On the Influence of Interfacial Slip on Melt Flow Properties of Polymer Blends

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Abstract
Absolute minima in delineations of viscosity against composition is studied. The hypothesis that this anomaly may be caused by low friction interfaces is scrutinized. Selected polymethylmethacrylates (copolymers) and polystyrenes are used as model materials. An interfacial (slip) viscosity is formally defined by considering the interfaces as separate layers in a multilayer sample consisting of alternating thin layers of polymer 1 and polymer 2. For such a multilayer the steady state shear viscosity of the blend at constant shear stress may be written: 1/η = Φ1/η1 + Φi/ηi + Φ2/η2, where ηi, ηi, and η2 are the viscosities of polymer 1, the interface and polymer 2, respectively. Φ1, Φi and Φ2 are the corresponding volume fractions. Using this equation ηi, is found from measurements on multilayer samples. ηi is found to be lower by a factor of 10 than the lowest viscosity of the homopolymers. Domain stability of the model system are investigated. The minima in viscosity-composition plots of well dispersed blends disappear by addition of selected blockcopolymers to the blend. It is concluded that interfaces with low frictional resistance is formed and must be considered when modelling the behavior of polymer blends.

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