Carbon dioxide, sorption parameters

The solid line in Fig. 1 represents the sorption isotherm of carbon dioxide in polycarbonate calculated by fitting the solubility expression, eq. (11), to experimental data of Wonders and Paul (15). The best fit to the experimental data was achieved with the parameters ao=7.33cm3(STP)/cm3(polymer)-atm and a = 0.161 cm3(polymer)/cm3(STP). As can be seen in Fig. 1, eq. (11) describes the experimental data over the entire pressure range. The algorithm used to fit eq. (11) to the experimental data is described elsewhere (FI). 

Many computational studies of the permeation of small gas molecules through polymers have appeared, which were designed to analyze, on an atomic scale, diffusion mechanisms or to calculate the diffusion coefficient and the solubility parameters. Most of these studies have dealt with flexible polymer chains of relatively simple structure such as polyethylene, polypropylene, and poly-(isobutylene) [49,50,51,52,53], There are, however, a few reports on polymers consisting of stiff chains. For example, Mooney and MacElroy [54] studied the diffusion of small molecules in semicrystalline aromatic polymers and Cuthbert et al. [55] have calculated the Henry s law constant for a number of small molecules in polystyrene and studied the effect of box size on the calculated Henry s law constants. Most of these reports are limited to the calculation of solubility coefficients at a single temperature and in the zero-pressure limit. However, there are few reports on the calculation of solubilities at higher pressures, for example the reports by de Pablo et al. [56] on the calculation of solubilities of alkanes in polyethylene, by Abu-Shargh [53] on the calculation of solubility of propene in polypropylene, and by Lim et al. [47] on the sorption of methane and carbon dioxide in amorphous polyetherimide. In the former two cases, the authors have used Gibbs ensemble Monte Carlo method [41,57] to do the calculations, and in the latter case, the authors have used an equation-of-state method to describe the gas phase. 

The sorption of supercritical solvent and flic resulting swelling could be very high, for example around 30% and 20% respectively for carbon dioxide in polymethylmefliacrylate (PMMA). In such instances, the experimental information could be summarized using polymer equation of states such as Sanchez-Lacombe where a single mixture fitting parameter is used. ... 

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