the particle coating and
the solvent which in turn influence the
average size of the SEONLA-BSA agglomerates and the zeta potential in the cell
culture media.
To quantify the cellular SEONLA-BSA load,
we modified a recently published, photometric technique [4] and found a direct
50
correlation between the absorption at
370 nm and the cellular SEONLA-BSA
amount. As an accurate quantification of
cellular and cell-associated SPIONs is
crucial, we are currently performing a
comparative study between different
iron-quantification methods (UV/VIS,
MRX, FACS) together with partners from
the SPP1681.
Since a prerequisite for magnetic cell
seeding and tissue engineering is a low
SPION toxicity we monitored the viability
of SEONLA-BSA-loaded cells by measuring
cell proliferation and detected a measurable reduction only at very high
SEONLA-BSA concentrations. Additionally
there was no observable influence on
actin cytoskeleton architecture as shown
by immunocytochemistry. We additionally investigated the cellular uptake of nanoparticles and confirmed a direct correlation between the concentration of
SEON-NPs and incubation time. Moreover, cellular SEONLA-BSA colocalize with
lysosomal markers, suggesting a lysosomal degradation of the nanoparticles,
explaining the intracellular decrease of
SEONLA-BSA upon increased cultivation
time.
Development of arterial Scaffolds
using magnetic Cell Seeding
We modified the 3-dimensional cell seeding model [5] with HUVEC cells preloaded with SEONLA-BSA. As a proof of
principle for the production of tubular
endothelialized scaffolds we colonized
plastic tubes using the Vascucell Endothelizer, which allows magnetically controlled interactions between cells and
scaffold matrix. Cells loaded with
SEONLA-BSA show stable adhesion and
colonization to the tubular scaffolds.
Moreover, increased cultivation periods
caused a more dense coverage of the
tubes inner surface and proved the proliferation potential of magnetically seeded cells.
Fig. 2 Dissolution of blood clots. (A) Principle of an
in vivo thrombolysis model. (B) SPION penetration
into fibrin matrices using an in vitro thrombolysis
model.
Acknowledgments
Fig. 1 Endothelialization of arterial scaffolds. (A)
Principle of the endothelialization with magnetic
nanoparticles. (B) Artificial arterial scaffold model
magnetically seeded with human endothelial cells
(HUVEC). For better visualization cells were seeded
in stripes.
DFG SPP1681 (AL 552/5-1); DFG OD
18/23-1; EFI; FAU Erlangen-Nürnberg.
This method leads to a strong and homogeneous colonialization of the inner
surface of scaffolds without a noticeable
change in the viability of the cells.
Soon we will investigate the colonialization of scaffolds, currently used in medical centers as well as scaffolds produced
and modified by cooperation partners,
with one or more different cell layers.
[1]* Zaloga J, Janko C, Nowak J, Matuszak J,
Knaup S, Eberbeck D, Tietze R, Unterweger H,
Friedrich RP, Heimke-Brinck R, Reuter E, Cicha I, Dörje F, Odenbach S, Lyer S, Lee G,
Alexiou C. Development of a lauric acid
/albumin hybrid coated iron oxide nanoparticle system with improved biocompatibility. International Journal of Nanomedicine. In Press.
Interaction of magnetic Nanoparticles with fibrin-based Matrices
In this project we want to investigate
and optimize the behavior, properties
and alterations of different nanoparticles
and their corresponding corona after
magnetically assisted invasion or penetration of matrices. We are especially
interested in the interaction of nanoparticles and fibrin-based thrombi to find possibilities to treat thrombi without the
disadvantages of systemically applied
thrombolytica. In in vivo studies we have
already shown that drug-loaded SPIONs
can be magnetically directed to the location of interest [6]. In a similar way we
intend to deliver the therapeutics to
blood clots. We have now established a
first in vitro model for thrombosis which
will be used for the development and
investigation of different nanoparticles
with the potential to dissolve coagulated
blood.
References
[2]* Unterweger H, Tietze R, Janko C, Zaloga J,
Lyer S, Dürr S, Taccardi N, Goudouri OR,
Hoppe A, Eberbeck D, Schubert DW, Boccaccini AR, Alexiou C. Development and characterization of magnetic iron oxide nanoparticles
with a cisplatin-bearing polymer coating for
targeted drug delivery. International Journal
of Nanomedicine 2014:9 3659–3676.
[3]* Matuszak J, Zaloga J, Friedrich RP, Lyer S,
Nowak J, Odenbach S, Alexiou C, Cicha I. Endothelial biocompatibility and accumulation of
SPION under flow conditions. J of Magnetism
and Magnetic Materials. accepted.
[4]
Dadashzadeh ER, Hobson M, Bryant Jr LH,
Dean DD, Frank JA. Contrast Media Mol Imaging. 2013 ; 8(1): 50–56.
[5]
Perea H, Aigner J, Hopfner U, Wintermantel E.
Cells Tissues Organs. 2006; 183(3):156-65.
[6]
Tietze R, Lyer S, Dürr S, Struffert T, Engelhorn T, Schwarz M, Eckert E, Göen T,
Vasylyev S, Peukert W, Wiekhorst F, Trahms
L, Dörfler A, Alexiou C. Nanomedicine. 2013
Oct;9 (7):961-71.
