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Presented by
Ashis MukhopadhyayWayne State University
Soft MatterResearch challenges and opportunities
Everyday examples
Definition
Research areas
Everyday examples
Think yourself at the airport screening
Pierre-Gilles de Gennes:
“All physiochemical systems that have large response functions.”
Example: Rubber of the Amazon Indians (Nobel Lecture, 1991)
Liquid
Rubber
What is soft matter?
Dramatic change of mechanical properties from a mild chemical reaction
Richard A. L. Jones, in Soft Condensed Matter:
“Materials in states of matter that are neither simple
liquids nor crystalline solids..;”
Radial distribution function
Helmut Möhwald:
“Materials that are held together by non-covalent interactions.”
euro-cosmetics.com
Shear-thinning
• These are examples of non-Newtonian fluids
Let’s watch Sheldon Cooper of Big Bang theory
https://www.youtube.com/watch?v=2CJJ6FrfuGU&t=45s
https://sites.google.com/view/mccready-williams-research/home
Interactions• H-bonding
• Screened Coulomb
• van der Waals
• Hydrophobic
• depletion
• capillary
Associated energy kBT 0.03 eV 4 pN nm
Building blocks: Colloids, liquid crystals, surfactants, polymers, proteins, etc.
Structural phase transitions, glass transitions, pattern formation,
self-assembly, etc.
Log (length scale) nm
Amphiphile Bilayer Unilamellar vesicle Layered stacks Multilamellar vesicle
1 10 100 1000
Questions we are trying to answer:
Polymers: How nanoparticle move through a polymer network
Colloids: What is the nature of crystals and defects on a curved surface?
C CH
H
H
R
C CH
H
H
RN
N ~ 102 - 105
Degree of
Polymerization,
Polymers
Molecular weight: 103 g/mol to 107 g/mol
Polymer architecture
linearring star
H-branched
comb
ladderdendrimer
Heteropolymers
…A-B-A-B-A-B-A-B-A-B-A-B… …A-A-B-A-B-B-A-B-B-A-A-B-B-B…
…A-A-A-A-A-A-B-B-B-B-B-B-B…
alternating random
block
As surfactants
Micro-phase separation
Everyday examples: plastic cup, bottle, toy, tire, pillow, sofa, shirt, shoe,
bulletproof vest, newspaper, book, photograph, pen, eyeglass lens,
toothbrush, diaper, paint, CD or DVD, flexible circuit board, etc.
Medical examples: medical instruments to materials for endoscopic,
catheterization, and angioplastic procedures, to infection-control barriers,
intravenous tubes, dressings, and sutures, to pills, drug-delivery vehicles,
transdermal patches, and targeted antitumor agents, to implants anywhere
in the body, tissue engineering, intraocular lenses, dental restorative
materials, etc.
The universe of polymers
Molecular dynamics of polymer chain
Length scale: 0.1 nm - 100 nm
Time scale: 10-12 s - few milliseconds
A smarter choice
Polymer dynamics
Brownian motion of a particle in the matrix
Manifestation of statistical fluctuation
Brownian motion of 1 µm particles in water
r2= 6Dt D=Diffusion coefficient
How the friction coefficient depends upon the length scale & time scale
in polymers and in other complex fluids?
Einstein’s fluctuation-dissipation theorem: D= kBT/
= friction coefficient
Important caveat: Many orders of magnitude difference in time scales
Some results
1 10
1
10
100
1000
DGLE
+DhopD
GLE
D/D
SE
2Ro/d
t
0.10.1 0.2 0.3 0.4
0.01
0.1
1
10
-4.07
-2.28
-1.45
2.5 nm, 5k
2.5 nm, 35k
5 nm, 35k
10 nm, 35k
Power Law Fit
Hydrodynamic Fit
D (
m
2/s
)
Power law scaling
instead of exponential
• Hydrodynamics
• Obstruction & depletion effects
• Segmental motion
• Entanglement dynamics
• Caging & hopping
• Anomalous subdiffusion
Einstein theory
Generalized Langevin theory
More recent theories and simulations
Advanced scaling theory
Rubinstein et. al.
Importance of hopping motion
Schweizer et. al.
Statistical dynamical theory
Prediction of D/DSE vs. 2R0/a
MD simulation by Kumar, Grest, Schweizer
MD simulation near a nanoscale notch
Balazs, et. al Science (2006)
Polymer with spherical nanoparticles
Self-healing Polymer NanocompositesResearch project:
Role of depletion interaction?
Research project: Effects of crowding in biology and soft matter
A day in Calcutta, India
Effect of obstruction
Examples of Crowding in biology
Interior of a cell
Molecular motor
Nanoparticle dynamics through mucus
Not something to talk about at
the dinner table!
Diseases: Asthma, bronchitis, cystic fibrosis, inflammatory bowel disease
An important biomaterial: shield against pathogens, maintain wet environment,
exchange gas, nutrients, etc.
Mucin molecule, a glycoprotein
Nanoparticle dynamics through mucus
SEM image
b
dt 2Ro Lp
Rg
An entangled network /
viscous biogel
• Heterogeneity
• Adhesivity
• “Stealth” particles
• Particle of anisotropic shape
• Role of microscopic friction
• Active and passive transport in other
crowded system.
Gold nanoparticles of variable sizes for nano-dynamics
Nature 2013
Ultrafast laser spectroscopy
• An ensemble of very few molecules
• A large number fluctuations about a thermodynamic average
Thermal fluctuation~ kBT
V ~ 1 fL
<N> ~ 1
Objective
Pulsed Laser
Statistical physics of the system:
Fluctuations caught in the act
Reconfigurable Colloidal Assembly
Research Project:
Colloidal interaction and self-assembly by temperature
Gecko feet
Spider silk
Our Lego blocks: Colloidal discs and ellipsoids
Elongational strain
Uniaxial compression
We can make helices and rings using colloidal discs
Larger ones settle at the bottom
2 m
10 m
Colloidal Rings
We can make colloidal domes
‘z’ scan of one dome
Confocal microscopy image
Side view
Packing of marbles on a flat surface
Spherical Crystallography
How particles pack on a curved surface
Soccer ball
20 hexagons + 12 pentagons
Mathematician L. Euler
Topological charge
Pentagons= +1
Heptagons= -1
5-7 defects in carbon nanotubes
5 m
5-7 defects in colloidal domes Fourier transform
Also C60
5 m
5 m
25 µm (a) (c)
(b) (d)
5 m
5-7 defects in colloidal domes
Delaunay triangulation
Melting
Voronoi construction and Delaunay triangulation
Melting
Bond orientational order parameter
𝑔6 𝑟 = < 𝜓6∗ 0 𝜓6( Ԧ𝑟) >
𝜓6 𝑟𝑖 =1
𝑛
𝑗=1
𝑛
exp [𝑖6Ѳ 𝑟𝑖𝑗 ]
0 2 4 6 8 100
3
6
9
12
15
g(r
)
r (m)
Radial distribution function during melting
Particle dynamics during melting
1 10
0.01
0.1
1
(s
)
q (m-1)
-2
Liquid phase
Crystalline phase
Soft matter
-polymers, biopolymers, colloids, hybrid materials,
self-assembled structures
The scope is larger than physics
-with some fluid physics, chemistry, statistical mechanics,
image processing, computer simulation, etc.
Experimental methods: Ultrafast laser spectroscopy,
confocal microscopy, ellipsometry, Langmuir-Blodgett techniques,
AFM, image & large data analysis, surface chemistry, nano particle
synthesis, functionalization, and characterization, etc.
Concluding remarks:
Future job market: academia, industry, medical schools,
national labs, etc..