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Structure, dynamics and manipulation of colloidal systems in realspace

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Title: Structure, dynamics and manipulation of colloidal systems in realspace


1
Structure, dynamics and manipulation of colloidal
systems in real-space
Roel Dullens
Physical and Theoretical Chemistry
Laboratory Department of Chemistry University of
Oxford
2
Outline
  • Introduction
  • Colloids in real life and as model systems
  • Crystal-Fluid interface of hard spheres
  • Core-shell PMMA colloids
  • 3D single particle imaging
  • Manipulating colloids
  • Optical tweezers deforming 2D colloidal
    crystals
  • Magnetic colloids dipolar fluids and
    explosions

3
What are colloids?
International Union of Pure and Applied Chemistry
The term colloidal refers to a state of
subdivision, implying that the molecules or
polymolecular particles dispersed in a medium
have at least in one direction a dimension
roughly between 1 nm and 1 mm.
4
Colloids in nature milk
5
Colloids in nature blood
6
Colloids in nature clay
1 mm
7
Natural and synthetic colloids latex
8
Colloids as atoms
Same statistical thermo ? Similar phase behaviour
9
Colloids as atoms
The same equations have the same
solutions. Richard Feynman (1918-1988)
…so what is new?
10
Colloidal model systems
3. Colloids are larger and slower than atoms
11
Outline
  • Introduction
  • Colloids in real life and as model systems
  • Crystal-Fluid interface of hard spheres
  • Core-shell PMMA colloids
  • 3D single particle imaging
  • Manipulating colloids
  • Optical tweezers deforming 2D colloidal
    crystals
  • Magnetic colloids dipolar fluids and
    explosions

12
Simplest system hard spheres
Phase diagram
Fluid Crystal
Fluid
Crystal
?
0.494
0.545
Computer Simulations Alder Wainwright (1957),
Wood Jacobson (1957)
13
Experimental hard spheres Colloids Sterically
stabilized PMMA colloids in optically matching
solvent
Glass
Fluid
Crystal
Fluid Crystal
0.494
0.545
?
Pusey and van Megen, Nature, 320, 340 (1986)
14
Crystal-fluid interface
Confocal microscope
RPAD, D.G.A.L. Aarts W.K. Kegel, PRL 97,
228301 (2006)
15
Colloids are seeable and slow
Structure and dynamics at single particle level
16
Crystal-fluid interface
Confocal microscope
RPAD, D.G.A.L. Aarts W.K. Kegel, PRL 97,
228301 (2006)
17
Outline
  • Introduction
  • Colloids in real life and as model systems
  • Crystal-Fluid interface of hard spheres
  • Core-shell PMMA colloids
  • 3D single particle imaging
  • Manipulating colloids
  • Optical tweezers deforming 2D colloidal
    crystals
  • Magnetic colloids dipolar fluids and
    explosions

18
Colloidal materials are soft
Softness of materials ? Youngs modulus E
19
Optical tweezers
20
Optical tweezers
21
Optical tweezers
  • Time-sharing laser-beam
  • Multiple quasi-static traps
  • Control symmetry, density, …

22
Manipulation optical tweezers
  • Dynamic optical tweezing
  • control trap as a function of time

170 x 130 µm2
23
Example micro-mechanics
Optical tweezers microscopic deformation ?
Dragging particles through crystals
170 x 130 µm2
24
Displacement from trap
V 0.25 µm/s
Dissipated energy ? stiffness of crystal
25
Orientational stiffness of 2D crystals
V 0.25 µm/s
  • high symmetry ? low force (energy) ? low
    stiffness
  • low symmetry ? high force (energy) ? high
    stiffness
  • variation in U 100 kBT (!!!)

