Comparison of gas diffusion in poly[1-(trimethylsilyl)-1-propyne] and poly(dimethylsiloxane) by atomistic modeling

Diffusion of light gases in poly[1-trimethylsilyl)-1-propyne] (PTMSP) and p oly(dimethylsiloxane) (PDMS) was investigated by a molecular dynamics techn ique. Diffusion coefficients of helium and neon in PTMSP were larger than t hose in PDMS due to the larger free volume fraction of PTMSP in spite of it s higher chain rigidity. This indicates that the amount of the free volume fraction is a more important factor than the redistribution of the free vol ume for the diffusion of light gases in either polymer. conformational rela xation was not observed during the simulations for either PTMSP or PDMS, an d therefore only thermal fluctuations could redistribute the free volume in both polymers. The higher chain flexibility of PDMS seems to redistribute the free volume more effectively by thermal fluctuation.