* Granted by DFG SPP1681 (AL 552/5-1)
51
C. Gräfe1, F. Wiekhorst2, R. Müller3, A. Hochhaus1,
F. von Eggeling4,*, J.H. Clement1,*
1
Klinik für Innere Medizin II, Abteilung Hämatologie und Internistische Onkologie, Universitätsklinikum Jena,
Jena, Germany; joachim.clement@med.uni-jena.de
2
Physikalisch-Technische Bundesanstalt, Berlin, Germany
3
Leibniz-Institut für Photonische Technologien, Jena, Germany
4
Institut für Physikalische Chemie, FSU Jena und Klinik für Hals-, Nasen und Ohrenheilkunde, Uniniversitätsklinikum Jena, Jena, Germany; fegg@mti.uni-jena.de
Superparamagnetic iron oxide nanoparticles (SPIONs) are widely used for biomedical applications [1,2]. The introduction of SPIONs into a biological system
commonly means a direct interaction
with cellular structures, e.g. cells within
the blood stream, endothelial cells lining
the blood vessels or even epithelial cells
in underlying tissues. Thus, the process
of interaction of SPIONs with cells is a
fascinating research topic.
The aim of our project is to study and
understand the passage of coated SPIONs through cell layers driven by magnetic forces. Of special interest is the
interaction with the extracellular matrix,
the cell membrane as well as intracellular
lipid bilayers, e.g. endosomal/lysosomal,
mitochondrial or nuclear membranes.
Finally, the consequences of the interaction for the SPIONs as the formation of a
protein corona or the export out of the
cells are of interest.
We established an in vitro system for the
controlled and reproducible analysis of
nanoparticle-cell interactions based on
the transwell system with an optimal
pore size of 3 µm (figure 1). Human
brain microvascular endothelial cells
(HBMEC) were initially used to set up a
cell culture on the upper surface of the
transwell membrane. The firmness of the
monolayer was monitored by measuring
the trans-endothelial electrical resistance
(TEER) and application of sodium fluorescein to determine the permeability of
the HBMEC layer. A maximum density of
the monolayer was obtained after one
week of cultivation (figure 2). The vitality
of the cells was monitored by the Presto
blue assay [3]. The characteristics of the
monolayer are affected by the cell medium composition. Variations in the
52
amount of foetal bovine serum (FBS), as
well as the use of conditioned medium
change the properties of cell-cell contacts. The elucidation of the precise
mechanisms and its consequences for
nanoparticle-cell interactions needs further investigation.
Figure 1: Schematic experimental setup.
First incubations with SPIONS were performed with fluidMAG-D (chemicell
GmbH, Berlin) in a concentration range
from 0.5 to 100 µg/cm2 in the presence
of 10% FBS. Cells were incubated for 30
min on top of a permanent magnet (350
mT at the surface, field gradient at a
used distance from the magnet: 10 – 15
T/m) succeeded by additional 150 min
without magnet. The content of the upper compartment and the lower compartment were collected, each. The
membrane with the cell layer was removed and retained for further investigations. First quantitative analysis of the
solutions as well as the membranebound cells was done by magnetic particle spectroscopy [4]. We could show that
addition of 100 µg/cm2 fluidMAG-D
caused a more than 10-fold reduction of
iron content in the lower compartment in
the presence of HBMEC in comparison to
the uncovered membrane. A portion of
the applied SPIONs is detectable in
HBMEC. Fluorescent-labelled nanoparticles will help to identify the precise localization of these nanoparticles.
prepared by our collaboration partners
(S. Dutz, F. Schacher, A. Tschöpe, S.
Behrens, S. Mayr, chemicell GmbH). In
addition the nanoparticle content in the
two compartments as well as in the cellular fraction will be analysed for the distinct composition of its protein corona
with biochemical and spectroscopic techniques.
Acknowledgements
The perfect technical assistance of Cornelia Jörke is highly acknowledged. This
work was supported by Deutsche Forschungsgemeinschaft
(DFG)
in
the
framework of the priority program 1681
(FKZ: CL202/3-1).
References
[1]
Figure 2: Demonstration of a dense HBMEC
layer by ZO-1 staining.
ZO-1 (zona occludens 1) participates in cellcell contacts as a component of the tight
junctions. It is also involved in transcriptional
processes and therefore exhibits a nuclear
localization.
The aforementioned results encourage us
to use our experimental setup for the
parallel analysis of cell-nanoparticle interactions of a variety of nanoparticles
S. Dutz, J.H. Clement, D. Eberbeck, T. Gelbrich, R. Hergt, R. Müller, J. Wotschadlo, M.
Zeisberger, J. Magn. Magn. Mater. 2009, 321,
1501-1504.
[2] R. Sensenig, Y. Sapir, C. MacDonald, S. Cohen, B. Polyak, Nanomedicine 2012, 7, 14251442.
[3] F. Bähring, F. Schlenk, J. Wotschadlo, N.
Buske, T. Liebert, C. Bergemann, T. Heinze,
A. Hochhaus, D. Fischer, J.H. Clement, IEEE
T. Magn. 2013, 49, 383-388.
[4] N. Löwa, F. Wiekhorst, I. Gemeinhardt, M.
Ebert, J. Schnorr, S. Wagner, M. Taupitz, L.
Trahms, IEEE Trans. Magn. 2013, 49, 275278.
