When a non-crystallizable polymer is removed from its equilibrium in the liquid state by a sudden decrease in temperature to below the glass transition temperature, it reaches a new glassy, non-equilibrium state. This state has a specific volume and an enthalpy higher than the underlying equilibrium one, so that the volume, under isothermal conditions and in the absence of any external stimulus, decreases over time towards the equilibrium value. This phenomenon is known as structural recovery. Structural recovery effects on other material properties, such as optical or mechanical properties, are known as physical aging. It is also well known that small molecules affect the viscoelastic response of polymers by, for example, depressing the glass transition temperature of the material. Therefore, one can anticipate that a rapid change in plasticizer content such as CO_2 or H_2O would result in a change in the volume and viscoelastic response of the material. Here, we describe previously physical aging results for epoxy films subjected to sequential creep tests after carbon dioxide pressure down-jumps at constant temperature and after temperature down-jumps at constant carbon dioxide pressure. The aging rate for the CO_2-jump was slightly lower than that for T-jump and the retardation time for PCO_2-jump experiments was up to 6.3 times longer than observed in T-jumps (1). The work is extended here by volume recovery measurements on the same epoxy subjected to isothermal PCO_2 jumps. Similar to the temperature jump experiments performed by Kovacs (2), we show the volume recovery responses in different histories as intrinsic isopiestics (constant PCO_2), asymmetry of approach and the memory effect. In addition, we present preliminary results on the sorption/desorption of CO_2 by poly(vinyl acetate) (PVAc). The experiments were performed at 24°C. The desorption of CO_2 by the epoxy showed a glass transition in mass.
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