12. July 2011
Ellipsoidal Hybrid Magnetic Microgel
Particles with Thermally Tunable Aspect
Ratios
Hervé Dietsch,
Particles 2011 Conference 9-12 July 2011
Adolphe Merkle Institute
Université de Fribourg
Rte de l‘Ancienne Papeterie 3
CH-1723 Marly
T +41 26 300 91 37
F +41 26 300 97 47
herve.dietsch@unifr.ch
www.am-institute.ch
Functionalized Building Blocks:
Colloids, Polymers, Surfactants
Building
Blocks
Particles 2011 conference
Interactions,
Phase Behavior,
Microstructure
Stimuli-Responsive Particles
Temperature,
Soft
Materials
Structures
Magnetic field,
Light,
pH,
Properties
Molecule to be
detected,
Protein…
and Particle Assemblies
Particle-particle interactions
Particle-solvent interactions
Eventually as a function of
the used stimulus
I 12. July 2011 I p. 2
Crystallization,
Phase
Separation,
Gelation
Nanostructured Materials
-> Novel Properties:
Thermoresponsive particles: LCST and VPTT
Microscopic scale
Example: PNIPAM a thermosensitive polymer
Microgel behavior
Linear chain
microgel
(network)
good solvent
=> swollen
soft shell
T<LCST
T>LCST
LCSTPNIPAM~33°C
Low Critical Solution Temperature
VPTT
Volume Phase Transition Temperature
I 12. July 2011 I p. 3
H2O
Tc≈33ºC
poor solvent
=> collapsed
hard sphere
H2O
Thermoresponsive particles: LCST and VPTT
Microscopic scale
Example: PNIPAM a thermosensitive polymer
Microgel behavior
Size, volume fraction
and
Interactions control
One single trigger: Temperature
Linear chain
microgel
(network)
good solvent
=> swollen
soft shell
T<LCST
T>LCST
LCSTPNIPAM~33°C
Low Critical Solution Temperature
VPTT
Volume Phase Transition Temperature
I 12. July 2011 I p. 4
H2O
Tc≈33ºC
poor solvent
=> collapsed
hard sphere
H2O
Another Stimulus and morphology:
Ellipsoidal-shaped Magnetic Particles
a
Submicrosized 80nm<a<150nm
 3
 6
Without
phosphate ions
Isotropic
particle
Matijevic et. al. 1978
I 12. July 2011 I p. 5
Ocaña et. al. 1999
Alternative: Tuning the aspect ratio by silica coating
TEOS
in H2O
I 12. July 2011 I p. 6
in Ethanol
NH3
Based on Graf et. al. 2003
Alternative: Tuning the aspect ratio by silica coating
TEOS
in H2O
I 12. July 2011 I p. 7
in Ethanol
NH3
Based on Graf et. al. 2003
Morphology characterization using SAXS and TEM
uncoated
13 nm silica
30 nm silica
59 nm silica
M. Reufer, HD et al., J. Phys. Chem. B, 2010, 114, 4763–4769.
I 12. July
2011 magnetic
I p. 8
More
about
properties: M. Reufer, HD et al., J Phys. Cond. Matter, 2011, 23,065102.
Control of the surface chemistry thanks to the silica layer
R'
R'
O
HO
OH
silane agent
OH
O
R'
S i
S i
O
S i
O
O
O
O
R'
HO
HO
S i
OH
OH
OH
O
O
S i
R'
R'
O
O
O
R
O
O
S i
S i
S i
R
R'
Si
O
O
R'
R
H3C
R'
O
O
CH2
H3C
Si
O
O
O
CH3
CH3
silane agent
Surface modification
I 12. July 2011 I p. 9
+ H-R
Hybrid combination with the thermoresponsive PNIPAM shell
Monomer,
cross-linker,
initiator, Δ
Reactive silane on
the surface
Precipitation
polymerization
H2C
O
HN
CH3
H3C
NIPAM
α-Fe2O3/PNIPAM
C. Dagallier,
H.2011
Dietsch*,
I 12. July
I p. 10 P. Schurtenberger and F. Scheffold, Soft Matter, 2010, 6(10): 2174-2177
Temperature response and dynamical arrest
[nm]
RRh [nm]
DLS
550
120
500
450
100
400
80
350
300
60
250
40
200
Rb2
Rb1
V
Rh 0.03M NaSCN
Rh
Ra
T
15°C Rb1
Φ
15 15 20 20 25 25 30 30 35 35 40 40 45
TT [°C]
[°C]
Hydrodynamic
Hydrodynamic radius
radius of
of hematite-PNIPAM
PNiPAM microgel
core-shell vs.
particles
vs. temperature.
temperature.
Rb1>Rb2>Ra
I 12. July 2011 I p. 11
V
30°C Rb2
Probing the rotation of hybrid microgels
Pre-alignment
Setup
(Microscope)
Direction of
Light beam
35°C

35°C
B

B

10°C
B
birefringent
10°C
Experiment: temperature ramp
P
CCD
A
P

H
I 12. July 2011 I p. 12
A
Probing the rotation of hybrid microgels
Pre-alignment
Setup
(Microscope)
Direction of
Light beam
35°C

35°C
B

B

10°C
B
birefringent
10°C
Experiment: temperature ramp
P
CCD
A
P

H
I 12. July 2011 I p. 13
A
Properties of the hybrid microgels
PNIPAM microgels
Hematite particles
C. Dagallier,
H.2011
Dietsch*,
I 12. July
I p. 14 P. Schurtenberger and F. Scheffold, Soft Matter, 2010, 6(10): 2174-2177
Properties of the hybrid microgels
Size, volume fraction,
Interactions control,
PNIPAM microgels
Optical
anisotropy, magnetic orientation control
Two triggers: Temperature and Magnetic field
Hematite particles
C. Dagallier,
H.2011
Dietsch*,
I 12. July
I p. 15 P. Schurtenberger and F. Scheffold, Soft Matter, 2010, 6(10): 2174-2177
Remaining challenges
• Increase the magnetic response
Hematite are canted-antiferromagnetic
• Orientation under magnetic field along the long axis


y
• Morphology changes with temperature
T
I 12. July 2011 I p. 16

x
H
y

z
H
Conclusion
•
Particles with a proper surface chemistry can be incorporated in a microgel (or
another polymer shell or bulk) if used as seeds.
•
Magnetic responsive can be tailored by control of the crystalline structure
•
Combining two stimuli can lead to more than 2 new properties (magnetic and
thermosensitive can lead also to morphology mutation and polarization of light, Xray…)
Can be used for rotation diffusion, friction, glass transition, phase diagrams, orientationna
relaxation in dense microgel suspensions, active microrheology studies…
I 12. July 2011 I p. 17
The Group
Liliane Ackermann
Adriana Mihut
Shuo Bai
Camille Dagallier (Stanford)
Verena Staedele (PSI)
Ann Hirt (ETHZ)
Urs Gasser (PSI)
Stefan Hengsberger(EIF)
Frank Scheffold (UniFr)
Peter Schurtenberger (ULund)
Funding
Izabela Bobowska
I 12. July 2011 I p. 18
Olivier Pravaz
Jérôme Crassous