53
Fe3O4@Polydehydroalanine Hybrid Particles
M. von der Lühe1, A. Weidner2, U. Günther1, C. Gräfe3, S.
Dutz2,*, and F. H. Schacher1,*
1
Institut für Organische und Makromolekulare Chemie (IOMC) and Jena Center for Soft Matter (JCSM), Friedrich
Schiller Universität Jena, Germany; felix.schacher@uni-jena.de
2
Institute of Biomedical Engineering and Informatics (BMTI), Technische Universität Ilmenau, Ilmenau, Germany; silvio.dutz@tu-ilmenau.de
3
Klinik für Innere Medizin II, Abteilung Hämatologie und Internistische Onkologie, Universitätsklinikum Jena,
Jena, Germany
Once nanoparticles are brought into contact with biological systems, typically a
protein corona is formed immediately
around these particles. It is generally assumed that the composition and the
charge of any ligand shell present on the
"pristine" particles influence amount and
composition of the protein corona. Also,
this is supposed to have drastic influence
on the biocompatibility and the interactions of such nanoparticular systems with
the surrounding environment.[1, 2]
We are interested in investigating the influence of particle surface chemistry and
surface charge on formation and composition of the resulting protein corona after
incubation in biological fluids under different conditions. As an alternative to established shell materials, our work focuses on
the synthesis of a polymer shell with an
identical backbone and tunable charge
and/or charge distribution around superparamagnetic (single core, SPIONs) and
ferromagnetic (multi core) iron oxide nanoparticles. Starting from the dehydroalanine derivative 2-tert-butoxy-carbonylaminomethylacrylate (tBAMA), polymers
with molar masses of approximately
20,000 g/mol have been synthesized and
characterized.[3] By deprotection of either
one or both of the shielded functionalities
(-COOH and –NH2), these materials were
transformed into polycationic (poly(amino
methylacrylate),
PAMA),
polyanionic
(poly(tert-butoxycarbonylaminoacrylic
acid), PtBAA) or even polyzwitterionic
materials (polydehydroalanine, PDha,
Figure 1).
These materials were then used for coating of Fe3O4 nanoparticles (both single
and multicore (Figure 2), preparation
was done by alkaline precipitation) under
different conditions and the resulting
Fe3O4@polymer hybrid particles have
been characterized by dynamic light scat-
54
tering (DLS), transmission electron microscopy (TEM), zeta potential measurements, and vibrating sample magnetometry (VSM).
Figure 1: Fe3O4@polymer hybrid particles featuring
polymer shells of tunable charge.
We show that coating with PtBAA and
PDha was successful, as we found significant differences concerning dispersion behavior, size, surface charge and thermal
decomposition (TGA). As found in magnetic measurements, the magnetic properties of the core particles remain unchanged, suggesting that agglomeration
did not occur during the coating process.
Coating with PAMA, however, was only
partially successful up to now – mainly
due to solubility issues of the polymeric
material.
In ongoing studies the influence of different coating materials and parameters (incubation time, temperature, heating regime) on protein corona formation during
serum incubation of the Fe3O4@polymer
hybrid particles is investigated. Also, the
properties of the protein corona itself and
the biocompatibility of the corona-coated
nanoparticles are of interest and under investigation.
Figure 2: Typical TEM image of magnetic multicore
particles used for incubation studies.
Therefore, the obtained core/shell nanoparticles are incubated for a certain time
in a protein source (fetal calf serum
(FCS)) at different temperatures. The
temperature is controlled in two ways: either by magnetic heating (hyperthermia)
of the nanoparticles within FCS to generate a temperature gradient field or by
tempering the FCS in a water bath and
adding the nanoparticles to obtain a homogeneous temperature field.
Initial studies regarding the formation of
a protein corona under different conditions (15 min; 15, 37 and 50°C, heating
by hyperthermia and water bath) were
carried out using reference materials, i.e.
particles coated with either diethylaminoethyldextran (DEAE-dextran - positive
surface charge), dextran (neutral), or carboxymethyl-dextran (CM-dextran - negative surface charge). The solution properties of the nanoparticles like zeta-potential and hydrodynamic diameter were determined before and after the incubation.
Incubated nanoparticles were applied af-
terwards to a TBS polyacrylamide gradient gel under denaturating conditions and
protein bands were visualized by Coomassie blue staining. The effect of incubated particles on cell viability was tested
for human brain microvascular endothelial
cell line (HBMEC) with the PrestoBlue™
Cell Viability Assay.
Results show a dependence of the incubation temperature and way of heating on
the particles’ zeta potential as well as on
the composition of the protein corona.
The analysis of the electrophoretic mobility of the components of the protein corona indicate serum albumin and its derivatives as predominant proteins. The
nanoparticles, which were treated with
hyperthermia, contain a higher protein
load than those exposed to external heating. The investigated samples showed no
cytotoxic effect for the tested cell line.
Acknowledgments
This work was supported by Deutsche
Forschungsgemeinschaft (DFG) in the
framework of priority programme 1681
(FKZ: SCHA 1640/7-1, DU 1293/4-1,
CL202/3-1). FHS is grateful for financial
support from the Thuringian Ministry for
Education, Science, and Culture (TMBWK,
grants #B514–09051, NanoConSens and
#B515–10065, ChaPoNano).
References
[1]
[2]
[3]
S. Tenzer, D. Docter, S. Rosfa, A. Wlodarski, J.
Kuharev, A. Rekik, S. K. Knauer, C. Bantz, T.
