(142aa) Viscoelastic Properties of Entangled Polymer Melts From Particle Rheology Simulations

Particle microrheology has become a well-established technique for the experimental determination of micro-scale viscoelastic properties of complex fluids.  Particle motion at the nanoscale and its relation to the medium viscoelastic properties is of interest for several applications in medical and materials sciences.  The viscoelastic properties at these length and time scales are strongly influenced by the specific chemical interactions in the system.  Molecular simulations can explicitly account for these chemical interactions within the system to accurately capture the dynamics at time and length scales that are much lower than those that can be accessed in microrheology. 

Recently we showed that¹ the particle motion in a melt of short polymer chains as obtained by molecular simulations can be analyzed by using a treatment which considers it as stochastic dynamics in a continuum medium to yield the storage (G’) and loss (G’’) moduli of the medium.  Specifically, both passive and active particle rheology approaches were used to determine the frequency dependence of G’ and G’’ for a polymer melt represented by short, unentangled bead-spring chains of length 20.  An important contribution of that work was the demonstration that particle and medium inertia need to be explicitly accounted for in such an analysis of particle motion at the nanoscale.  In this work, the particle rheology simulation approach is extended to a system consisting of long, entangled polymer chains.  Simulation results are used to investigate the rich physics in this system that follows from the interplay of the length scales represented by the particle size, chain tube diameter and the chain size.

1.  M. Karim, S. C. Kohale, T. Indei, J. D. Schieber, and R. Khare, submitted.