Using the TNM model to reproduce reported anomalous structural recovery data in light of temperature variability in vacuum oven-based experiments

We report a study on the possible reasons for the apparent two mechanism structural (enthalpy) recovery reported by Cangialosi et al. [Cangialosi, D., Boucher, V. M., Alegría, A., & Colmenero, J. (2013). Physical Review Letters, 111(9), 095701], which challenges the general view of the isothermal structural recovery behavior of glasses being smooth functions of aging time as observed in extensive dilatometric experiments by Kovacs [Kovacs, A. J. (1964). In Fortschritte der hochpolymeren-forschung, pp. 394-507. Springer, Berlin, Heidelberg.], and a second plateau was not reproduced in the work from Koh and Simon [Koh, Y. P., & Simon, S. L. (2013). Macromolecules, 46(14), 5815-5821.] in one year aging experiments. We examine the possibility that the poor temperature control of a typical vacuum oven could explain the anomalous results. We used the Tool-Narayanaswamy-Moynihan (TNM) model of structural recovery to calculate the effect of typical vacuum oven temperature variation on the structural recovery of polystyrene and find that we can reproduce the reported experimental results. The issue of temperature control using a vacuum oven is discussed, and data from thermocouple measurements of temperature at various locations inside a vacuum oven are shown.