Polymer Fractionation at an Interface in Simple Shear with Slip

Using a sliding-plate rheometer, we subject a bimodal high-density polyethylene to simple shear flow with slip and collect the debris left on the surface. Through gel permeation chromatography analysis, we observe surface fractionation occurring in simple shear flow even in the absence of a bulk shear gradient. The surface fractionation and the thickness of the debris film showed a shear rate dependency. The enrichment/depletion transition point was found to be markedly different than that predicted thermodynamically and consistent with previous observations of fractionation on the surface of an extrudate from capillary flow. Our results also highlight the possible occurrence of both adhesive and cohesive slip failure mechanisms, especially at lower shear rates. These new insights provide additional understanding of the physics of polymer slip.