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Nano-soft matter

Nano-soft matter. Hsuan-Yi Chen Dept of Physics and Center for Complex Systems, NCU. Outline. Motivation: crazy dreams Self-assembly Non-equilibrium dynamics Summary. Motivation: why is nanoscience important or interesting?. Dream:. Example:.

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Nano-soft matter

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  1. Nano-soft matter Hsuan-Yi Chen Dept of Physics and Center for Complex Systems, NCU

  2. Outline • Motivation: crazy dreams • Self-assembly • Non-equilibrium dynamics • Summary

  3. Motivation: why is nanoscience important or interesting? Dream: Example:

  4. Crazy dreams (good for publicity, and indeed, this is what we want!) We will build nano-machines. Nano-machines will be intellegent and change (save) our lives. How realistic is the above statement?

  5. The true lives in nano-world and the hard facts about our crazy dreams Different dynamics, universal attractive interactions, molecular recognition, mass production, cost/effect……

  6. Back to basic physics of our real world: Intermolecular forces • All from E&M (some are QM) • Direct Coulomb: 1/r • Dipole in external E field 1/r3 • Dipole-dipole • Dipole-induced dipole, van der Waals 1/r6 • Electrolyte, salt, etc. exp(-r/k) • ** A likes A more than A likes B**. Why?? What can these interactions do for us in systems with many (say, 100 to 100,000) particles?

  7. Phase transitions and new phases How to make that kind of structure?? Learn some statistical physics first! Road to equilibrium: F = U-TS  minimum High T: large S, homogeneous phase (ex. Gas) Low T: small U, ordered phase (ex. Crystal) Phase transition: (interaction energy) ~ T  (entropy difference) O.Ikala and G. t. Brinke Science 295 2408 (2002)

  8. F = U – TS A+B A B Phase separation at kT < O(cAB) Simple systems: Binary fluids cAB: energy cost for a pair of A-B neighbors Entropy gain for mixing a pair ofA-B particles ~ kB Want to get cool structures?? Use principles of symmetry breaking. Use polymers.

  9. Symmetry breaking : road to special “patterns” Solidification: isotropic fluid phase  anisotropic solid Rev. Mod. Phys. 52, 1 (1980) Large curvature = large temperature gradient = fast growth

  10. Polymers: material to make “patterns” homopolymer coarse-grained view take thermal fluctuations into account Size: submicron

  11. Block copolymers: designer’s material A B + AB diblock copolymer A C B ABC (linear) triblock copolymer + + + + ABC triblock star + + + + comb

  12. Modeling diblock copolymers c Interaction between A, B links. AB f Volume fraction of A links. A N Number of links along a chain. More parameters will be used if we consider more complicated architectures.

  13. What do we expect to get from diblock copolymer melt? Physics Today, Feb. 1999, p32.

  14. Principles of pattern selection in block copolymer melt • F = F(elastic) + F(interfacial) • F(elastic) ~ (domain size)2 • F(interfacial) ~ (domain size)-1 • F(homogeneous) ~ c fAfBN • Compare free energy per chain for different phases.

  15. Phases of diblock copolymer

  16. Self-assembly occurs in other systems, too.

  17. What we will see when there are three? Physics Today, Feb. 1999, p32

  18. Applications: dots M. Park, C. Harrison, P.M. Chaikin, R.A. Register, and D.H. Adamson Science 276, 1401 (1997)

  19. Application: Wires Thurn-Albrecht, J. Schotter, et al., Science 290, 2126 (2000)

  20. Making patterned surface S.O. Kim, et. al., Nature 424, (2003)

  21. Polymer “alloys” designed in nanoscale C.Y. Ryu, et al, Macromolecules, 35 9391 (2002) triblock pentablock

  22. Nano-particles on droplets

  23. Nonequilibrium dynamics: make nano-machines • Nonequilibrium: beyond “partition function” physics. • What is new for motion in “wet” environment, at nm scale? • Can we utilize these special features?

  24. Navier-Stokes equation and Reynolds number in nm scale inertia effect viscous effect In cgs units:l~10-7, v~10-7, h~1, r~1 Re<<1. Strongly overdamped motion.

  25. protein folding and protein motors: overdamped, Brownian motion Science 1999 Nov 26; 286: 1687. Robert H. Fillingame http://folding.stanford.edu/education/prstruc.html

  26. Microtubule: non-equilibrium, self-assembled tracks in cells I.M. Janosi et al, Eur. Biophys. J. 27, 501 (1998)

  27. Filaments in a cell http://www.accessexcellence.org/AB/GG/cytoSkeleton.html

  28. 10 nm +2 + - + - + - + Nano-machines work on the tracks Rev. Mod. Phys. 69, 1269 (1997) Brownian motion is important for life.

  29. Application:Particle separation by Brownian motors R.D. Astumian, Science, 276, 917 (1997)

  30. Road to artificial motor Nature 401(1999)

  31. How are we doing with the artificial motor? Not very good, not too bad, either.

  32. Nanodevice with natural rotatory motors Science 290, (2002)

  33. A rotatory motor at work

  34. How to make structures like this? (inside a cell) Need to construct simpler model systems to understand pattern formation in systems of this kind.

  35. Leibler 97: quasi-2d experiments Kinesin “multimers”. Kinesins move towards “+” ends. Finally they accumulate near the center. Taxol: control microtubule length and number Most of the exp were done without taxol.

  36. Leibler 97: aster and vortex 1. Microtubule length: short = aster, long = vortex. 2. Get vortex at late time due to a “buckling instability”. 3. Forming aster is not the only possible route leading to the vortex structure.

  37. Leibler 97: large systems • Kinesin concentration has important effects on the resulting pattern. (low=vortices, medium=asters, high=bundles) • When two asters overlap sufficiently, they can merge. This process may determine final distance between asters.

  38. Leibler 01: One motor result (still 2d) + end points outward for Ncd + MT (see MT seed in `h’) Kinesin: + end motor Ncd: - end motor Vortices only seen in kinesin exp

  39. Leibler 01: Two motors result Motor concentration increases  Local MT bundles, poles between bundles Low kinesin/Ncdstars High kinesin/Ncd vortices Kinesin localized in every other pole (+ poles)

  40. Summary • Why “nano”?? Why “soft nano”?? • Successful story: self-assembled nanostructures. • Failure: real, nano, artificial machines. • One thing for sure: go study physics hard.

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