Crossover from the Rouse to the Entangled Polymer Melt Regime: Signals from Long, Detailed Atomistic Molecular Dynamics Simulations, Supported by Rheological Experiments

Abstract

Results are presented from 300 ns long atomistic molecular dynamics (MD) simulations of polyethylene (PE) melts, ranging in molecular length from C78 to C250. Above C156, the self-diffusion coefficient D is seen to exhibit a clear change in its power-law dependence on the molecular weight (M), significantly deviating from a Rouse (where D ∼ M-1) toward a reptation-like (where D ∼ M-2.4) behavior. The mean-square displacement (msd) of chain segments and the dynamic structure factor is also calculated and the crossover from the Rouse to entangled behavior is again observed above C156. A novel strategy is also developed for projecting atomistic chain configurations to their primitive paths and thereby mapping simulation trajectories onto the reptation model. Results for the friction factor ζ, the zero-shear rate viscosity η0 and the self-diffusion coefficient D are found to be internally consistent and in agreement with experimental rheological data.