Dynamics of Entangled Polyethylenes under Shear via Single-Chain in Mean-Field Simulations

K. Ch. Daoulas (Georg-August Universität, Germany), B. J. Edwards (University of Tennessee, USA), B. Khomami (University of Tennessee, USA), Jun Mo Kim (University of Tennessee, USA), Martin Kröger (ETH-Zürich, Switzerland), and M. Müller (Georg-August Universität, Germany)

The simulation of long-chain entangled polymers under flow conditions, either using nonequilibrium Monte Carlo (NEMC) or molecular dynamics (NEMD), on top of a detailed atomistic representation of the polymer melt, is generally too computationally intensive to be tractable using contemporary hardware and modeling algorithms. Thus, to date, only relatively short-chain, unentangled fluids have been simulated using either NEMC or NEMD. In this project, issues related to computational tractability are avoided by employing the recently developed Single-Chain in Mean-Field (SCMF) simulation approach, in conjunction with NEMC simulation methodology. Specifically, the polymer melt is represented on a mesoscopic level via a system of bead-spring polymer chains in the (N,V,T,a) ensemble, where a represent the strength of the applied flow field. The non-bonded interactions are captured via a quadratic compressibility term, originally introduced by Helfand and Tagami. The number of entanglements per chain is controlled by properly selecting the equilibrium invariant degree of polymerization. The entanglement behavior as a function of chain length, as obtained from SCMF simulations of the coarse-grained model under equilibrium conditions, is compared with the predictions of atomistic simulations available in the literature. Afterwards, NEMC simulations under an applied shear flow are performed to obtain steady-state polymer configurations at varying field strengths, and then these configurations are analyzed using the topological analysis scheme developed by Kröger to estimate the degree of chain entanglement.