Abstract
Rheology and stress relaxation dynamics of a well-characterized, entangled polystyrene/diethylphthalate solution are investigated during start-up and following cessation of steady shear flow. Rheological measurements designed to probe the effect of flow-induced changes in polymer relaxation time on properties form the main focus of this study. At shear rates γ intermediate between the reciprocal terminal relaxation time τd0−1 and reciprocal longest Rouse relaxation time τRouse−1, we find that both convective and nonconvective processes accelerate molecular relaxation in entangled polymer liquids. The former processes are described well by the multimode convective constraint release model of Ianniruberto and Marrucci (2002), but the latter ones are not. At shear rates γ<τRouse−1, the nonconvective processes give rise to a two-stage relaxation mechanism following cessation of steady shear flow. The first stage of relaxation is characterized by a time constant τRecv 1 that is over an order of magnitude gre...
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