Overaging in\nGlassy Polymers within a Wide Range of\nTemperature

Mechanical deformation is known to affect the stability\nof glassy\nsystems. Some studies report that small-amplitude loading leads to\noveraging, while large-amplitude loading rejuvenates the system. Recent\nexperiments, however, have shown no overaging effect in lightly cross-linked\npoly(methyl methacrylate) (PMMA) glasses, raising concerns about previous\nsimulation results. Given the importance of understanding physical\naging, this work uses coarse-grained molecular dynamics simulations\nto examine the impact of cyclic loading/unloading on glassy polymers.\nThe results indicate that overaging occurs in glassy polymer systems\nonly below the Vogel–Fulcher–Tammann temperature (<i>T</i><sub>VFT</sub>). Above <i>T</i><sub>VFT</sub>, mechanical perturbations with amplitudes below the critical strain\nsignificantly accelerate the structural relaxation. Counterintuitively,\nthese perturbations have minimal effect on inherent energy and all\nexamined structural parameters, while particle mobility shows a clear\nproportional enhancement and increased spatial correlation.