Nawroth, C. Bier, J. Sirirattanapan, W. Mann,
L. Treuel, R. Zellner, M. Maskos, H. Schild, R.
H. Stauber, ACS Nano 2011, 5, 7155-7167.
P. del Pino, B. Pelaz, Q. Zhang, P. Maffre, G. U.
Nienhaus, W. J. Parak, Mater. Horiz. 2013, in
press (DOI: 10.1039/c3mh00106g)
U. Günther, L. V. Sigolaeva, D. V. Pergushov,
F. H. Schacher, Macromol. Chem. Phys. 2013,
214, 2202-2212.
55
Radiation optimized hydrogels and plasmasynthesized nanoparticles for magneticallycontrollable degradable bioactuators
E. I. Wisotzki1,2, M. Hennes1,3, M. Zink2 and S. G. Mayr1,2,3
Leibniz Institute of Surface Modification (IOM), Permoserstr. 15, 04318, Leipzig
Faculty of Physics and Earth Sciences, Leipzig University, Germany
3
Translational Center for Regenerative Medicine, Leipzig University, Germany
1
2
This project focuses on composites composed of magnetic core-shell nanoparticles (CS-MNP) and gelatin hydrogels for
the design of a biocompatible and biodegradable actuator. Here, plasma-assisted
inert gas condensation is used to synthesize MNP of various shapes, sizes and
structures [1,2]. These particles have the
potential to be embedded into gelatin
hydrogels, which are crosslinked using a
linear electron accelerator [4].
CS-MNP
Preliminary studies demonstrated the
ability of our plasma gas condensation
setup to synthesize Ni/Cu CS-NP with
typical diameters between 20 and 40 nm
using an additional coating chamber. In
the present work, heading for biocompatible and functionalizable nanoparticles, these results have been generalized
to the material system Ni/Au. Analyzed
particle populations exhibit strong homogeneity and monodispersity, with an Au
shell thickness of approximately 2 nm, as
demonstrated with HR-TEM and EDX.
These results are different from those
obtained using Cu as the shell material,
where bimodal distributions were observed and typical shell dimensions
found close to 10 nm [2].
Our experiments are complemented by
Monte Carlo simulations, which highlight
the metastable nature of the synthesized
CS-NP [3]. Still, at room temperature no
structural transformation of the particles
could be observed after more than 12
months storage. Finally, annealing studies show that the phase diagram of Ni/Cu
nanoparticles remains bulk-like, while in
Ni/Au an enhanced solubility of Au in Ni
was found.
Biocompatibility
We have shown that electron irradiation
can be used to tune the mechanical
properties and swelling behaviour of reagent-free gelatin hydrogels [4].
Figure 2: Average surface area of cells
one day after seeding.
Figure 1: EDX map of Ni/Au CS-MNP
56
To investigate biocompatibility, these
hydrogels were used as cell culture substrates for NIH 3T3 fibroblasts. Changes
to the surface area and shape factor (a
measure of circularity and spread) of the
cells were monitored using edge detection. It is often reported that cells have
larger surface area and lower shape factor (increased spread) on surfaces with
increasing stiffness [5]. During the 5-day
experimental period, cells proliferated on
all irradiated substrates. Figure 2 shows
the average surface area of cells on
10 wt% gelatin hydrogels.
while
investigating
the
magnetomechanical coupling between irradiated
gelatin hydrogels and embedded magnetic nanoparticles for the purposes of
designing a bioactuator prototype.
As expected, the cell surface area increased with substrate stiffness. However, very high doses of 60 to 100 kGy
appeared to reduce the cell area and
surface affinity. Other properties such as
contact angle and local elasticity are currently being investigated to better understand this discrepancy. Substrate
stiffness was confirmed by rheological
measurements done at 37°C after incubation in cell culture medium.
Acknowledgments
Thermal stability and degradation
Typically, gelatin has a sol-gel transition
temperature below 37°C. For biological
applications, this transition must be altered. The effects of electron irradiation
on the hydrogels’ thermal stability were
quantified by measuring the surviving gel
fraction after submersion in pure water
for 24 hours at 37°C. Furthermore, degradability was quantified by submerging
samples in simulated body fluid (SBF) at
37°C until breakdown, as shown in Figure 2. Samples with doses over 50 kGy
did not break down within the experimental time period of 44 days.
This project is funded by the German
Science Foundation (DFG), Priority Program (SPP) 1681.
References
[1]
R. Werner, T. Höche and S.G. Mayr, Cryst.
Eng. Comm. 13:3046, 2011.
[2]
M. Hennes, A. Lotnyk and S. G. Mayr,
Beilstein J. Nanotechnol. 5:466, 2014.
[3]
M. Hennes, J. Buchwald and S. G. Mayr,
Cryst. Eng. Comm. 14:7633, 2012.
[4]
E. Wisotzki, et al. J. Mater. Chem. B.
2:4297, 2014.
[5]
J. Solon, et al. Biophys. J. 93:4453, 2007.
Figure 3: 4 wt% gelatin remaining fraction of mass over time in SBF at 37°C.
Outlook
Present results demonstrate successful
synthesis of Au coated MNP as well as
biocompatible radiation optimized gelatin
hydrogels. Future studies aim for a complete characterization of the synthesized
CS-NP, especially with respect to their
magnetic properties and biocompatibility,
57
Actuator systems based on a controlled particlematrix interaction in magnetic hybrid materials
with application for locomotion and manipulation
I. Zeidis1, V. Böhm1, T. Kaufhold1, K. Zimmermann1,
V.A. Naletova2
Technische Universität Ilmenau, Department of Mechanical Enngineering, Technical Mechanics Group, MaxPlanck-Ring 12, 98693 Ilmenau, Germany
2
Lomonosov Moscow State University, Faculty of Mechanics and Mathematics, Leninskie Gory, 119992, Moscow, Russia
1
form of the body so the body may save
it’s new form (magneto-plastic effect).
