12. July 2011 Ellipsoidal Hybrid Magnetic Microgel Particles with Thermally Tunable Aspect Ratios Hervé Dietsch, Particles 2011 Conference 9-12 July 2011 Université de Fribourg T +41 26 300 91 37 herve.dietsch@unifr.ch Adolphe Merkle Institute Rte de l‘Ancienne Papeterie 3 F +41 26 300 97 47 www.am-institute.ch CH-1723 Marly
Functionalized Building Blocks: Colloids, Polymers, Surfactants Building Particles 2011 conference Blocks Interactions, Phase Behavior, Stimuli-Responsive Particles Microstructure Temperature, Soft Magnetic field, Materials Light, pH, Structures Properties Molecule to be detected, Protein… Nanostructured Materials and Particle Assemblies Crystallization, -> Novel Properties: Particle-particle interactions Phase Particle-solvent interactions Separation, Gelation Eventually as a function of the used stimulus I 12. July 2011 I p. 2
Thermoresponsive particles: LCST and VPTT Microscopic scale Example: PNIPAM a thermosensitive polymer Microgel behavior microgel Linear chain T c ≈ 33 ºC T c ≈ 33 ºC good solvent good solvent poor solvent poor solvent (network) => swollen => swollen => collapsed => collapsed hard sphere hard sphere soft shell soft shell T<LCST T>LCST H 2 O H 2 O H 2 O H 2 O H 2 O H 2 O LCST PNIPAM ~33°C Low Critical Solution Temperature VPTT Volume Phase Transition Temperature I 12. July 2011 I p. 3
Thermoresponsive particles: LCST and VPTT Microscopic scale Example: PNIPAM a thermosensitive polymer Size, volume fraction Microgel behavior microgel Linear chain T c ≈ 33 ºC T c ≈ 33 ºC and good solvent good solvent poor solvent poor solvent (network) => swollen => swollen => collapsed => collapsed Interactions control hard sphere hard sphere soft shell soft shell One single trigger: Temperature T<LCST T>LCST H 2 O H 2 O H 2 O H 2 O H 2 O H 2 O LCST PNIPAM ~33°C Low Critical Solution Temperature VPTT Volume Phase Transition Temperature I 12. July 2011 I p. 4
a Another Stimulus and morphology: Ellipsoidal-shaped Magnetic Particles Submicrosized 80nm<a<150nm 3 Without 6 phosphate ions Isotropic particle Matijevic et. al. 1978 Ocaña et. al. 1999 I 12. July 2011 I p. 5
Alternative: Tuning the aspect ratio by silica coating TEOS in H 2 O in Ethanol NH 3 I 12. July 2011 I p. 6 Based on Graf et. al. 2003
Alternative: Tuning the aspect ratio by silica coating TEOS in H 2 O in Ethanol NH 3 I 12. July 2011 I p. 7 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 I p. 8 More about magnetic 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 O R' S i silane agent OH S i S i O HO OH O O O O R' S i O O S i HO OH R' R' O O O O O HO OH R S i S i OH S i R' O R Si O R' R + H-R R' O H 3 C O CH 2 H 3 C Si O O O CH 3 CH 3 silane agent Surface modification I 12. July 2011 I p. 9
Hybrid combination with the thermoresponsive PNIPAM shell Monomer, cross-linker, initiator, Δ Precipitation Reactive silane on polymerization the surface H 2 C O H N CH 3 H 3 C NIPAM α -Fe 2 O 3 /PNIPAM C. Dagallier, H. Dietsch*, P. Schurtenberger and F. Scheffold, Soft Matter, 2010, 6(10): 2174-2177 I 12. July 2011 I p. 10
Temperature response and dynamical arrest DLS DLS 550 R b2 R b2 120 500 R b1 R b1 450 100 R [nm] R h [nm] 400 V 80 350 R a R h 0.03M NaSCN R a 15°C R b1 300 T 60 R h 250 40 Φ 200 15 20 25 30 35 40 15 20 25 30 35 40 45 T [°C] T [°C] Hydrodynamic radius of hematite-PNIPAM Hydrodynamic radius of PNiPAM microgel core-shell particles vs. temperature. vs. temperature. V R b1 >R b2 >R a 30°C R b2 I 12. July 2011 I p. 11
Probing the rotation of hybrid microgels Pre-alignment Setup (Microscope) Direction of Light beam 35°C 35°C B B 10°C B 10°C birefringent CCD P P Experiment: temperature ramp A A H I 12. July 2011 I p. 12
Probing the rotation of hybrid microgels Pre-alignment Setup (Microscope) Direction of Light beam 35°C 35°C B B 10°C B 10°C birefringent CCD P P Experiment: temperature ramp A A H I 12. July 2011 I p. 13
Properties of the hybrid microgels PNIPAM microgels Hematite particles C. Dagallier, H. Dietsch*, P. Schurtenberger and F. Scheffold, Soft Matter, 2010, 6(10): 2174-2177 I 12. July 2011 I p. 14
Properties of the hybrid microgels Size, volume fraction, Interactions control, Optical anisotropy, magnetic orientation control PNIPAM microgels Two triggers: Temperature and Magnetic field Hematite particles C. Dagallier, H. Dietsch*, P. Schurtenberger and F. Scheffold, Soft Matter, 2010, 6(10): 2174-2177 I 12. July 2011 I p. 15
Remaining challenges • Increase the magnetic response Hematite are canted-antiferromagnetic • Orientation under magnetic field along the long axis y y H H x z • Morphology changes with temperature T I 12. July 2011 I p. 16
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. 17
The Group Camille Dagallier (Stanford) Liliane Ackermann Adriana Mihut Shuo Bai Verena Staedele (PSI) Ann Hirt (ETHZ) Urs Gasser (PSI) Stefan Hengsberger(EIF) Frank Scheffold (UniFr) Peter Schurtenberger (ULund) Funding Izabela Bobowska Olivier Pravaz Jérôme Crassous I 12. July 2011 I p. 18
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