The reptation model with segmental stretch

Abstract

Numerical predictions of the Doi-Edwards tube model with segmental stretch and a freely jointed chain spring model are presented for steady two-dimensional flows with a continuously varying degree of extensional and shear character. Our results are obtained from three sets of calculations by considering the effect of the flow-type parameter, the molecular weight and the number of entanglements per chain on the model predictions. The predicted degree of stretch and orientation, as well as specific rheological and optical properties that can be measured experimentally are presented. As anticipated, calculations reveal that the ‘orientational’ dynamics are controlled by the reptative tube disengagement process, whereas the stretching process is controlled by the Rouse dynamics. Inclusion of segmental stretch fundamentally alters the character of the Doi-Edwards model. Calculations reveal that as the flow becomes increasingly extensional in character, significant steady state stretch is predicted with a commensurate modification of the material functions. According to calculated results, it is possible to have significant chain stretching without producing measurable changes in the stress optical coefficient.