Effects of pressure and solvent on the diffusion of aromatic compounds through polymers

The diffusion of six azo and five anthraquinone derivatives through nylon 6, poly(ethylene terephthalate) and secondary cellulose acetate films were studied under high hydrostatic pressures of up to 3000 bar and at temperatures 80–130 °C, by analyzing the diffusion profiles yielded in a stacked multiple film, placed in the solution of the diffusant. It was found that the diffusion coefficient,D, of the diffusant decreased with increasing pressure, giving a linear relationship between InD and the pressure, the slope of which gave the activation volume for the diffusion,V. It was revealedV increased linearly with increasing intrinsic molecular volume of the diffusant,V_w, the slopes being different between the azo and the anthraquinone derivatives. The ratio ofV toV_w (V/V_w) ranged from 0.13 to 0.93, depending in a sensitive manner on the degree of swelling of the polymer matrix which in turn was varied by the solvent. The overall results could be explained in accordance with the formulation,V_{f, local} +V=V_w, whereV_{f, local} represents the free volume contribution. It was proposed thatV_w is increased by solvation when the solvent is good for the diffusant.