Rheology of Entangled Polymeric Systems

Experimental Tests of the Tube-Model Theory of Doi and Edwards

Abstract

This paper summarizes the results of experiments performed for testing the tube-model theory of Doi and Edwards to describe the nonlinear viscoelasticity of entangled polymeric systems. For each concentrated solution of polystyrene of sharp molecular weight distribution, one can determine a characteristic time constant τ_A from the shear stress following step-shear deformations of various magnitudes of shear. The Doi-Edwards theory was revealed to describe well various observed rheological phenomena, provided that the time scale of the phenomenon is longer than τ_A or that the rate of strain is less than τ_k^-1. The experimentally determined quantity τ_A, being proportional to the square of the number of entanglement per molecule, may give a measure of time in which the fluctuation of the chain contour length equilibrates completely. There are some indications that the concept of tube model is consistent with the phenomena at short times or at high rates of strain, for which the theory for the viscoelasticity has not yet been established.