Chain Dynamics of Ring and Linear Polyethylene Melts from Molecular Dynamics Simulations

The dynamical characteristics of ring and linear polyethylene (PE) molecules in the melt have been studied by employing atomistic molecular dynamics simulations for linear PEs with carbon atom numbers N up to 500 and rings with N up to 1500. The single-chain dynamic structure factors S(q,t) from entangled linear PE melt chains, which show strong deviations from the Rouse predictions, exhibit quantitative agreement with experimental results. Ring PE melt chains also show a transition from the Rouse-type to entangled dynamics, as indicated by the characteristics of S(q,t) and mean-square monomer displacements g1(t). For entangled ring PE melts, we observe g1(t) ∼ t0.35 and the chain-length dependence of diffusion coefficients DN ∝ N−1.9, very similar to entangled linear chains. Moreover, the diffusion coefficients DN remain larger for the entangled rings than the corresponding entangled linear chains, due to about a 3-fold larger chain length for entanglement. Since rings do not reptate, our results point t...