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..