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Self-Assembly of Colloidal Self-Assembly of Colloidal Systems and Its Application Systems and Its Application
Keng-hui Lin 林耿慧Institute of PhysicsAcademia Sinica
Outline
Overview of Soft Condensed Matter Physics
Colloidal Systems Entropy Driven Phenomena Packing in Confined Space Application in Tissue Engineering
Overview of Soft Condensed Matter
Definition: Physics of the system with the energy scale of kBT.The systems of interests include colloids, polymers, liquid crystals, emulsions, membranes, proteins, cells, etc..
Self-Assembly
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
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
Self-Assembly of Collodial Crystals
Optimal packing to maximize entropy Is fcc/hexagonal closed pack
volume fraction
Depletion Interactions
L
2a
GalvanometerMirror
Telescope
Nd:YLFLaser
InvertedMicroscope
CCDCamera
=1053 nm
180 Hz
Line-Scanned Optical Tweezers
• Find the centroids of colloids• Measure the separation of two beads• 30 minutes video tape -> 105 measurements• The probability of separation
P(r)exp( U(r)kBT
)
• Spatial resolution ~ 30 nm, • Energy resolution ~0.05 kBT
Video Microscopy
bufferfd
Buffer potential -- optical potential
Ufd=Uoptical+Udep
Differential Measurement
1.0 m particles
U(h;a / L) kBTnraL2K(h / L;a /L) YJM model L=0.88 m
fd Depletion Interactions
A.D. Dinsmore, A.G. Yodh, and D.J. Pine, Nature, 383, 239 (1996), Langmuir 15, 314 (1999).
UB~2UA
UA
Geometric Template
Control the positions of colloids by surface topology
Depletion Interactions with Structures
glass substrate PMMA layer
grating
(>200 nm thick)
Press a grating onto PMMA layer whileheating PMMA above its glass temperature.
aCommercially availablegrating pitches rangefrom 0.3 micron to 10 micron.
Remove the grating afterPMMA is cool.
b
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
2D Structures on Line Gratings
2a
p
=
d
d/p
2D structures on Crossed Gratings
2a
p =
d
d/p
average particle spacing
FCC Crystals
Confocal picture of FCC crystals
Colloids Entrapped In EmulsionsV.N. Manoharan, M.T.Elsesser, D.J. Pine Science 301 483 (2003)
Colloids in Small Confines with Depletion Interactions
Different packing from the one without depletion interactions
Paradigm of Tissue Engineering Scaffold
Scaffold Drug, nutrition, …
Cells
Making of Bubbles with Flow-focusing Microfluidic Device
Making of 3D ordered porous foam
Cell Encapsulation
Conclusions
Advanced optical microscopy The role of entropy Assembly of different micro-
structures The interplay between cells and the
microstructure environment
Group