A sorption and dilation investigation of amorphous glassy polymers and physical aging
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The goal of this work was to investigate the effect of physical aging on penetrant sorption and dilation in glassy polymers. At the present time, this topic is fundamental in nature but may be relevant to previously observed declines in the productivity of polymeric gas separation membranes. Though physical aging is well known to occur in glassy polymers, it is often neglected in most contexts. However, since gas sorption and diffusion occurs on a molecular scale, reduction of unrelaxed volume due of physical aging may have a large impact on the macroscopically observed manifestations of these phenomena. In addition to experimental investigations of the effect of physical aging on the polymerpenetrant environment, various models of sorption and dilation are studied. Of the numerous models available in the literature, the theory of dual mode sorption, Sanchez-Lacombe lattice fluid equation of state and sitedistribution model have previously demonstrated notable success and are applied to three polymers of varying chain flexibility: Matrimid® , Ultem® and Lexan® (Tg = 313, 215 and 150°C respectively). Since the lattice fluid equation of state is intend for use on equilibrium media, only partial descriptions of solubility are expected. A variation of the Sanchez-Lacombe equation of state which takes into account the non-equilibrium nature of the glassy state, suitably called the NonEquilibrium Lattice Fluid model, is also considered. In this work, the sorption and dilation data were used to study the presence of unrelaxed volume in glassy polymer materials and how it is affected by physical aging. A variety of other characterizational techniques were explored as well. Substantial changes in the sorption, dilation and CO2 partial molar volume due to physical aging were observed for bulk films of Matrimid® and Lexan® , but not for Ultem® . Gas solubility was found to be lower in thin ( l =0.1mm) Matrimid® films than in thick films (l =25.4mm) giving rise to lower values of the so-called “Langmuir sorptive capacity” for the thinner sample. This particular result along with other experimental observations made in this work support claims based on the proposed “diffusion of free volume” mechanism of aging that explains thickness dependent phenomena in glassy polymers.