Analysis of experimental data for polystyrene orientation during stress relaxation using semigrand canonical Monte Carlo simulation

Monte Carlo simulation in the semigrand canonical ensemble is used to construct molecular models of atactic polystyrene samples that are quenched in nonequilibrium states at various times following the cessation of steady shear flow. Experimental data collected by slow magic angle spinning DECODER NMR on quenched, oriented samples prescribe a measure of the residual orientation of chain repeat units after shear and its subsequent decay with time. By speciating the system in orientation space, a series of semigrand canonical Monte Carlo simulations describe the detailed molecular conformational changes that occur in stress relaxation over the time scale of seconds and minutes. The general method of reconstructing molecular conformations from orientation data is also illustrated with several test cases using simple chain models.