80th Annual Meeting of the APS Southeastern Section
Volume 58, Number 17
Wednesday–Saturday, November 20–23, 2013;
Bowling Green, Kentucky
Session EC: Soft Matter, Complex Fluids and Polymers in the Southeast, Biophysics: Biomechanics and Cellular Mechanics
8:30 AM–12:48 PM,
Friday, November 22, 2013
Room: 2
Chair: Robert Cohn, University of Louisville
Abstract ID: BAPS.2013.SES.EC.1
Abstract: EC.00001 : Dynamics of Particles in Soft Matter*
8:30 AM–9:06 AM
Preview Abstract
Abstract
Author:
Michael Rubinstein
(University of North Carolina)
Can the properties of materials be deduced from the analysis of the
trajectories of probe particles diffusing through them? The anomalous
diffusion of a particle in complex media could be due to three fundamental
reasons: (1) Viscoelastic response of the medium to the deformation imposed
on it by the moving particle; (2) The particle could be attracted to some
regions of heterogeneous medium and be temporary localized in these ``sticky''
regions; (3) The particle is repelled from some regions of the medium and
has to go over different energy barriers in order to diffuse through this
medium. Can one determine which of these fundamental reasons cause the
anomalous diffusion? We propose a method of analyzing particle trajectories
to answer this question and to determine the corresponding properties of
complex media such as distribution of relaxation times or energy
distribution of attractive regions.
We use scaling theory to derive the time dependence of the mean-square
displacement \textless r$^{2}$(t)\textgreater of a probe nanoparticle in
polymer solutions and melts. We distinguish several qualitatively different
cases depending on the size d of the particle in comparison to solution
correlation length $\xi $ and tube diameter a for entangled polymer liquids.
We also describe a hopping mechanism for diffusion of particles larger than
mesh size of polymer solids (networks and gels).
We solve activated hopping model in which particle experiences thermally
activated jumps between neighboring wells of different energy depths. We
find that the particle diffusion is ordinary Brownian (not anomalous) if the
width of the distribution of well energies $\Delta U$ is smaller than thermal
energy \textit{kT}. In the opposite case ($\Delta $\textit{U\textgreater kT}) we discover the surprising result
that although jumps between neighboring wells are completely random and
uncorrelated, the particle displacements during consecutive time intervals
are correlated. The source of these correlations is that the particle can be
located in the same well during both time periods. As the result, while the
mean square displacement of the particle is still Brownian, the distribution
of displacements is non-Gaussian and is almost exponential.
*This research was carried out in collaboration with Dr. Sergey Panyukov and supported by National Science Foundation and National Institutes of Health.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2013.SES.EC.1