Entanglement Relaxation and Release in Hard Chain Fluids during Molecular Dynamics Simulations

Abstract

Discontinuous molecular dynamics simulations are performed on systems containing 32 hard chains of length 192 at three volume fractions, φ = 0.40, 0.45, and 0.50, to investigate entanglement relaxation and release in model polymer melts. The relaxation behavior of the systems is compared to that predicted by the tube model and to that suggested for the release of interchain entanglements, or knots. The mean squared displacement of the chain center of mass, the mean squared displacements of inner, outer, and intermediate segments along the chain, the end-to-end vector autocorrelation function, and the apparent self-diffusion coefficient are calculated over the course of the simulations. The three relaxation times (τe, τR, and τd) predicted by the tube model are estimated in order to determine the extent to which the results exhibit tube confinement. The initial relaxation of chain segments occurs from the ends toward the middle as the tube model predicts. However, different methods for predicting the longe...