Pure and mixed gas CH₄ and n-C₄H₁₀ sorption and dilation in poly(dimethylsiloxane)

Pure and mixed gas n-C₄H₁₀ and CH₄ sorption and dilation properties in poly(dimethylsiloxane) (PDMS) are reported at temperatures ranging from -20 to 50 °C. CH₄ partial pressures range from 3.1 to 16 atm, and n-C₄H₁₀ partial pressures range from 0.07 to 1.3 atm. Based on the mixed gas sorption results, the presence of n-C₄H₁₀ in the polymer enhances CH₄ solubility. For instance, at 25 °C, a 10% increase in CH₄ solubility, from 0.50 (pure gas) to 0.55 cm³ (STP)/(cm³ polymer atm), is observed when the n-C₄H₁₀ activity goes from 0 to 0.29. At -20 °C, as n-C₄H₁₀ activity increases from 0 to 0.53, CH₄ solubility increases by almost 35%, going from 0.77 to 1.03 cm³ (STP)/(cm³ polymer atm). In contrast, n-C₄H₁₀ sorption properties in these mixtures are not measurably affected by the presence of CH₄. The n-C₄H₁₀/CH₄ solubility selectivity in PDMS increases as temperature decreases and as n-C₄H₁₀ activity in the mixture increases. For example, at 25 °C, the solubility selectivity increases from 52 to 60 as n-C₄H₁₀ activity increases from 0.11 to 0.34. At 0 °C, n-C₄H₁₀/CH₄ solubility selectivity increases from 84 to 105 as n-C₄H₁₀ activity increases from 0.09 to 0.33. Pure and mixed gas dilation results are used to calculate partial molar volumes of CH₄ and n-C₄H₁₀ in the polymer. Dilation isotherms in mixtures agree with estimates based on pure gas sorption and dilation measurements.