Variable-Connectivity Monte Carlo Algorithms for the Atomistic Simulation of Long-Chain Polymer Systems

Abstract

Recently, our ability to equilibrate atomistic models of synthetic polymers and biopolymers has been significantly enhanced through the development of Monte Carlo schemes employing moves which modify the connectivity of atoms along the chains. In this chapter, the geometric “bridging” construction underlying these moves is explained and the statistical mechanical underpinnings of Monte Carlo algorithms employing these moves to sample various, appropriately designed, ensembles are discussed. Concerted rotation, directed internal bridging, end-bridging, directed end-bridging, scission-fusion, double bridging, intramolecular double rebridging moves, and their combination with parallel tempering are developed in some detail. Results are presented from applying the connectivity-altering Monte Carlo algorithms to predict volumetric behaviour, packing, chain conformation and entanglement properties in long-chain synthetic polymer melts (polyethylene, polypropylene, polyisoprene); melt elasticity and birefringence under conditions of steadystate flow; sorption equilibria of alkanes in polyethylene melts; and composition profiles at solid/polymer interfaces strengthened with grafted polymer chains. The molecular-level insight gained from these calculations is discussed, as is the role of the new algorithms as tools for the development of hierarchical modelling approaches to structure - processing - property - performance relations in polymer systems.