Polymer Solutions and Melts: Viscosity, Diffusion, and Elasticity

Abstract

In an empirical attempt to extend the rubberlike liquid temporary-junction network theory to polymeric liquids whose viscosity η depends on shear rate γ, it is assumed that, in steady shear flow, the sample-average strand lifetime may depend on γ, and that, for linear polymers of a given molecular weight M, is inversely proportional to the self-diffusion coefficient D in a liquid at rest. It is assumed that the plateau modulus G 0 may be used to determine the strand concentration ν. Literature data for molten polystyrene and for a 15% solution of polystyrene in toluene give approximate superposition of the curves for σ/G 0 vs γ/D, where σ denotes the shear stress ; curves for σ vs γ differ by a factor of about 10 000. Curves for G 0 (N 1 - N 2 )/σ 2 vs σ/G 0 are about 100 times closer together than the corresponding curves for (N 1 - N 2 )/σ 2 vs σ, but do not superpose ; this suggests that 2 / 2 depends on the polymer concentration. N 1 and N 2 denote the first and second normal stress differences.