Ellipsoidal Hybrid Magnetic Microgel Particles with Thermally - - PowerPoint PPT Presentation

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 Adolphe Merkle Institute

• 12. July 2011

Ellipsoidal Hybrid Magnetic Microgel Particles with Thermally Tunable Aspect Ratios

Hervé Dietsch, Particles 2011 Conference 9-12 July 2011

I 12. July 2011 I p. 2

Functionalized Building Blocks: Colloids, Polymers, Surfactants

Properties Building Blocks Structures

Soft Materials

Interactions, Phase Behavior, Microstructure Nanostructured Materials

• > Novel Properties:

Crystallization, Phase Separation, Gelation

and Particle Assemblies Particle-particle interactions Particle-solvent interactions Eventually as a function of the used stimulus Stimuli-Responsive Particles Temperature, Magnetic field, Light, pH, Molecule to be detected, Protein…

Particles 2011 conference

I 12. July 2011 I p. 3

Thermoresponsive particles: LCST and VPTT

Example: PNIPAM a thermosensitive polymer Linear chain microgel

(network)

Microscopic scale T<LCST T>LCST

LCSTPNIPAM~33°C Low Critical Solution Temperature VPTT Volume Phase Transition Temperature

good solvent => swollen poor solvent => collapsed

H2O H2O

Tc≈33ºC soft shell hard sphere

good solvent => swollen poor solvent => collapsed

H2O H2O H2O H2O

Tc≈33ºC soft shell hard sphere

Microgel behavior

I 12. July 2011 I p. 4

Thermoresponsive particles: LCST and VPTT

Example: PNIPAM a thermosensitive polymer Linear chain microgel

(network)

Microscopic scale T<LCST T>LCST

LCSTPNIPAM~33°C Low Critical Solution Temperature VPTT Volume Phase Transition Temperature

good solvent => swollen poor solvent => collapsed

H2O H2O

Tc≈33ºC soft shell hard sphere

good solvent => swollen poor solvent => collapsed

H2O H2O H2O H2O

Tc≈33ºC soft shell hard sphere

Microgel behavior

Size, volume fraction and Interactions control One single trigger: Temperature

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Without phosphate ions Isotropic particle

3   6  

Another Stimulus and morphology: Ellipsoidal-shaped Magnetic Particles

Matijevic et. al. 1978 Ocaña et. al. 1999

Submicrosized 80nm<a<150nm

a

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Alternative: Tuning the aspect ratio by silica coating

NH3 in H2O in Ethanol TEOS

Based on Graf et. al. 2003

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Alternative: Tuning the aspect ratio by silica coating

NH3 in H2O in Ethanol TEOS

Based on Graf et. al. 2003

I 12. July 2011 I p. 8

uncoated 13 nm silica 30 nm silica 59 nm silica

• M. Reufer, HD et al., J. Phys. Chem. B, 2010, 114, 4763–4769.

More about magnetic properties: M. Reufer, HD et al., J Phys. Cond. Matter, 2011, 23,065102.

Morphology characterization using SAXS and TEM

I 12. July 2011 I p. 9

Control of the surface chemistry thanks to the silica layer

silane agent

Si R' R R R

HO OH OH OH OH HO HO OH

+ H-R

S i O S i O S i O S i O S i O S i O S i O S i O O O O O O O O O R' R' R' R' R' R' R' R'

silane agent Surface modification

Si O CH3 CH2 O O C H3 O C H3 O CH3

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Monomer, cross-linker, initiator, Δ Reactive silane on the surface Precipitation polymerization α-Fe2O3/PNIPAM

C H2 O N H CH3 C H3

NIPAM

Hybrid combination with the thermoresponsive PNIPAM shell

• C. Dagallier, H. Dietsch*, P. Schurtenberger and F. Scheffold, Soft Matter, 2010, 6(10): 2174-2177

I 12. July 2011 I p. 11

Hydrodynamic radius of PNiPAM microgel

• vs. temperature.

15 20 25 30 35 40 40 60 80 100 120

R [nm] T [°C]

Rh 0.03M NaSCN Rh

Rb1 Rb2 Ra Rb1>Rb2>Ra

DLS

15 20 25 30 35 40 45 200 250 300 350 400 450 500 550

Rh [nm] T [°C]

Hydrodynamic radius of hematite-PNIPAM core-shell particles vs. temperature. Rb1 Rb2 Ra

DLS

T Φ V V 30°C Rb2 15°C Rb1

Temperature response and dynamical arrest

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Probing the rotation of hybrid microgels Experiment: temperature ramp Pre-alignment



B

(Microscope)



B

35°C 35°C 10°C 10°C

Setup

 



B

Direction of Light beam

birefringent CCD



H

P A P A

I 12. July 2011 I p. 13

Probing the rotation of hybrid microgels Experiment: temperature ramp Pre-alignment



B

(Microscope)



B

35°C 35°C 10°C 10°C

Setup

 



B

Direction of Light beam

birefringent CCD



H

P A P A

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Properties of the hybrid microgels

Hematite particles PNIPAM microgels

• C. Dagallier, H. Dietsch*, P. Schurtenberger and F. Scheffold, Soft Matter, 2010, 6(10): 2174-2177

I 12. July 2011 I p. 15

Properties of the hybrid microgels

Hematite particles PNIPAM microgels

• C. Dagallier, H. Dietsch*, P. Schurtenberger and F. Scheffold, Soft Matter, 2010, 6(10): 2174-2177

Size, volume fraction, Interactions control, Optical anisotropy, magnetic orientation control Two triggers: Temperature and Magnetic field

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Remaining challenges



H



H

z y x y





• Orientation under magnetic field along the long axis
• Increase the magnetic response

Hematite are canted-antiferromagnetic

• Morphology changes with temperature

T

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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, X- ray…)

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. 18

The Group

Liliane Ackermann Adriana Mihut Shuo Bai Jérôme Crassous Olivier Pravaz Izabela Bobowska Camille Dagallier (Stanford) Verena Staedele (PSI) Ann Hirt (ETHZ) Urs Gasser (PSI) Stefan Hengsberger(EIF) Frank Scheffold (UniFr) Peter Schurtenberger (ULund)

Funding