AbstractThe diffusion coefficient at zero concentration and the free volume parameters in Fujita's free volume theory were measured for benzene, hexane, and heptane in modified polyethylene films using an unsteady‐state absorption technique. Films were modified by gamma irradiation, solvent conditioning, and post‐ and preirradiation conditioning.Dc=0was found to drop with irradiation, the drop being larger the larger the molecular size of the diffusing molecule. A relationship for the dependance ofDc=0on the crosslink density is proposed. Solvent conditioning led to an increase inDc=0directly proportional to the swelling power of the conditioning agent and to the molecular size of the diffusant molecule. In most cases, combined treatment resulted in an increase inDc=0, the extent of which was dependent upon the relative effect of the swellant and the irradiation dose. In all cases, postirradiation conditioning led to values ofDc=0higher than those obtained by preirradiation conditioning. The fractional free volume of the polymer was found to decrease with irradiation, showing a marked drop at low doses when reaching a state where the dose was of small effect. Changes inf(0,T) with conditioning and with combined treatment followed the same general pattern asDc=0. β(T) was unaffected by any kind of treatment studied.Bdchanged in practically the same manner asf(0,T) but in the opposite direction. A method is proposed for the optimum choice of a membrane modification procedure based on solubility and diffusivity res
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