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Recent efforts, fostered by a pioneering work by us, have shown the of multiple steps in the recovery of equilibrium of glasses. Jin and McKenna raise concerns regarding the validity of such scenario alleging that the multiple recovery steps would be an artifact arising from poor temperature control in the oven used for isothermal glass equilibration. We critically discuss Jin and McKenna arguments from both the viewpoints of scrutinizing previous literature data and that of the temperature control in the oven. In doing so, we provide compelling arguments that Jin and McKenna conjectures are unjustified and point out the need for efforts to describe glass dynamics significantly below the glass transition temperature, Tg, by accounting for the presence of different relaxation mechanisms active in glass equilibration.

Macroscopic volume as well as capacitive dilatometry (CD) measurements have been performed on polystyrene/silica nanocomposites during the course of physical aging below the glass transition temperature (Tg). Our results show that the macroscopic volume recovery during physical aging is not affected by the presence of nanofillers, whereas the CD measurements, delivering also information on the polymer matrix density, show acceleration of the recovery with increasing the silica content. Hence, the main outcome of the present work is that the evolution of macroscopic and matrix densities are markedly different in polymer nanocomposites. We interpret these results invoking an equilibration mechanism based on volume holes diffusion. According to this model, excess free volume migration at the polymer/filler interface only modifies the matrix density, thereby explaining the faster recovery detected by CD measurements in comparison to the macroscopic volume one. © 2013 Wiley Periodicals, Inc., The authors acknowledge the University of the Basque Country and Basque Country Government [Ref. No. IT-436-07, Depto. Educación, Universidades e investigación; and Spanish Government (Grant No. MAT2012-31088] for their financial support. V.M.B. acknowledges CSIC for the JAE-Doc contract, cofinanced by the European Social Fund (ESF).