THE DIFFUSION MECHANISM IN SILICONE-RUBBER

The significance of permeant-polymer interactions to the diffusion process in silicone rubber is explored. A simple expression for the diffusion coefficient is derived based on adsorption events occurring throughout the volume of the polymer, and tested with apparent success against previously published data. A concentration-dependent diffusion coefficient is then derived based on the formation of a Langmuir-type adsorbed layer that effectively covers and hence neutralises strong permeant-polymer interaction sites throughout the polymer volume. This diffusion coefficient is used to numerically generate permeation transients which are compared with experimental data for the case of 1-aminobutane permeation through silicone rubber. It is shown that differences between these two sets of data can be significantly removed if it is assumed that permeant dwell times at strong adsorption sites within the polymer decrease as the fractional occupation of these sites increases.