0. Introduction
The paper deals with two aspects on the
development of actor systems based on
magnetic hybrid materials. In the first
part theoretical investigations concerning
the deformation of a magnetizable polymer in a magnetic field are presented.
The controlled deformation of hybrid materials is one of the basic tasks in the
design process of new actuators.
In the second part of the paper an overview of experimental results concerning
sensors and actuatiors using magnetorheological elastomers (MRE) is introduced.
1. Deformation of a body with a
magnetizable polymer in a magnetic
field
The deformation of various bodies with
magnetizable polymers was explored in
many works, see [1]. However, in these
researches usually there was one solution of a problem of statics only. In the
present project two problems are studied: the deformation of a spherical body
with a magnetizable polymer in an applied uniform magnetic field and the deformation of a thin cylindrical body with
a magnetizable polymer in an applied
non uniform magnetic field (Fig. 1).
The possibility of existence of more than
one form of the equilibrium of such bodies in the applied magnetic field is obtained. It’s mean that, for example, existence of the jumping (step-wise) modifications of the shape of a spherical body
and a hysteresis of the shape of a spherical body at a quasistatic change of magnitude of the applied uniform magnetic
field. In both case it’s mean that in an
applied magnetic field we can change the
58
undeformed
deformed
H
EM
PM
Fig. 1. Theoretically considered problems, PM/EM permanent/electro magnet.
2. Experimental work
Actuator systems for locomotion and
manipulation purposes are investigated
whereat the focus is on the interplay
between material deformations and the
mechanical motion in connection with the
issues of control and stability (Fig. 2).
Fig. 2. Basic configuration of a planar
locomotion system based on the asymmetric dynamic excitation of an MRE
structure.
For sensor applications, an MRE samples
based on carbonyl iron particles (particle
size: 6 µm, 16.5 Vol. %, BASF Co.), super conductive carbon particles (particle
size: 35 nm, 4.2 Vol. %, Printex XE2
Degussa Co.), silicon oil (44.2 Vol. %
PMX-200, Xiameter Co.), and PDMS elastomer (Sicovoss RF Soft, Voss Chemie
Co.) were prepared with the dimension
of 2x8x90 mm in the absence of a magnetic field. For sensor applications the
use of elastomer materials with embedded carbon particles is a common technique to detect mechanical deformations,
due to the change of their electrical
resistance.
First experimental results indicate, that
the electric resistance of the considered
MRE can also be changed with an applied
magnetic field without macroscopic deformation (Fig. 3), primairly due to the
particle matrix interactions inside the
material. The obtained effect enables the
realization of compliant pressure sensors
with tunable measurement range, using
non-structured MRE, as indicated in [2],
[3] using structured MRE.
Fig. 3. Measured change of the electrical resistance in dependence of the magnetic field
of the MRE sample over time.
Acknowledgments
This work is supported by Deutsche Forschungsgemeinschaft
(DFG)
project
ZI 540-17/1 and by the Russian Foundation for Basic Research (project 14-0191330).
References
[1]
[2]
[3]
Yu.L. Raikher, O.V. Stolbov. Magnetodeformation effect in a ferroelastic material. Technical Physics Letters. Vol. 26(2), 2000, pp.
156-158
I. Bica. Influence of the transverse magnetic
field intensity upon the electric resistance of
the magnetorheological elastomer containing
graphite microparticles. Materials Letters. Vol.
63(26), 2009, pp. 2230–2232
T.F. Tian, W.H. Li, Y.M. Deng. Sensing capabilities of graphite based MR elastomers.
Smart Mater. Struct. 20 (2011) 025022 (7pp)
59
Experimental strategies towards porous soft
magnetic composites
M. Krautz1, M. Schrödner2, J. Popp2, A. Waske1, J. Eckert1
1
2
IFW Dresden, Institute for Complex Materials, P.O. Box 270116, D-01171 Dresden, Germany
Thuringian Institute of Textile and Plastics Research e.V., Breitscheidstraße 97, D-07407 Rudolstadt, Germany
Soft magnetic polymer composites show
interesting mechanical properties that
can be manipulated by an external
magnetic field which makes them
suitable especially as actor or damping
materials. However, for flow control
application the architecture of such
composites is more complex. Here, open
porosity is needed as an additional
feature to ensure perfusion of a gaseous
or liquid medium. The channel width, and
hence the flow rate, can be controlled by
an external field (magnitude, tilt).
Our presentation comprises two aspects:
Fig. 1: Microscopic image of Polymer/Festrands with channel-like cavities.
a) The variation of the ratio between
magnetic particles and polymer matrix.
Here, different filling factors of shape
anisotropic
magnetic
fibres
are
investigated in terms of their structural
and magnetic properties, investigated by
tomography
and
magnetometry,
respectively.
Ideally,
shape-anisotropic
magnetic
fibers align as a chain parallel to the
extrusion direction (Fig. 2). Since the
Carbonyl-Fe particles are of isotropic
shape and homogeneously distributed in
the
strand,
further
materials
combinations will be investigated in
future.
b) The implementation of open porosity,
i.e. channels, into a particle/polymer
mixture. In a first step, place holders
have been inserted into a liquid polymer
and after curing the place holders, have
been removed. Since this did not lead to
satisfying results, a different, new
attempt has been tested in cooperation
with
the
TITK
e.V.
