Structural relaxation above the glass temperature: pulse response simulation with the Narayanaswamy Moynihan model for glass transition

Abstract Structural relaxation is understood as the relaxation from a non-equilibrium glass state towards the equilibrium, and not from only the non-ergodic glass zone of the equilibrium liquid to the ergodic liquid or flow zone of the equilibrium liquid (response across the dynamic glass transition). Structural relaxation is, therefore, usually connected with temperatures below the glass temperature Tg. For short pulses or large heating or cooling rates T we get, however, structural relaxation also in a certain temperature range above Tg. Non-linearity for structural relaxation and equilibrium response are compared. Single and double pulse responses above the glass temperature are analyzed by simulation with the Narayanaswamy Moynihan model. The model substance parameters are chosen to be similar to those of polyvinylacetate. For steep pulse flanks of | T |=480 K/min (as, e.g., for optical experiments), we obtain surprisingly long exchange times, e.g., up to 7 s at a temperature 10 K above Tg, where the τKWW equilibrium time of the α process is only 0.52 s.