Testing the tube model in branched polymers by large-scale computer simulations

Abstract

The tube model has become the basic tool for predicting dynamic and viscoelastic properties of linear polymer melts. However, in the case of more complex branched systems modifications of the original model are needed, since the presence of branch points dramatically modifies the viscoelastic properties in comparison to linear chains. Industrial polymers are mostly architecturally complex. Thus the investigation of their relaxation mechanisms is a highly active area of research from fundamental and applied points of view. Unfortunately, direct information on the microscopic details of the relaxation mechanisms is hardly accessible by experiments. This drawback can be solved by means of computer simulations. With the aid of supercomputers, we have performed large-scale molecular dynamics simulations of strongly entangled bead-spring polymers with complex architectures (stars, H-polymers, combs, Cayley trees,...). In this contribution we aim to shed light on some open questions (tube dilution, “fat bead” approach, hopping of branch points...) of tube-based models for relaxation of branched polymers. The simulation results give strong evidence of long-arm retraction and a late transition to reptational dynamics after relaxation of the short side branches. We quantify, directly from the simulation results, specific values of branch point hopping parameters postulated by tube-based hierarchical models.