26
Effect on crystal Strain-field
V 0.25 µm/s
Determination of strain tensor1
ideal
real
Bond-vectors
Lattice spacing ? g(r) Orientation ? angle
distribution
Determine strain tensor e by minimizing
mean-square diff.
1 Falk and Langer, PRE 57, 7192 (1998) Schall
et al., Nature 440, 319 (2006)
27
x-profiles of exx and eyy
V 0.25 µm/s
expansion
compression
28
Angle-dependent strain
V 0.25 µm/s
  • high symmetry ? high strain (exx)
  • low symmetry ? low strain (exx)
  • increasing angle ? increasing strain (eyy)

29
Outline
  • Introduction
  • Colloids in real life and as model systems
  • Crystal-Fluid interface of hard spheres
  • Core-shell PMMA colloids
  • 3D single particle imaging
  • Manipulating colloids
  • Optical tweezers deforming 2D colloidal
    crystals
  • Magnetic colloids dipolar fluids and
    explosions

30
Magneto-rheological fluids
Paramagnetic colloids in external magnetic field
repulsion
B
attraction
B
m0 permeability constant m magnetic moment
Tune interactions using external magnetic field
31
Repulsive quench explosions
B
32
Zigzag-instability in lines
Experiment simulation
Arthur Straube and Ard Louis
33
Rotating fields ...
34
Summary
  • Colloidal systems, confocal microscopy and
    optical tweezers are a very nice
    playground!
  • Structure of hard sphere crystal-fluid interface
  • Orientational stiffness of 2D colloidal
    crystals
  • high symmetry ? low force ? high strain
  • low symmetry ? high force ? low strain
  • Magnetic colloids
  • tunable interaction potential
  • great model system for self-assembly

35
Acknowledgements
Utrecht Volkert de Villeneuve Willem
Kegel Andrei Petukhov Maurice Mourad Maria
Claesson Henk Lekkerkerker Oxford Dirk
Aarts Stuttgart Clemens Bechinger Stefan
Bleil Christopher Hertlein Jens Harting
Rudolf Weeber
36
The end
37
2D colloidal model system
  • small melamine spheres ss 2.9 µm
  • large polystyrene spheres sb 15.5 µm
  • screening of charges (almost) hard sphere
    interactions

Effective size-ratio 4
38
Example micro-mechanics
Dragging a large probe particle through a 2D
crystal
39
Characterization of 2D crystals
snapshot
Voronoi construction
170 x 130 µm2
Np 1890, 170 x 130 µm2
Nearly defect-free 2D crystal
40
Characterization II
radial distribution function
angle distribution
  • sharp well-defined peaks
  • Lattice-spacing 3.5 µm
  • 6 peaks ? single crystal
  • Crystal orientation 18

41
Velocity of probe particle
V 0.25 µm/s
II
I
III
  • Three regimes
  • indentation (I)
  • steady-state (II)
  • relaxation (III)

42
Tuning buoyancy of particles close to and away
from equilibrium
Increasing mass density difference
non-density-matching (non-equilibrium)
density-matching (equilibrium)
43
Visualisation of crystal-fluid interface Particles
that are part of crystalline cluster
Solvent 1
Solvent 2
Solvent 3
  • Crystal nulceation and growth ? increasing
    roughness of interface
  • Dynamic broadening of interface away from
    equilibrium

44
Core-shell PMMA colloids
RPAD et. al., Langmuir 19, 5963 (2003)
Langmuir, 20, 658 (2004)
45
Velocity dependence defect structures
V 0.05 µm/s
V 0.10 µm/s
V 0.25 µm/s
V 0.40 µm/s
V 1.00 µm/s
V 4.00 µm/s
V 8.00 µm/s
V 16.0 µm/s
46
Defect lengths
  • Further work
  • relation defect structure and strain
  • correlation with dissipated energy

47
Displacement vs. strain
V 0.25 µm/s
probe particle
host crystal
48
Number density profile
d3?(z)
z/d
Interfacial width W10-90(d) 8
10-90 width W10-90 Davidchack and Laird, JCP
(108), 9452 9462 (1998)
49
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50
Cornerstones of colloids
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