Significant slip can occur during flow of two immiscible polymers due to reduced entanglements at their interface. The slip is of practical importance because of its effect on morphology and adhesion of these multi-phase materials, such as disordered two-phase blends and multilayer films. Using rheological technique, we studied the interfacial slip in co-extruded multilayer films. The viscosity drop of a multilayer sample below the average viscosity of two neat components was observed for both polypropylene/polystyrene and polyethylene/fluoropolymer systems, indicating interfacial slip. Furthermore, the viscosity drop of a multilayer sample increased with the number of layers.
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