Sorption and partial molar volume of gases in poly (dimethyl siloxane)

Abstract

SynopsisSorption of N2, 02, Ar, CHI, COz, C2HI, and CzHs in poly( dimethyl siloxane) liquid and rubber and the dilation of the polymers due to sorption of the gases are studied at 25OC under pressures up to 50 atm. In the liquid, the sorption isotherms for low-solubility and high-solubility gases are described by Henry's law and the Flory-Huggins equation, respectively. Gas sorption in the rubber, which contains a 29 wt % silica filler, follows the dual-mode sorption model, though marked hysteresis is observed in the sorption of O2 and CHI. The dilation isotherms increase linearly or exponentially in both polymers with increasing pressure. Considering that gas molecules adsorbed into micropores of the filler particles do not participate in the dilation, partial molar volumes of the dissolved gases in the rubber are determined from data of sorption and dilation. The values are nearly equal to the partial molar volumes in the liquid (48-60 cm3/mol).

High-precision gravimetric technique for determining the solubility and diffusivity of gases in polymers

“…13,15 -20 The correlation in Figure 3 can be the dual-mode type 21 glassy nature of both PVC represented by samples is not as evident during the sorption runs as it is during the desorption runs. The solubility V U g /cm 3 mol 01 Å 0.276 1 V c / 19.8 (9) curves for the two PVC samples are very similar; however, in the glassy region, the values for the For glassy polymers, the solubilities are often UPVC sample are consistently higher than for the expressed by the dual-mode equation 21 filled PVC sample even when the latter results are normalized with respect to 100% PVC. In the…”

“…For CO 2 , r g was terms on the right-hand side are often used to obtained from the IUPAC recommended equation obtain D. However, these techniques are not satof state. 9 For HFC134a, r g was calculated using isfactory as they do not utilize the entire kinetic the equation of state curve.…”

Detailed-atomistic molecular modeling of small molecule diffusion and solution processes in polymeric membrane materials

“…During the PDMS packing process, a mixture of 10 methane and 33 carbon dioxide molecules were inserted, which corresponds to concentrations of 7.8 and 25.6 cm 3 (STP)/cm 3 (polymer), respectively. These numbers are based on experimentally determined solubility parameters 116) .…”

Determination of thermodynamic properties by supercritical fluid chromatography

“…At low pressures of the gas, both the absorbed amount of the gas and the relative change in volume of the polymer phase are proportional to pressure [143,153,154], and the quantitative differences in solubility coefficients among the individual gases are clearly apparent [155]. It appears that replacement of the methyl groups in PDMS by bulkier substituents tends to decrease the low-pressure solubility of CO 2 because of increased stiffness of the siloxane chain and decreased fractional free volume of the polymer [156].…”