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The addition of fumed silica particles to glassy polymers such as PTMSP and Teflon AF 2400 results in an enhancement of gas diffusivity and permeability that is not captured by traditional models for composites because both volume and gas solubility of the composite material are underestimated by the additive rule based on pure component properties. Such effects have been attributed to the creation of additional free volume due to the insertion of filler in the polymeric matrix. In this work, we use the NELF model to relate gas solubility in the composite material to the variations induced by the addition of filler on polymer density and swellability. From these values, the fractional free volume (FFV) increase produced in the polymeric phase by filler incorporation may be evaluated and, in turn, also the diffusivity in the composite material can be calculated as a function of filler content on the basis of its relation to FFV. The gas diffusivity data for n-C 4H 10in AF 2400 and AF 2400-based mixed matrices, as well as those relative to N 2, CH 4, C 2H 6, C 3H 8, and n-C 4H 10in PTMSP, follow closely the correlation found, which contains only one adjustable parameter for each penetrant-polymer couple. [ABSTRACT FROM AUTHOR]

An analysis of the empirical correlations that relate the solubility coefficient of gases at infinite dilution in glassy polymers to penetrant properties has been performed, by considering gas sorption as a succession of three steps:  condensation of the penetrant, dissolution in the equilibrium polymeric phase, and departure of the system from equilibrium. The infinite dilution solubility coefficient is obtained from the contributions of the three steps, the first two of which involve standard equilibrium thermodynamics, while the latter requires nonequilibrium considerations and is described by using the nonequilibrium lattice fluid (NELF) model. The various terms have been evaluated for several gases in polycarbonate, polysulfone, poly(phenylene oxide), and poly(methyl methacrylate). It has been found that the largest term in the expression of solubility is due to condensation, which explains the observed correlation between solubility and critical temperature, while the out of equilibrium contribution to solubility, which generally gives numerical values lower than the condensation term, is in turn more strongly correlated to the penetrant critical volume. [ABSTRACT FROM AUTHOR]

Membranesobtained by adding small amounts (1 wt %) of nanoplateletsof graphene (G) and graphene oxide (GO) to poly(1-trimethylsilyl-1-propyne)(PTMSP) were fabricated with a simple route, and their gas permeabilitywas measured at 30 °C over 9 months. In most cases, variationsof PTMSP permeability due to the addition of filler are limited, whilethe ideal selectivity of CO2/He, CH4/He, andCH4/N2is slightly enhanced by addition of filler.Specific measurements indicate that the CO2and CH4diffusivity are more strongly affected by addition of graphenethan their solubility: such behavior indicates that the filler modifiesmainly the microstructure of the polymer rather than its interactionswith the gas, as it is reasonable. The most significant quantitativeeffect observed after filler incorporation is the reduction of PTMSPaging, that was monitored by studying gas permeability after 9 monthsof aging at room temperature and after annealing at 200 °C. Thereduction of aging observed after adding graphene is more significantthan that obtained with large amounts (up to 20 vol %) of other inorganicfillers, like MgO and TiO2, even though the amount of filleradded in this work is small (<1 wt %). Such behavior, coupled tothe generally favorable effect of filler on gas permeability and selectivity,makes such materials extremely promising for real applications. [ABSTRACT FROM AUTHOR]