Abstract
Abstract Glasses are known to undergo spontaneous densification during isothermal annealing. This volume recovery process, which is also an enthalpy recovery process, can be viewed as the collapse of highly disordered sites or ‘defects’. We have modelled this physical ageing as a diffusion process in which the positive density fluctuation defects are annihilated by the corresponding negative ones. The diffusion constant depends on the concentration of defects, and each diffusion molecular jump induces hierarchically correlated molecular rearrangements which conform to a stretched exponential law. Good agreement was obtained between the theoretical and experimental volumes as well as enthalpy recovery results for poly(vinyl acetate) including the memory experiment and the variation of the effective relaxation time.
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