Download A. Sokolov: Dynamics in Soft Materials

Group of Dr. Sokolov
November 2009
Dynamics in Soft Materials
UT
ORNL
Soft Matter
Polymers
Glass-forming
Systems
Colloids
Foams and Gels
Biological Systems
November 2009
Liquid Crystals
November 2009
Characteristics of Soft Materials:
Variety of states and large degrees of freedom, metastable states;
Delicate balance between Entropic and Enthalpic contributions to the Free
Energy;
Large thermal fluctuations and high sensitivity to external conditions;
Macroscopic softness.
Soft Matter Physics:
Extremely high complexity of the systems and of the physical phenomena
Traditional approximations often fail
Mostly phenomenological level, qualitative considerations
Many assumptions, some of them are not justified
Dynamics is the Key to many Macroscopic Properties
of Soft Materials
Main directions of research in our group
•
log or logn+A
Polymer Dynamics, Glass Transition
2
November 2009
Dynamics and Function of Biopolymers
Chain relaxation
0
POB,PPG,PIP,aPP,PS,PC
PPG
-2
PIP
-4
aPP
POB
-6
PS
0.85
0.90
PC
Segmental
relaxation
Tg/T
0.95
Nanostructured and Nanocomposite
Materials
1.00
DNA
Protein Lysozyme
RNA
Nano-Photonics, Plasmonics
Main Experimental Techniques
November 2009
Light scattering: Raman and Brillouin scattering
spectroscopy, plus dynamic light scattering cover the
frequency range from mHz up to ~100 THz (corresponding
time scales from hours to femtoseconds ).
Dielectric relaxation spectroscopy covers frequency range
from mHz up to ~50 GHz.
Neutron scattering: use of SNS facilities at ORNL, NIST
facilities, and also facilities in Europe. Although frequency
range in that case is more limited (from MHz to ~100
THz), neutron scattering provides detailed microscopic
information.
Optical microscopy combined with spectroscopy (Raman, fluorescence, etc.):
- confocal with lateral resolution ~0.5 mm;
- apertureless near-field microscopy with ~20 nm lateral resolution.
November 2009
Collaborations
USA
NIST
Polymer Division
Center for Neutron Research
AFRL
NRL
ORNL
Johns Hopkins University
University of Maryland
Kent State University
Bridgestone/Firestone
Lubrizol
International
IA&E Russ.Ac.Sciences
Bayreuth University
Research Center Juelich
University Paris Sud
ILL & ESRF, Grenoble
Chalmers Univ.of Technology
Universita di Messina
Universita ‘La Sapienza’
University of Oxford
Horiba JY
Silesian University
Russia
Germany
Germany
France
France
Sweden
Italy
Italy
UK
France
Poland
Main Philosophy in our Group
November 2009
After one year in my group I expect from a graduate student:
Independence in your research, I’m just an advisor
Even “wrong” ideas are better than no ideas at all
You propose what should we do (not me telling you what to do)
Team work
Presentation of results is very important part of your work; every student gives
presentations a few times per year on the group meetings; good students attend
national and international meetings
You are writing papers, I’m just helping and teaching you how to write and
how to deal with referees
Polymer Dynamics, Glass Transition
November 2009
The main goal is fundamental understanding of molecular motion and its
relationship to macroscopic properties of polymeric and other glass forming
materials.
We study, among other questions:
-Glass transition; Cooperativity in molecular motions; Role of dynamic
heterogeneities
As an example:
Our recent finding – universality of
chain relaxation behavior for many
polymers when presented vs Tg/T
[PRL 102, 248301(2009); Macromolecules
39, 3322 (2006)].
Back
log or logn+A
-Temperature variations of viscoelastic
Decoupling phenomena in dynamics …
and
2
mechanical
properties,
Chain relaxation
0
POB,PPG,PIP,aPP,PS,PC
PPG
-2
PIP
-4
PC
aPP
POB
-6
PS
0.85
0.90
Segmental relaxation
Tg/T
0.95
1.00
Dynamics and Functions of Biopolymers
November 2009
The main goal is fundamental understanding of dynamics in proteins, RNA and
DNA, and relationship between molecular motion and functions of biological
macromolecules.
Recent finding:
We unravel the nature of the dynamic
transition in biological macromolecules
[Phys.Rev.Lett. 100, 108103 (2008); J.Chem.
Phys. 128, 195106 (2008)].
Understanding the influence of solvents on protein dynamics, activity and stability
is another goal of our research.
It is important for preservation of protein based products (pharmaceuticals,
vaccines, food additives), cells and tissues. We designed a formulation where
proteins can be preserved at room temperature up to ~10 years!!!
Back
Nano-composite and Nano-structured Materials
November 2009
Mechanical Properties of Viruses
Localized mode provides estimate:
Frequency (GHz)
VT1.45±0.1 km/s
500nm
Sub-monolayer WIV
Si
Si
Virus
Virus
0
Localized
(isolated WIV)
6
4
Propagating
(assembled WIV)
2
4
8
12
16
20
24
-1
Q|| (mm )
Q||=24
-10
8
0
Q||=20
-20
10
10
20
Propagating and localized modes provide
consistent estimates of the elastic constants.
Virus appears to be stiffer than hard plastics
Frequency (GHz)
Back
Phys.Rev.E 78, 21907 (2008)
Nano-optics, Plasmonics
We are developing:
Apertureless near-field optics based on
local enhancement of optical signals in
the vicinity of plasmon particles (e.g.
Ag, Au).
November 2009
AFM tip
Laser beam
Plasmon particle
Enhanced field
Near-field ~10 nm
Laser spot ~1 mm
Far-field
Chemical mapping with ~20 nm lateral resolution
PMMA
300nm
SiO2
PMMA
300nm
250nm
SiO2
250nm
30nm
30nm
Si
CdS film
180nm
Topography
Topography
60nm
0nm
0nm
180nm
1200
0
Raman
Raman
Back
0nm
2000nm