A
granular
thermoplastic polymer is intermixed with
Carbonyl-Fe particles and subsequently
extruded in form of strands with a
diameter up of about 50-100 µm. Theses
strands are bundled as shown in Fig. 1a.
The cavaties in between the cylindrical
strands can now be perfused by a
gaseous or liquid medium.
60
Fig. 2: Schematic arrangement of
polymer/ magnetic fibre - bundle for field
controlled flow application.
Acknowledgments
The present study is funded by the
German Research Foundation (DFG),
Priority Program SPP 1681.
Semi-industrial synthesis, characterization and
shaping of magnetosensitive elastomers focued
on compliant sensor manipulator applications
J. Popp1, M. Schrödner1
1
Thüringisches Institut für Textil- und Kunststoffforschung e.V., Abteilung Funktionspolymersysteme und Physikalische Forschung, Breitscheidstrasse 97, 07407 Rudolstadt
Magnetosensitive
elastomers
(MSE)
come with magnetomechanical effects,
such as deformation, reversibly changeable compliance and macroskopic magnetization for some [1,2,3].
Bridging the gap between the material
research on MSEs and the application of
the makroscopically working material
needs special care, since these compounds interweave complexly the diciplines.
Introduction
The authors consider the transition from
the laboratory scale to the ready-to-use
preshaped components of MSE with the
focus manipulator, sensor or actuator
systems [4]. The operation will be executed with semi-industrial processing.
As the process and facilities permit limited material properties commercially
available thermoplastic elastomers (TPE)
are used. For the aim of highly magnetic
field responsive MSEs µm-sized particles
suit best.
Preparation
Several TPEs have been tested with regard to finding a highly filled compound
with a high basic compliance, which is
supposed to decrease when magnetically
manulpulated, but still be sufficiently soft
for compliant manipulator/ sensor/ actuator devices. The employed particles are
a carbonyl iron powder (CIP) SQ by BASF
with an average diameter of 3.9 – 5.0
µm. Other type of particles are planned.
The processing contains the extrusion of
preblended TPE granulate and CIP, a
regranulation (if possible due to low TPE
viscosity) and melting for the finite shaping by spinning, extrusion or moulding.
Fibers with bicomponent cross sections
for pairing up differently behaving MSEs
are possible, too, see figure 1.
62
The double merging ensures a homogeneous particle distribution, see the x-ray
computer tomography in figure 2.
Fig
1:
Potential
shaping of MSEs.
Examples of different
bicomponent
cross section extrusion.
Fig. 2: XCT of an
MSE fiber: Desmopan + 40 wt 40%
CIP SQ. (measurement by Krautz
and Waske).
Characterization
The determination of the initial Young’s
modulus is performed with a uniaxial
tension testing machine Z005 by Zwick,
following closely the standards of DIN
53504 for reasons of comparison. Recent
results
compare
elastomer-particlecombinations listed in table 1.
TPE
Young’s
+ CIP
Modulus
[wt%]
[MPa]
Desmopan 481
(Bayer) + SQ
0
10,2
40
21,8
50
26,0
60
30,1
70
39,9
80
65,3
DynaFlex G6713
(PolyOne) + SQ
0
1,0
40
1,4
50
1,8
60
1,7
70
1,9
80
2,6
Tab. 1: Initial Young’s modulus
strain of MSE compounds.
Tear
strain
[%]
554
760
657
679
317
154
279
543
723
778
869
663
and tear
As an intermediate result, it can be stated Desmopan compounds are for compliant devices too hard, especially if an additional magnetical compiance adjustment is intended. DynaFlex compounds
possess a convenient softness. Other
MSEs employing TPE VersaFlex (by GLS)
and TF0STL (by Kraiburg) are even softer and thus, seem to be well suited for
compliant magnetically controlled applications. The testing is not concluded.
As the knowledge of the influence of the
magnetic field on the Young’s modulus is
essential, an appropriate magnetic system is in the process of design, yet. The
magnetic measurement facility will provide a homogeneous magnetic field parallel to the sample stroke with a strain of
100% and a maximum magnetic flux of
approximately 1T.
The presented MSEs hold in general a
relative permeability µ’ between 1.5 and
4.45, see figure 3.
In a cooperation with the team Zimmermann/Böhm, TU Ilmenau, this shall
bounded on a MSE gripper to serve as a
reversibly adjustable manipulation system with magnetically controlled sensitivity, figure 4.
Fig 4: Principle of an tactile gripper with
magnetically controlled reversible sensitivity made of MSE.
Acknowledgments
This work is supported by Deutsche Forschungsgemeinschaft (DFG). Additionally, the authors speak their thanks to M.
Krautz and Dr. A. Waske from IFW Dresden for the measurements with the XCT
as well as Dr. Ing. T. Ströhla from TU
Ilmenau, Dept. Mechatronics for the concept of the magnetic system and the
magnetic field simulation.
References
[1]
[2]
Fig 3: Relative permeability of
(Desmopan + CIP SQ)
MSE
[3]
Conclusion and Preview
[4]
The research for further suitable TPE
matrizes also in interaction with other
types of particles has to be proceeded.
