Exponential Shear Flow of Linear, Entangled Polymeric Liquids

A previously proposed reptation model is used to interpret exponential shear flow data taken on an entangled polystyrenesolution. Both shear and normal stress measurements are made during exponential shear using mechanical means. The model iscapable of explaining all trends seen in the data, and suggests a novel analysis of the data. This analysis demonstrates thatexponential shearing flow is no more capable of stretching polymer chains than is inception of steady shear at comparableinstantaneous shear rates. In fact, all exponential shear flow stresses measured are bounded quantitatively by stressmeasurements taken during inception of steady shear. Information taken from the model about chain stretching suggests thatnormal stress measurements are strong indications of stretching, whereas shear stress measurements are indicative of bothchain stretching and segment orientation.