A novel nanocomposite membrane, poly dimethyl siloxane (PDMS)/Au was prepared for CO2/CH4 separation. Synthesis route of stabilized nano particle are reported, and their presence are characterized by UV-visible spectroscopy and Transmission Electron Micrograph (TEM). The hybrid membrane is characterized morphologically by scanning electron microscope (SEM) and the change in inter-segmental distance due to filler loading by wide angle X-ray diffraction patterns (WAXD). The structure of capping agent on Au nanoparticles and its surface chemistry enables dispersion in PDMS matrix were analyzed using FTIR, XPS, EDX, TGA and DSC. The gas transport properties are investigated by single gas permeation and sorption experiments at different pressures and temperatures. The effect of filler loading on permselectivity, diffusivity selectivity and solubility selectivity is reported for CO2/CH4 separation.

The kinetic diameter of penetrant molecules used in the gas permeation study are of the order CO2 (3.3 Å) < CO (3.76 Å) < CH4 (3.8 Å). The selectivities of pure PDMS and various loading levels of Au/PDMS nanocomposite are reported. As expected the pure polymer shows permeation to gas molecules in the order of their kinetic diameter i.e., CO2 is more permeable in pure polymer and the selectivity of CH4 and CO is close to unity (equally permeable). But for the Au/PDMS, there is a reverse selective phenomenon of CO2 at its percolation threshold (CO2 is less permeable compared to higher kinetic diameter counterparts CO & CH4). We hypothesize CO2 has a quadrupole moment and the inter-connectivity of free volume elements enabled by Au NPs must have restricted CO2 movement. Also CO2 is expected to be more soluble in polymer with polar group, but the interaction of PDMS and Au NPs could have reduced the polarity of hybrid membrane. Further work is proceeded to conclude the peculiar phenomena of the above preliminary results.