Effect of Short-Chain Branching on Interfacial Polymer Dynamics under Shear Flow

Abstract

We present a detailed analysis on the effect of short-chain branches on the structure and dynamics of interfacial chains using atomistic NEMD simulations of confined polyethylene melts. The intrinsically fast random motions of the short branches lead to a compact structure against the imposed flow field, compared with the corresponding linear polymer. Such mobile short branches for the SCB polymer further induce a weaker out-of-plane wagging dynamics of interfacial chains with curvy backbone structures in the intermediate flow regime. Through the contribution of short branches to the interfacial friction between chains and the wall, the SCB polymer shows a nearly constant behavior in the degree of slip (ds) in the weak-to-intermediate flow regime. In the strong flow regime where a tumbling occur via collisions between interfacial chains and the wall, an enhancement effect by short branches on the chain detachment from the wall leads to a steeper increase in ds. Remarkably, the SCB chains at interface exhibits rolling mechanisms along the backbone with a half-dumbbell mesoscopic structure at strong flow fields, in addition to a typical hairpin-like tumbling behavior.