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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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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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Examples Molecular level Intra – protein folding Inter – lipid assembly
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Supramolecular Self-assembly Involve more than one molecule Many happens in biological systems. mitochondria virus microvilli
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Top down vs. Bottom Up
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Brownian 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 solid particles dispersed in liquid
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Self-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 assembly concentration 49% volume fraction F=U-TS Hard sphere
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Entropic Interaction F=U-TS Hard sphere Depletion interaction
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Experimental Setup Line-Scanned Optical Tweezers
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Interaction Measurement 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
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Interaction Potential Buffer potential -- optical potential U fd =U optical +U dep
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Compared with the theory
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Assembly by Depletion Interaction Create “Order” Out of “Disorder”--Vrij
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Depletion Interactions between Different Geometry 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
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Making Surface Structures AFM pictures of imprint templates p=0.83 micron
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Colloidal Single Crystals Grown on the Template A confocal image of a colloidal single crystal
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Colloidal Molecules V.N.Manoharan, M.T.Elsesser, D.J.Pine, Science 301, 483 (2003)
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Can we understand molecular assembly and the role of entropy? Colloidal molecules as model systems
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Entropy driven phase separation in 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.
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