Deformation-Induced Mobility in Polymer Glasses during Multistep Creep Experiments and Simulations

Optical photobleaching experiments and molecular dynamics computer simulations were used to investigate changes in segmental mobility during tensile creep deformation of polymer glasses. Experiments were performed on lightly cross-linked PMMA, and the simulations utilized a coarse-grained model. For both single-step and multistep creep deformations, the experiments and simulations show remarkably similar trends, with changes of mobility during deformation exceeding a factor of 100. Both experiment and simulation show a strong correlation between strain rate and mobility in single-step creep. However, in multistep creep, the correlation between strain rate and mobility is broken in both experiment and simulation; this emphasizes that no simple mechanical variable is likely to exhibit a simple relationship with molecular mobility universally. Both simulations and experiments show many features that are inconsistent with the Eyring model.