Ellipsoidal Hybrid Magnetic Microgel Particles with Thermally Tunable Aspect Ratios

Transcription

1 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 F herve.dietsch@unifr.ch

2 Functionalized Building Blocks: Colloids, Polymers, Surfactants Particles 2011 conference Interactions, Phase Behavior, Microstructure Structures and Particle Assemblies Particle-particle interactions Particle-solvent interactions Eventually as a function of the used stimulus Building Blocks Soft Materials Crystallization, Phase Separation, Gelation Stimuli-Responsive Particles Properties Temperature, Magnetic field, Light, ph, Molecule to be detected, Protein Nanostructured Materials -> Novel Properties: I 12. July 2011 I p. 2

3 Thermoresponsive particles: LCST and VPTT Microscopic scale Example: PNIPAM a thermosensitive polymer Linear chain microgel (network) Microgel behavior good solvent => swollen T c 33ºC poor solvent => collapsed soft shell hard sphere T<LCST T>LCST LCST PNIPAM ~33 C Low Critical Solution Temperature VPTT Volume Phase Transition Temperature I 12. July 2011 I p. 3 H 2 H 2

4 Thermoresponsive particles: LCST and VPTT Microscopic scale Example: PNIPAM a thermosensitive polymer Size, volume fraction Linear chain microgel (network) and Microgel behavior good solvent => swollen T c 33ºC poor solvent => collapsed Interactions control soft shell hard sphere ne single trigger: Temperature T<LCST T>LCST H 2 H 2 LCST PNIPAM ~33 C Low Critical Solution Temperature VPTT Volume Phase Transition Temperature I 12. July 2011 I p. 4

5 Another Stimulus and morphology: Ellipsoidal-shaped Magnetic Particles a Submicrosized 80nm<a<150nm Without phosphate ions 3 6 Isotropic particle Matijevic et. al caña et. al I 12. July 2011 I p. 5

6 Alternative: Tuning the aspect ratio by silica coating TES in H 2 in Ethanol NH 3 I 12. July 2011 I p. 6 Based on Graf et. al. 2003

7 Alternative: Tuning the aspect ratio by silica coating TES in H 2 in Ethanol NH 3 I 12. July 2011 I p. 7 Based on Graf et. al. 2003

8 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, More I 12. July about 2011 magnetic I p. 8 properties: M. Reufer, HD et al., J Phys. Cond. Matter, 2011, 23,

9 Control of the surface chemistry thanks to the silica layer R' R' H H H H H H H H silane agent R' R R Si R' R' S i S i S i S i S i S i S i S i R' R' R' R R' + H-R H 3 C CH 2 H 3 C Si CH 3 CH 3 silane agent I 12. July 2011 I p. 9 Surface modification

10 Hybrid combination with the thermoresponsive PNIPAM shell Monomer, cross-linker, initiator, Δ Reactive silane on the surface Precipitation polymerization H 2 C HN CH 3 H 3 C NIPAM I 12. July 2011 I p. 10 α-fe 2 3 /PNIPAM C. Dagallier, H. Dietsch*, P. Schurtenberger and F. Scheffold, Soft Matter, 2010, 6(10):

11 Temperature response and dynamical arrest R h [nm] DLS R b2 R b1 R h 0.03M NaSCN R h T [ C] R a Hydrodynamic radius of hematite-pnipam PNiPAM microgel core-shell vs. particles temperature. vs. temperature. V V T Φ 15 C R b1 R b1 >R b2 >R a 30 C R b2 I 12. July 2011 I p. 11

12 Direction of Light beam Probing the rotation of hybrid microgels Pre-alignment 35 C Setup (Microscope) B B 35 C 10 C B 10 C birefringent Experiment: temperature ramp P CCD P A H A I 12. July 2011 I p. 12

13 Direction of Light beam Probing the rotation of hybrid microgels Pre-alignment 35 C Setup (Microscope) B B 35 C 10 C B 10 C birefringent Experiment: temperature ramp P CCD P A H A I 12. July 2011 I p. 13

14 Properties of the hybrid microgels PNIPAM microgels Hematite particles C. Dagallier, H. Dietsch*, P. Schurtenberger and F. Scheffold, Soft Matter, 2010, 6(10): I 12. July 2011 I p. 14

15 Properties of the hybrid microgels PNIPAM microgels ptical anisotropy, magnetic orientation control Hematite particles Size, volume fraction, Interactions control, Two triggers: Temperature and Magnetic field C. Dagallier, H. Dietsch*, P. Schurtenberger and F. Scheffold, Soft Matter, 2010, 6(10): I 12. July 2011 I p. 15

16 Remaining challenges Increase the magnetic response Hematite are canted-antiferromagnetic rientation under magnetic field along the long axis Morphology changes with temperature y x H y z H T I 12. July 2011 I p. 16

17 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

18 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 livier Pravaz Jérôme Crassous I 12. July 2011 I p. 18