Rheological properties of polymer melt between rapidly oscillating plates: An application of multiscale modeling

Abstract

The behavior of a supercooled polymer melt composed of short chains with ten\nbeads near an oscillating plate are simulated by using a hybrid simulation of\nmolecular dynamics (MD) and computational fluid dynamics (CFD). In the method,\nthe macroscopic dynamics are solved by using CFD, but, instead of using any\nconstitutive equations, a local stress is calculated by using a non-equilibrium\nMD simulation associated at each lattice node in the CFD calculation. It is\nseen that the local rheology of the melt varies considerably in a thin viscous\ndiffusion layer that arises near an oscillating plate. It is also found that\nthe local rheology of the melt is divided into the three different regimes,\ni.e., the viscous fluid, viscoelastic liquid, and viscoelastic solid regimes,\naccording to the local Deborah number $De$, which is defined with the Rouse or\n$\\alpha$ relaxation time, $\\tau_R$ or $\\tau_\\alpha$, and the angular frequency\nof the plate $\\omega$ as $De^R$=$\\omega\\tau_R$ or\n$De^\\alpha$=$\\omega\\tau_\\alpha$. The melt behaves as a viscous fluid when\n$De^R\\lesssim 1$, and the crossover between the liquid-like and solid-like\nregime takes place around $De^\\alpha\\simeq 1$.\n