Stress relaxation of polymer solutions under large strain

Abstract

Shear relaxation moduli G(t, s) were measured for various strains s with a relaxometer of the cone-plate type for concentrated solutions of polystyrene in chlorinated biphenyl. The strain was varied from 0.34 to 25 shear units. The time - temperature reduction method was applicable to the shear-dependent relaxation moduli over the temperature range studied (20-50°C) and the shift factor aT was independent of s. When s was very large, log G(t, s) decreased very rapidly with increasing time in two regions of t (two-step relaxation) while log G(t, s) for small s dropped rapidly only at long times (one-step relaxation). The relative rate of decrease of G(t, s) with increasing s was independent of t when t was larger than a certain time, τk. The maximum relaxation time τm was independent of s while the corresponding strength of relaxation Gm was proportional to ID-0.83 when s was large. Here ID is the first invariant of strain.