The beginning characterization will be
more densified by testing the magnetomechanical tension behavior including
the investigation of the load-historybehavior (Mullin effect) and also the dynamic properties within the upcoming
month.
Parallel to this part, the preparation for
the material implementation for a tactile
contact area will start with the tests on
material and geometry dependent compliance of extruded fiber segments when
charged by pressure load.
Coquelle E, Bossis G, Szabo D, Giulieri F:
Micromechanical analysis of an elastomer
filled with particles organized in chain-like
structure, 2006 Journal of Materials Science
41 (18) pp 5941-5953
Varga, Z.; Filipcsei, G.; Zrínyi, M.: Magnetic
Field Sensitive Functional Elastomers with
Tuneable
Elastic
Modulus.
Polymer,
47(2006)1, 227-233
G.Stepanov, D.Borin and S.Odenbach, Magnetorheological effect of magneto-active elastomers containing large particles, J. Phys.:
Conf. Ser. 149 (2009) 012098
Kaufhold T, Böhm V, Zimmermann K: Design
of a miniaturized locomotion system with variable mechanical compliance based on amoeboid movement. 2012 4th IEEE RAS & EMBS
International Conference on Biomedical Robotics and Biomechatronics (BioRob) pp 10601065
63
List of Participants
Christoph Alexiou
Sylvio Dutz
Maria Krautz
HNO-Klinik Erlangen, SEON, Waldstr. 1,
91054 Erlangen
Tel.: 09131-85 33142
E-mail: c.alexiou@web.de
TU Ilmenau
Gustav-Kirchhoff-Straße 2
98639 Ilmenau
Tel.: 03677-69 1959
E-mail: silvio.dutz@tu-ilmenau.de
IfW Dresden, Helmholtzstr. 20, 01069
Dresden
Tel.: 0351-465 9669
E-mail: m.krautz@ifw-dresden.de
Ingo Appel
Karlsruhe Institute of Technology,
Hermann-von-Helmholtz-Platz 1, 76344
Eggenstein-Leopoldshafen
Tel.: 0721-608 24119
E-mail: ingo.appel@kit.du
Abdolhamid Attaran
TU Dresden, Institut für
Festkörpermechanik, 01062 Dresden
Tel.: 0351-463 33401
E-mail: abdolhamid.attaran@tudresden.de
Günther Auernhammer
Max-Planck-Institut für
Polymerforschung, Postfach 3148, 55021
Mainz
Tel.: 06131-379 113
E-mail: auhammer@mpip-mainz.mpg.de
Sebastian Backes
TU Berlin, Institut für Chemie, 10623
Berlin
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Silke Behrens
Karlsruher Institut für Technologie,
Postfach 3640, 76021 Karlsruhe
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Kerstin Birster
Universität des Saarlandes, Technische
Physik, 66123 Saarbrücken
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E-mail: kerstin@birster.de
Valter Böhm
Technische Universität Ilmenau,
Technische Mechanik, Max-Planck-Ring
12, 98693 Ilmenau
Tel.: 03677-692 2478
E-mail: valter.boehm@tu-ilmenau.de
Joachim Clement
Universitätsklinikum Jena, Erlanger Allee
101, D-07747 Jena
Tel.: 0049-3641 9325820
E-mail: joachim.clement@med.unijena.de
Peet Cremer
Universität Düsseldorf, Institut für
Theoretische Physik II, Universitätsstr. 1,
40225 Düsseldorf
Tel.: 0049-211 8112055
E-mail: Pcremer@thphy.uniduesseldorf.de
64
Dietmar Eberbeck
PTB Berlin, Abbestr. 2 - 12, 10587 Berlin
Tel.: 030-34817 208
E-mail: dietmar.eberbeck@ptb.de
Alexey Eremin
Otto-von-Guericke-Universität,
Universitätsplatz 2, 39106 Magdeburg
Tel.: 0391 6720099
E-mail: alexey.eremin@ovgu.de
Yong Geng
Tel.: 0391-67 58169
E-mail: gengyong09@gmail.com
Christine Gräfe
Uniklinikum Jena, Erlanger Allee 101,
07747 Jena
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Marcel Hennes
Leibniz-Institut für
Oberflächenmodifizierung, Permoserstr.
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E-mail: marcel.hennes@iom-leipzig.de
Christian Kuhlmann
TU Braunschweig, Institut für elektr.
Messtechnik, Hans-Sommer-Str. 66,
38106 Braunschweig
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E-mail: c.kuhlmann@tu-bs.de
Joachim Landers
Universität Duisburg-Essen, Aktienstr.
