Molecular Dynamics Simulation Study of Nonconcatenated Ring Polymers in a Melt: II. Dynamics

TL;DR

This study uses molecular dynamics simulations to analyze the unique dynamic behavior of nonconcatenated ring polymers in a melt, revealing faster diffusion and stress relaxation compared to linear polymers, with results deviating from classical models.

Contribution

It provides new insights into the dynamics of ring polymers, showing their faster diffusion and relaxation, which differ from traditional polymer models.

Findings

Ring polymers diffuse faster than linear polymers.

Mean-square displacement shows sub-diffusive behavior beyond gyration radius.

Zero-shear viscosity scales as approximately N^1.4, weaker than linear chains.

Abstract

Molecular dynamics simulations were conducted to investigate the dynamic properties of melts of nonconcatenated ring polymers and compared to melts of linear polymers. The longest rings were composed of N=1600 monomers per chain which corresponds to roughly 57 entanglement lengths for comparable linear polymers. The ring melts were found to diffuse faster than their linear counterparts, with the self-diffusion coefficient for both architectures scaling as approximately N to the -2.4 power for large N. The mean-square displacement of the center-of-mass of the rings follows a sub-diffusive behavior for times and distances beyond the mean-square gyration radius, neither compatible with the Rouse nor the reptation model. The rings relax stress much faster than linear polymers and the zero-shear viscosity was found to vary as approximately N to the 1.4 power which is much weaker than the N to the 3.4 power of linear chains, not matching any commonly known model for polymer dynamics when compared to the observed mean-square displacements. These findings are discussed in view of the conformational properties of the rings presented in the preceding paper (DOI: 10.1063/1.3587137).