Segment connectivity, chain-length breathing, segmental stretch, and constraint release in reptation models. II. Double-step strain predictions

Predictions for double-step strain flows are presented using a newly proposed reptation theory that accounts for segment connectivity, chain-length breathing, segmental stretch and constraint release in a self-consistent, full-chain theory. In this part of the work emphasis is on double-step shear strains where the secund step is reversed and the imposition time of the second strain is earlier than the estimated retraction time, for which the Doi-Edwards model and single-integral models have been found to be incapable of describing experimental trends. Transient stress relaxation properties of two types of reversing hows, types B and C, have been examined and compared to the predictions obtained from the Doi-Edwards model and a single-integral model. The simulations show excellent agreement with the experimental trends based on recent mechanical and optical measurements. (C) 1998 American Institute of Physics. [S0021-9606(98)52846-2].