Overaging in Glassy Polymers within a Wide Range of Temperature

Mechanical deformation is known to affect the stability of glassy systems. Some studies report that small-amplitude loading leads to overaging, while large-amplitude loading rejuvenates the system. Recent experiments, however, have shown no overaging effect in lightly cross-linked poly(methyl methacrylate) (PMMA) glasses, raising concerns about previous simulation results. Given the importance of understanding physical aging, this work uses coarse-grained molecular dynamics simulations to examine the impact of cyclic loading/unloading on glassy polymers. The results indicate that overaging occurs in glassy polymer systems only below the Vogel–Fulcher–Tammann temperature (T_VFT). Above T_VFT, mechanical perturbations with amplitudes below the critical strain significantly accelerate the structural relaxation. Counterintuitively, these perturbations have minimal effect on inherent energy and all examined structural parameters, while particle mobility shows a clear proportional enhancement and increased spatial correlation.