Temperature dependence of the adsorption and diffusion of gases in polyvinyltrimethylsilane

Fractal model of the free volume of vitreous poly(vinyltrimethylsilane) from data on gas diffusion

“…However, among all the microholes, only the microholes that satisfy the criterion d p > d mol are accessible for diffusion. This condition is taken into account in traditional gas transfer models [2] and fractal (more precisely, multifractal) models [16]. The accessible fractal free volume can be defined as follows:…”

“…For example, the ratio between the diffusion coefficients D of the PVTMS and PC polymers is equal to ~56 for the H 2 O diffusion and ~33 for the CH 4 diffusion [3]. In order to explain this difference, Volkov et al [2] assumed that the PVTMS structure includes interconnecting microholes with a mean diameter of ~2 Å and a specific size distribution. This assumption requires an explanation.…”

“…It is known [1,2] that vitreous poly(vinyltrimethylsilane) (PVTMS) with a high glass transition temperature T g (~440 K [3]) has a large diffusion coefficient D as compared to the diffusion coefficient of polycarbonate (PC) based on bisphenol A with a close value of the glass transition temperature T g (~423 K [3]). For example, the ratio between the diffusion coefficients D of the PVTMS and PC polymers is equal to ~56 for the H 2 O diffusion and ~33 for the CH 4 diffusion [3].…”

“…However, it is also known [6] that the relative free volume f v even for devitrified polymers does not exceed 0.159. Moreover, the microhole diameter d p ≈ 2 Å given in [2] is too small to provide a considerable increase in the diffusion coefficient for gases, such as Ar, O 2 , or N 2 , whose molecular diameters are equal to or larger than 3 Å [7].…”

Factors defining the selectivity polymer membranes: A fractal model

“…It was repeatedly assumed earlier that the selectivity of polymer membranes by the coefficients of gas permeability1 and the diffusion2 depends on the chain kinetic rigidity. In favor of such assumption several confirmations were cited, but the direct correlation between these properties of polymers is absent.…”