Journal of Rheology, Vol.61, No.2, 253-264, 2017
Molecular mechanisms of interfacial slip for polymer melts under shear flow
Interfacial slip plays a crucial role in a variety of fluid dynamics problems occurring in practical polymer processing, lubrication, adhesion, nanocomposites, etc. Despite many research efforts, a fundamental understanding of the underlying molecular mechanisms and dynamics is still lacking. Here, we present the intrinsic molecular characteristics of the slip phenomena by using atomistic nonequilibrium molecular dynamics simulations of polyethylene melts under shear flow. Our results identify three distinctive characteristic regimes with regard to the degree of slip and reveal the underlying molecular mechanisms for each regime: (i) the z-to-x chain rotation mechanism in the vorticity plane in the weak flow regime, which effectively diminishes the wall friction against chain movement along the flow direction, (ii) the repetitive chain detachment-attachment (out-of-plane wagging) and disentanglement mechanism in the intermediate regime, and (iii) irregular (chaotic) chain rotation and tumbling mechanisms in the strong flow regime. The second and third regimes can be classified as dynamically stable and unstable, respectively. The present findings would greatly help us comprehend the general characteristics of the interfacial rheological phenomena of polymeric materials. (C) 2017 The Society of Rheology.