MODELING VISCOELASTIC BEHAVIOR OF GLASSES DURING PHYSICAL AGING

The generalization of a multiordering parameter model to treat physica l aging in polymeric glasses is more fully explored. In the past, this model has successfully rationalized most aspects of time dependent vo lume and enthalpy behavior; however, only qualitative agreement betwee n predictions of the generalized model and experiment were previously achieved for physical aging. Now, by paying strict attention to the sp ecific analytical form of the shift factor expression, quantitative pr edictions have been realized for physical aging behavior based on eval uations of the shift factor parameters using volumetric data. The mode l also reproduces the observed behavior of glasses subjected to more c omplex thermal treatment such as those which evoke ''memory'' in glass es, e.g., shift reversal and nonmonotonic variations of the steepness of relaxation curves in the primary transition region.