A thermodynamic analysis of gas sorption-desorption hysteresis in glassy polymers

Abstract

Sorption-desorption isotherms for carbon dioxide in polycarbonate, tetramethylpolycarbonate, hexafluoropolycarbonate, and poly (vinyl benzoate) were fitted using the glassy polymer lattice sorption model (GPLSM). The model requires sorptive dilation data to account properly for lattice compressibility. Using polymer segment-segment interaction energies from the sorption isotherms, the desorption isotherms were fitted with only a single adjustable parameter, the Henry's law constant. Differences in Henry's law constants between sorption and desorption were explained in terms of the unoccupied volume before and after the sorption-desorption process and the "volatility" of the gas in the local polymer environment at infinite dilution.

Differential water sorption studies on KevlarTM 49 and as-polymerised poly (p-phenylene terephthalamide): adsorption and desorption isotherms

“…This hysteresis cannot be observed using integral adsorption studies, as conducted by Fukuda et al (1991). In the case of polymers, gas adsorption and desorption hysteresis has only been measured for polymers in the glassy state (Conforti and Barbari, 1993). A full review of the literature highlights the large number of attempts that have been made to describe sorption in glassy polymers, from phenomenological models, such as the Dual-Mode Sorption (DMS) (Barrer et al, 1958;Michaels et al, 1963), the continuous site (Weiss et al, 1992), the gas-polymer matrix (Raucher and Sefcik, 1983), and the concentration-temperature superposition model (Mi et al, 1991), to thermodynamically based, and predictive models (Lipscomb, 1990;Conforti and Barbari, 1993;Doghieri and Sarti, 1996).…”

“…A full review of the literature highlights the large number of attempts that have been made to describe sorption in glassy polymers, from phenomenological models, such as the Dual-Mode Sorption (DMS) (Barrer et al, 1958;Michaels et al, 1963), the continuous site (Weiss et al, 1992), the gas-polymer matrix (Raucher and Sefcik, 1983), and the concentration-temperature superposition model (Mi et al, 1991), to thermodynamically based, and predictive models (Lipscomb, 1990;Conforti and Barbari, 1993;Doghieri and Sarti, 1996). For these latter thermodynamically based models, hysteresis is seen as a manifestation of the long relaxation times associated with the non-equilibrium nature of the glassy state (Conforti and Barbari, 1993), one where the amorphous component of the polymeric material undergoes deformation as a result of the accommodation of the penetrant. These theories base themselves upon the dilation of the polymer during sorption, and so in order to conduct an analysis using these models it is necessary to measure the polymer-swelling behaviour.…”

Rapid fabrication of MOF-based mixed matrix membranes through digital light processing

“…The gas adsorption measurements using CO 2 as a probe molecule further corroborate this observation ( Figure S27). Despite the chemical differences in the acrylate systems employed as matrix precursor, shapes of adsorption isotherms reveal large sorption-desorption hysteresis loops along a wide range of pressures as a common attribute of glassy polymers 49 albeit severe divergence in a total adsorption capacity from 0.01 mmol•g -1 for T-to 0.14 mmol•g -1 for U-component and ~0.17 mmol•g -1 for 2/3T+1/3U mixture ( Figure S27A).…”

Determination of thermodynamic properties by supercritical fluid chromatography

“…At higher pressures, the swelling isotherms [159,137] and the sorption isotherms [137] deviate from linearity to produce S-shaped patterns, especially at temperatures not far above the critical point of the gas. Unlike the glassy polymers [143,160], the rubbery siloxanes [143,23] do not display hysteresis during the sorption/desorption cycles. In a PDMS elastomer filled with glass beads, both elastomer-filler interfacial restrictions on sorptive dilation and volumetric restrictions on sorptive dilation reduce the CO 2 sorption capacity of the PDMS elastomer [161].…”