Gas Transport Properties of Poly(dimethylsiloxane)-Silica Nanocomposite Membranes

Loading impermeable nanoparticles into select ultra-high free volume (UHFV) glassy polymers has been shown to improve membrane permeability and selectivity by increasing the membrane’s free volume.   However, the cause of this free volume increase has yet to be determined, and is thought be a result of polymer chain packing disruption, free volume inherent in the added nanoparticles, or interfacial voids.  To explore the mechanism by which free volume increases, rubbery poly(dimethylsiloxane) [PDMS] composite membranes loaded with silica nanoparticles of varying sizes were solution cast subjected to oxygen, nitrogen, helium, and carbon dioxide single-gas permeation experiments. All sizes of silica filler decreased composite membrane permeability to within error of the expected Maxwell permeation value, implying that the permeation increase seen in UHFV glassy polymers is due to polymer chain packing disruptions.