The effect of crosslinking temperature on the permeability of PDMS membranes: Evidence of extraordinary CO2 and CH4 gas permeation

It is important for gas permeable membranes, employed in many industrial applications, to have a high permeability as the cost of many processes such as gas separation and sensing directly depend on it. Polydimethylsiloxane (PDMS) has been a widely utilized polymer within permeable membranes as it possesses high intrinsic flux. However, little attention has been placed on the effect of crosslinking temperatures during synthesis. In this work, PDMS membranes were prepared using a range of crosslinking temperatures and evaluated for their gas permeation towards CO2, N2 and CH4. The investigation of the effect of the crosslinking temperature on gas permeation of PDMS membranes revealed an optimum temperature of 75 °C at which the permeability increased (for N2 from 360 to 590 Barrer, for CO2 from 3190 to 3970 Barrer, and for CH4 from 850 to 1000 Barrer). The vibrational and electron beam spectroscopy studies show that at this optimum temperature the structure of polymer chains is relaxed due to the reduction of the crosslinking density and an enhancement in the fractional free volume (FFV) within the polymer matrix, allowing more efficient diffusion of the gas molecules. Eventually, we demonstrate the extraordinary capability of the membranes crosslinked at 75 °C by incorporating them in sensing systems. Remarkably the sensors' response with and without the presence of the improved membrane are nearly the same for CO2 and only show a 30% decrease for CH4. This experiment depicts the strong potential of the developed membrane for efficient, passive and low cost gas phase separation of selected gas species.