Fluctuating soft-sphere approach to coarse-graining of polymer models

Abstract

We introduce a coarse-grained model for the simulation of the statistical properties of polymeric systems where collections of chain segments are represented by connected soft spheres of fluctuating size. A generic bead–spring model is considered as a test case for this coarse-graining approach. The effective interactions between the soft spheres and the effective free energy that governs the size distribution of soft spheres are determined using analytical calculations or empirical expressions, leading to relatively simple functional forms that facilitate implementation in the simulation code. The validity of this coarse-graining approach is tested on a variety of systems ranging from ideal chains to dilute solutions and melts. The scheme allows to vary the spatial range of coarse-graining in a flexible and consistent way, and turns out to be particularly efficient for polymer melts. The equilibrium properties of the coarse-grained model agree with those of the original bead–spring model. As the coarse graining does not conserve entanglements, the dynamics is restricted to Rouse-like and the considerably accelerated coarse-grained dynamics suggests this approach as particularly promising for the equilibration of large long-chain polymer melts and mixtures.