Dynamics of polyethylene melts studied by Monte Carlo simulations on a high coordination lattice

Abstract

A detailed comparison is made between the experiment, prior simulations by other groups, and our simulation based on a newly designed dynamic Monte Carlo algorithm, on the dynamics of polyethylene (PE) melts. The new algorithm, namely, noncross random two-bead move has been developed on a high coordination lattice (the 2nnd lattice) for studying the dynamics of realistic polymers. The chain length (molecular weight) in our simulation ranges from C40 (562 Da) to C324 (4538 Da). The effects of finite chain length have been confirmed and significant non-Gaussian statistics evidently results in nonstandard static and dynamic properties of short PE chains. The diffusion coefficients scale with molecular weight (M) to the À1.7 power for short chains and À2.2 for longer chains, which coincides very well with experimental results. No pure Rouse scaling in diffusion has been observed. The transitional molecular weight to the entanglement regime is around 1500 Da. The detailed mean square displacements of middle bead (g1) are presented for several chain lengths. The reptation-like slowdown can be clearly observed only above M $ 2400 Da. The slope 0.25 predicted by the theory for the intermediate regime is missing; instead a slope close to 0.4 appears, indicating that additional relaxation mechanism exists in this transitional region. The relaxation times extracted by fitting the autocorrelation function of end-to-end vectors with reptation model scale with M to 2.5 for long chains, which seemingly conflicts with the scaling of diffusion.

Modeling of Entangled Polymer Diffusion in Melts and Nanocomposites: A Review

“…The scaling relation of D∝N−2.1 which was very close to the experimental prediction, was predicted over a range of melt densities [137]. A scaling relation of D∝N−2.2 was calculated for PE melts [138] and the start of crossover to reptation regime was observed for N>85 monomers. A different lattice Monte Carlo algorithm for bulk polymer melts had been developed by Shaffer [139].…”

Effect of Stereochemistry on Diffusion of Polypropylene Melts: Comparison of Simulation and Experiment

“…Dynamical Monte Carlo simulations of diffusion in the polypropylene melt system at fixed molecular weight M n as a function of the probability of meso diads ( P m ) have been comprehensively described in a previous publication . Briefly, the coarse-grained model is based on a high-coordination (second-nearest-neighbor diamond) lattice, with each C 3 H 6 monomer (42 g/mol) represented as a bead placed at the stereochemical center; any snapshot in the simulation can be easily reversed to the atomistic detailed chain. Short-range interactions between bonded beads are based on the rotational isomeric state model according to the stereochemistry of a particular dyad as previously parametrized for polypropylene .…”

Systematic coarse-graining of the dynamics of entangled polymer melts: the road from chemistry to rheology

“…For the dynamics local Monte Carlo moves, including a crankshaft move, were introduced. Recently the dynamical updates have been redesigned to study the mean-square-displacement in polyethylene melts [70] and in bidisperse polyethylene melts [71].…”