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

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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