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

Abstract

Diffusion of light gases in poly[1-(trimethylsilyl)-1-propyne] (PTMSP) and poly(dimethylsiloxane) (PDMS) was investigated by a molecular dynamics technique. Diffusion coefficients of helium and neon in PTMSP were larger than those in PDMS due to the larger free volume fraction of PTMSP in spite of its higher chain rigidity. This indicates that the amount of the free volume fraction is a more important factor than the redistribution of the free volume for the diffusion of light gases in either polymer. Conformational relaxation was not observed during the simulations for either PTMSP or PDMS, and 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.