Structural recovery modeling, physical aging

Below Tg (4,5) co-operative molecular processes are usually assumed to be inactive. However, physical ageing implies that conformational changes may be still able to occur if rather infrequently. Structural relaxation processes are observed to be non-exponential and are represented by a continuous distribution or stretched exponential form (d). Thermorheologically simplicity (TRS) implies that the molecular relaxation process has the same form at different temperatures (7) and the validity of this assumption is addressed in this paper. Isobaric volume recovery (8,9) has been described by a single parameter mc el, however all fi ee volume models (10,11) have limitations and a distribution of hole sizes and relaxation times leading to a pseudo-linear theory is a more realistic model(72). Comparison of data fi om various techniques should throw light on the molecular nature of physical agdng. 

Although the basic phenomenology associated with glasses is known and models exist which describe structural recovery and physical aging, researchers are not yet able to predict a priori experimental observations. 

In this article on physical aging, the phenomena associated with structural recovery and physical aging are described, starting with discussion of volume recovery, enthalpy recovery, viscoelastic properties, and failure. There are more in-depth reviews of the phenomena and models associated with the glass transition... 

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