Atomistic Simulation of Dynamics of Individual Molecules in Entangled Polymers Undergoing Homogenous Shear and Planer Elongational Flows

摘要

Nonequilibrium molecular dynamics (NEMD) simulations of an entangled C700H1402 linear polyethylene system were performed to investigate the chain dynamics over a wide range of Weissenberg numbers (Wi) under steady shearing flow. Similar to the unentangled (C78H158) and moderately entangled (C400H802) melts examined in prior simulation studies, the distribution of the chain end-to-end distance, |Rete|, at high Wi was bimodal with a peak at low |Rete| which is associated with the dynamical rotation/retraction cycles experienced by individual chains, and a peak at high |Rete| which corresponds to the highly stretched and oriented macromolecules. To understand the underlying physics, the relevant system time scales including the entanglement time, Rouse time, and disengagement time were determined using segmental mean square displacement analysis of the chain molecules. The longest (τd) and rotational (τrot) relaxation times of the system at high Wi were extracted by fitting a functional form of A*exp(-t/τd)cos(2πt/τrot) to the end-to-end vector autocorrelation data. The number of entanglements and other topological features of the liquid were also computed as functions of Wi.