Viscoelasticity of Entangled Polymer Systems with Bimodal Molecular Weight Distributions

Abstract

A blending law for linear viscoelasticity of entangled polymer systems is proposed in the present study, based on the extended tube model theory presented by Doi et al. in 1987. The following conclusions are obtained concerning the relaxation processes of entangled chains in binary blend systems where there are entanglements between the chains of higher molecular weight component.(1) Constraint release due to relaxation of shorter chains in the blends gives rise to the following three changes in and around the long chains: (a) tube renewal, (b) tube dilation or enlargement of the tube diameter, and (c) large scale conformational re-arrangement due to a change in the tube length.(2) When the tube diameter does not change (no dilation case), large scale conformational rearrangement of the long chains does not occur, because equilibration of the tube length due to the constraint release is not necessary in this case.(3) Enlargement of the tube diameter and decrease in the tube length due to the constraint release result in the large scale conformational rearrangement of the long chains.(4) In order to find experimentally a relaxation function associated with the conformational rearrangement, it is necessary to carry out stress relaxation experiments in a restricted regime corresponding to RD box given by the extended tube model theory of Doi et al.