Stress Relaxation of Polymer Solutions under Large Strain: Elastic Recovery after Partial Stress Relaxation

Constrained elastic recovery of shear strain was measured after partial stress relaxation for a concentrated solution of polystyrene in chlorinated biphenyl. A constant torsional shear strain s was applied to the sample held in a cone-plate sample holder during the period of-tl<t<0. Then the shear stress was removed by releasing the clamp tightening the cone so that the sample was al-lowed to undergo a torsional shear deformation by itself. The elastic recovery yR(t, t1, s) was evaluated from the rotation angle of the cone measured as a function of time t. It increased and approached the ultimate value yR (00, ti, s) more rapidly when the period of relaxation ti was shorter. A large fraction of the original strain s was recovered only when the initial strain s as well as ti was very small. The effects of varying ti and s on yR (co, tl, s) /s were similar to those on the strain-dependent relaxation modulus G(ti, s) (=stress at t=0 divided by s). When t1 was longer than a certain time r', the ratio rR=[yR(m, t1, s)/s]/lim[yR (co, tl, s)/s] was independent of ti and was approximately equal to th