self-assembly of colloidal particles 田安庭, 孫文瑜, 林耿慧 中央研究院物理所
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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
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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
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ExamplesExamples
Molecular level Intra – protein folding Inter – lipid assembly
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Supramolecular Self-assemblySupramolecular Self-assembly
Involve more than one moleculeMany happens in biological systems.
mitochondria virus microvilli
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Top down vs. Bottom UpTop down vs. Bottom Up
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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
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Self-assembly Colloidal CrystalsSelf-assembly Colloidal Crystals
Iridescence is from the Bragg’s diffraction
What is the role of entropy in self-assemly?
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Entropically driven assemblyEntropically driven assembly
concentration
49% volume fraction
F=U-TS
Hard sphere
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Entropic InteractionEntropic Interaction
F=U-TSHard sphere
Depletion interaction
Us(h) 2kBTnsR 2(1
h
)2
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Experimental SetupExperimental Setup
GalvanometerMirror
Telescope
Nd:YLFLaser
InvertedMicroscope
CCDCamera
=1053 nm
Line-Scanned Optical TweezersLine-Scanned Optical Tweezers
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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
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Interaction PotentialInteraction Potential
Buffer potential -- optical potential
Ufd=Uoptical+Udep
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Compared with the theoryCompared with the theory
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Assembly by Depletion InteractionAssembly by Depletion Interaction
Create “Order” Out of “Disorder”--Vrij
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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
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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
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Colloidal Single Crystals Grown on Colloidal Single Crystals Grown on the Templatethe Template
A confocal image of a colloidal single crystal
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Colloidal MoleculesColloidal MoleculesV.N.Manoharan, M.T.Elsesser, D.J.Pine, Science 301, 483 (2003)
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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
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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.