1. Self-Assembly of Colloidal Systems and Its Application Keng-hui Lin 林耿慧 Institute of Physics Academia Sinica

2. Outline  Overview of Soft Condensed Matter Physics  Colloidal Systems  Entropy Driven Phenomena  Packing in Confined Space  Application in Tissue Engineering

3. Overview of Soft Condensed Matter Definition: Physics of the system with the energy scale of k B T. The systems of interests include colloids, polymers, liquid crystals, emulsions, membranes, proteins, cells, etc.. Self-Assembly

4. Examples of Colloidal Systems Examples – paint, proteins, ink, nanoparticles, e-paper etc. Narrow Definition: Solid particles dispersed in liquid Broad Definition: Two immiscible phases uniformly dispersed to each other

5. Scientific Importance – Jean Perrin, 1911 Nobel Laureate, the first hard sphere system, model system Interparticle Interactions – electrostatic, van der Waal Interaction, hydrodynamic, entropic…etc. Shapes – spheres, rod, blobs... 2a - - - - - - - - Physical Properties of Colloidal Systems Phase behavior: F=U-TS

6. Self-Assembly of Collodial Crystals Optimal packing to maximize entropy Is fcc/hexagonal closed pack volume fraction

7. Depletion Interactions

8. 180 Hz Line-Scanned Optical Tweezers

9. Find the centroids of colloids Measure the separation of two beads 30 minutes video tape -> 10 5 measurements The probability of separation Spatial resolution ~ 30 nm, Energy resolution ~0.05 k B T Video Microscopy

10. buffer fd Buffer potential -- optical potential U fd =U optical +U dep Differential Measurement

11. 1.0  m particles YJM model L=0.88  m fd Depletion Interactions

12. A.D. Dinsmore, A.G. Yodh, and D.J. Pine, Nature, 383, 239 (1996), Langmuir 15, 314 (1999). Control the positions of colloids by surface topology Depletion Interactions with Structures

13. J. Vac. Soc. Tech. B. 15, 2897 (1997), Steve Chou et al. AFM pictures of imprint templates p=0.46 micron p=0.83 micron thermal imprint Imprint with Gratings

14. 2D Structures on Line Gratings

15. 2D structures on Crossed Gratings

16. FCC Crystals Confocal picture of FCC crystals

17. Colloids Entrapped In Emulsions V.N. Manoharan, M.T.Elsesser, D.J. Pine Science 301 483 (2003)

18. Colloids in Small Confines with Depletion Interactions Different packing from the one without depletion interactions

19. Paradigm of Tissue Engineering Scaffold Scaffold Drug, nutrition, … Cells

20. Making of Bubbles with Flow-focusing Microfluidic Device

21. Making of 3D ordered porous foam

22. Cell Encapsulation

23. Conclusions  Advanced optical microscopy  The role of entropy  Assembly of different micro- structures  The interplay between cells and the microstructure environment

24. Group