72, 45473 Duisburg
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E-mail: joachim.landers@uni-due.de
Michael Lentze
Deutsche Forschungsgemeinschaft DFG,
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Manfred Lücke
Universität des Saarlandes, Theoretische
Physik, Postfach 15 11 50, 66041
Saarbrücken
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E-mail: luecke@lusi.uni-sb.de
Frank Ludwig
TU Braunschweig, EMG, Hans-SommerStr. 66, 38106 Braunschweig
Tel.: 0531 3913863
E-mail: f.ludwig@tu-bs.de
Christian Holm
Stefan Lyer
Institute for Computational Physics,
University of Stuttgart
Allmandring 3
70569 Stuttgart
Tel.: 0711-6856 3701
E-mail: christian.holm@icp.unistuttgart.de
HNO-Klinik Erlangen, SEON, Waldstr. 1,
91054 Erlangen
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E-mail: stefan.lyer@uk-erlangen.de
Shilin Huang
Mainz
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E-mail: huangs@mpip-mainz.mpg.de
Markus Kästner
Institut für Festkörpermechanik, TU
Dresden
01062 Dresden
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E-mail: markus.kaestner@tu-dresden.de
Sabine Klapp
TU Berlin, Institut für Theoretische
Physik, Hardenbergstr. 36, 10623 Berlin
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E-mail: Klapp@physik.tu-berlin.de
Stefan Mayr
15, 04318 Leipzig
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Andreas Menzel
Heinrich-Heine-Universität Düsseldorf,
Universitätsstr. 1, 40225 Düsseldorf
Tel.: 0211-81 12056
E-mail: menzel@thphy.uniduesseldorf.de
Sarah Metzke
Technische Universität Berlin
Straße des 17. Juni 124, Sekr. TC7
10623 Berlin
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E-mail: s.metzke@tu-berlin.de
Robert Müller
Felix Schacher
Andreas Tschöpe
IPHT Jena, A.-Einstein-Str. 9, 07745
Jena
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E-mail: robert.mueller@ipht-jena.de
IOMC, Friedrich Schiller Universität Jena
Lessingstraße 8
07743 Jena
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E-mail: felix.schacher@uni-jena.de
Universität des Saarlandes,
Experimentalphysik, D-66123
Saarbrücken
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E-mail: antsch@mx.uni-saarland.de
Annette Schmidt
Sylvia Türk
Universität Köln, Chemistry Department,
Luxemburger Str. 116, 50939 Köln
Tel.: 0221-470 5410
E-mail: Annette.Schmidt@uni-koeln.de
Strömungsmechanik, Lehrstuhl für
Magnetofluiddynamik/MAT, 01062
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Annemarie Nack
Universität Rostock, Dr. Lorenz Weg 1,
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Stefan Odenbach
Dresden
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Christopher Passow
18059 Rostock
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Stavros Peroukidis
TU Berlin, Institut für Theoretische
Physik, Hardenbergstr. 36, 10623 Berlin
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Giorgio Pessot
Heinrich-Heine-Universität Düsseldorf,
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Harald Pleiner
Mainz
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Jana Popp
TITK e. V. Breitscheidstr. 97, 07407
Rudolstadt
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E-mail: jana.popp@tu-ilmenau.de
Hilke Remmer
Inst. für El. Messtechnik
TU Braunschweig
Hans-Sommer-Straße 66
38106 Braunschweig
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E-mail: h.remmer@tu-bs.de
Eric Roeben
Universität Köln, Chemistry Department,
Luxemburger Str. 116, 50939 Köln
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E-mail: eroeben@uni-koeln.de
Christoph Schopphoven
Universität des Saarlandes, Technische
Physik, 66123 Saarbrücken
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E-mail: christoph@schopphoven.de
Mario Schrödner
TITK e. V. Breitscheidstr. 97, 07407
Rudolstadt
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E-mail: schroedner@titk.de
Malte Schümann
Dresden
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E-mail: malte.schuemann@tudresden.de
Jan Seliger
TU Berlin, Sekretariat TC7, 10623 Berlin
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E-mail: jan.seliger@gmx.de
Ioana Slabu
Tel.: 030-3481 7411
E-mail: iona.slabu@ptb.de
Christian Spieler
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Ralf Stannarius
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Moritz von der Lühe
IOMC, Friedrich Schiller Universität Jena
Lessingstraße 8
07743 Jena
Tel.: 03641 948287
E-mail: moritz.von-der-luehe@unijena.de
Joachim Wagner
18059 Rostock
Tel.: 0381-498 6512
E-mail: joachim.wagner@uni-rostock.de
Thomas Wallmersperger
Tel.: 0351-463 37013
E-mail: thomas.wallmersperger@tudresden.de
Andreas Weidner
TU Ilmenau
Gustav-Kirchhoff-Straße 2
98639 Ilmenau
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E-mail: andreas.weidner@tu-ilmenau.de
Heiko Wende
Universität Duisburg-Essen, Lotharstr. 1,
47057 Duisburg
Tel.: 0203-379 2838
E-mail: heiko.wende@uni-due.de
Emilia Wisotzki
15, 04318 Leipzig
Tel.: 0341-235 2688
E-mail: emilia.wisotzki@iom-leipzig.de
Marcus Witt
Matthias Taupitz
Charité Berlin, Institut für Radiologie,
Campus Charité Mitte, Charitéplatz 1,
10117 Berlin
Tel.: 030-8445 3041
E-mail: matthias.taupitz@charite.de
TU Berlin
Schmiljanstraße 13
12161 Berlin
Tel.: 030-314 29887
E-mail: M.Witt@tu-berlin.de
Igor Zeidis
Lutz Trahms
Tel.: 0049-30 34817213
E-mail: lutz.trahms@ptb.de
12, 98693 Ilmenau
Tel.: 03677-692 2478
E-mail: igor.zeidis@tu-ilmenau.de
65
Mengbo Zhou
Friedrich Schiller Universität Jena
Humboldt Straße 9
07743 Jena
0176-63367309
E-mail: mengbo.zhou@uni-jena.de
Klaus Zimmermann
12, 98693 Ilmenau
Tel.: 03677-692 2478
E-mail: klaus.zimmermann@tuilmenau.de
66

matrix interaction in magnetic hybrid materials with application for

Transcription

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