Nano-soft matter Hsuan-Yi Chen Dept of Physics and Center for Complex Systems, NCU.
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Transcript of Nano-soft matter Hsuan-Yi Chen Dept of Physics and Center for Complex Systems, NCU.
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Nano-soft matter
Hsuan-Yi ChenDept of Physics and Center for Complex Systems, NC
U
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Outline
• Motivation: crazy dreams • Self-assembly• Non-equilibrium dynamics• Summary
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Motivation: why is nanoscience important or interesting?
Dream: Example:
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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?
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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……
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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 withmany (say, 100 to 100,000) particles?
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Phase transitions and new phases
How to make that kind of structure??
Learn some statistical physics first!
Road to equilibrium: F = U-TS minimumHigh 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. BrinkeScience 295 2408 (2002)
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AB: energy cost for a pair of A-B neighbors Entropy gain for mixing a pair ofA-B particles ~ kB
Simple systems: Binary fluids
A
B
F = U – TS
Phase separation at kT < O(AB)
A+B
Want to get cool structures?? Use principles of symmetry breaking.Use polymers.
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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
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Polymers: material to make “patterns”
homopolymer
coarse-grained view
take thermal fluctuationsinto accountSize: submicron
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+
++
+ +
+ + + +
AB diblock copolymer
ABC (linear) triblock copolymer
ABC triblock star
comb
A B
A B C
Block copolymers: designer’s material
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AB Interaction between A, B links.
f A Volume fraction of A links.
N Number of links along a chain.
More parameters will be used if we consider more complicated architectures.
Modeling diblock copolymers
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Physics Today, Feb. 1999, p32.
What do we expect to get from diblock copolymer melt?
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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) ~ fAfBN• Compare free energy per chain for diff
erent phases.
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Phases of diblock copolymer
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Self-assembly occurs in other systems, too.
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Physics Today, Feb. 1999, p32
What we will see when there are three?
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Applications: dots
M. Park, C. Harrison, P.M. Chaikin, R.A. Register, and D.H. Adamson
Science 276, 1401 (1997)
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Application: Wires
Thurn-Albrecht, J. Schotter, et al.,
Science 290, 2126 (2000)
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S.O. Kim, et. al., Nature 424, (2003)
Making patterned surface
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Polymer “alloys” designed in nanoscale
triblock pentablock
C.Y. Ryu, et al, Macromolecules, 35 9391 (2002)
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Nano-particles on droplets
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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?
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Navier-Stokes equation and Reynolds number in nm scale
In cgs units: l~10-7, v~10-7, Re<<1. Strongly overdamped motion.
inertia effect viscous effect
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protein folding and protein motors: overdamped, Brownian motion
http://folding.stanford.edu/education/prstruc.html
Science 1999 Nov 26; 286: 1687.
Robert H. Fillingame
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I.M. Janosi et al, Eur. Biophys. J. 27, 501 (1998)
Microtubule: non-equilibrium, self-assembled tracks in cells
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Filaments in a cell
http://www.accessexcellence.org/AB/GG/cytoSkeleton.html
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+ - + - + - +
+2 10 nmRev. Mod. Phys. 69, 1269 (1997)
Nano-machines work on the tracks
Brownian motion is important for life.
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R.D. Astumian, Science, 276, 917 (1997)
Application:Particle separation by Brownian motors
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Nature 401(1999)
Road to artificial motor
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Not very good, not too bad, either.
How are we doing with the artificial motor?
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Science 290, (2002)
Nanodevice with natural rotatory motors
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A rotatory motor at work
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How to make structures like this? (inside a cell)
Need to construct simpler model systems to understand pattern formation in systems of this kind.
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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.
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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.
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Leibler 97: large systems
1. Kinesin concentration has important effects on the resulting pattern. (low=vortices, medium=asters, high=bundles)
2. When two asters overlap sufficiently, they can merge. This process may determine final distance between asters.
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Leibler 01: One motor result (still 2d)
Kinesin: + end motorNcd: - end motorVortices only seen in kinesin exp
+ end points outward for Ncd + MT (see MT seed in `h’)
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Leibler 01: Two motors result
Motor concentration increases Local MT bundles, poles between bundles
Low kinesin/NcdstarsHigh kinesin/Ncd vortices
Kinesin localized in every other pole(+ poles)
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Summary
• Why “nano”?? Why “soft nano”??• Successful story: self-assembled nano
structures.• Failure: real, nano, artificial machines.• One thing for sure: go study physics h
ard.