Self-Assembly of Colloidal ParticlesSelf-Assembly of Colloidal Particles
田安庭 ,孫文瑜 ,林耿慧中央研究院物理所
What is self-assembly?What is self-assembly?
Characteristics-- Spontaneous
-- Increase the organization
-- from Molecule to Galaxy
-- Can be dynamical or static (Equilibrium)
-- Key to nanotechnology
the best way to manufacture things at nano-scale
ExamplesExamples
Molecular level Intra – protein folding Inter – lipid assembly
Supramolecular Self-assemblySupramolecular Self-assembly
Involve more than one moleculeMany happens in biological systems.
mitochondria virus microvilli
Top down vs. Bottom UpTop down vs. Bottom Up
Brownian MotionBrownian Motion
Particles explore accessible phase space by Brownian motion.
Entropy S ~ log is all possible states.
Eg. Spill perfume. Molecules diffuse the whole room.
Colloids: nm – mm solidparticles dispersed in liquid
Self-assembly Colloidal CrystalsSelf-assembly Colloidal Crystals
Iridescence is from the Bragg’s diffraction
What is the role of entropy in self-assemly?
Entropically driven assemblyEntropically driven assembly
concentration
49% volume fraction
F=U-TS
Hard sphere
Entropic InteractionEntropic Interaction
F=U-TSHard sphere
Depletion interaction
Us(h) 2kBTnsR 2(1
h
)2
Experimental SetupExperimental Setup
GalvanometerMirror
Telescope
Nd:YLFLaser
InvertedMicroscope
CCDCamera
=1053 nm
Line-Scanned Optical TweezersLine-Scanned Optical Tweezers
Interaction MeasurementInteraction Measurement
• 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
Interaction PotentialInteraction Potential
Buffer potential -- optical potential
Ufd=Uoptical+Udep
Compared with the theoryCompared with the theory
Assembly by Depletion InteractionAssembly by Depletion Interaction
Create “Order” Out of “Disorder”--Vrij
Depletion Interactions between Depletion Interactions between Different GeometryDifferent Geometry
UB~2UA
UA
A.D. Dinsmore, A.G. Yodh, and D.J. Pine, Nature, 383, 239 (1996), Langmuir 15, 314 (1999).
Geometric Template
Control the positions of colloids by surface topology
Making Surface StructuresMaking Surface 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
AFM pictures of imprint templates
p=0.83 micron
Colloidal Single Crystals Grown on Colloidal Single Crystals Grown on the Templatethe Template
A confocal image of a colloidal single crystal
Colloidal MoleculesColloidal MoleculesV.N.Manoharan, M.T.Elsesser, D.J.Pine, Science 301, 483 (2003)
Can we understand molecular Can we understand molecular assembly and the role of entropy?assembly and the role of entropy?
Colloidal molecules as model systems
Entropy driven phase separation in Entropy driven phase separation in biology?biology?
The DNA is separated from the rest of the cytoplasm in a prokaryote - but there is no nuclear membrane. Can this be an entropic effect due to the depletion attraction?
Goodsell, David S. Our molecular nature : the body's motors, machines and messages, New York : Copernicus, 1996.