Abstract
Pressure effect on the diffusion coefficient D of nine disperse dyes in poly (ethylene terephthalate) (PET) sheet was investigated at 130°C under pressures up to 1kbar by the multiple membrane method. The values of In D showed linear decrease with increasing pressure, giving the activation volume ΔV_??_ for diffusion, 64-123cm3/mol for p-nitroaniline (pNA) and C. I. Disperse Blue 1 (DBl), respectively. The molecular volumes of the penetrants in crystalline state were evaluated from the density measurements, x-ray data and the van der Waals contact models of the molecules. For example, the molecular volumes of pNA and DB1 were 99 and 182 cm3/mol, respectively. The results of ΔV_??_ were now compared with the molecular volumes of the penetrants. It was found that ΔV_??_ increased almost linearly with increasing molecular volume. It was further demonstrated that the anthraquinone derivatives needed larger ΔV_??_ than the azo derivatives compared at the same molecular volume. These as well as the differences between the observed ΔV_??_ and the molecular volumes of the penetrants were discussed from the viewpoint of the free volume theory.
