(180s) Configuration-Dependent Friction Coefficient in Tube Models for Entangled Polymers

We have incorporated a configuration-dependent friction coefficient (CDFC) in the full-chain stochastic tube model for entangled melts and solutions developed by Xu, Denn, and Schieber [J. Rheology 50, 477-494 (2006)] to account for microstructural change of the tube away from equilibrium. The simulation results from the modified model significantly reduce the deviation from experimental data in shear, and they also agree well with extensional data for entangled solutions, including an initial negative 0.5-power dependence of the steady extensional viscosity on extension rate.
We have also applied CDFC to the Mead-Larson-Doi model [Macromolecules31, 7895-7914 (1998)] and obtained improved predictive performance at high deformation rates without the need to treat the extensibility parameter as an adjustable parameter, reinforcing the idea that there is a structural change in the tube far from equilibrium that accelerates relaxation processes.
Finally, since various molecular models make fundamentally different assumptions about the effect of deformation on the entanglement density but are equally good in rheological predictions, we explored the effect of the dynamics of the entanglement density by changing the entanglement assumptions in the stochastic model.