Concentration Dependence of the Diffusion Coefficients of Disperse Dyes in Polyethylene Terephthalate

Diffusion coefficients of disperse dyes have been calculated by Matano's method from diffusion profiles in polyethylene terephthalate(PET). The diffusion coefficients (Dc) clearly indicate concentration‐dependence. It has been found, from the densities of the dyed PET and the dye, that there is no overall change in the volume of the PET and dye in dyeing. The instrinsic diffusion coefficients have been calculated from Dc and the volume fraction (φ1) of penetrant in the amorphous region. From these values, thermodynamic diffusion coefficients (χẗ) were obtained. It has been found that the relation between 1/log (χẗ/χo) and 1/φ1 is a straight line, and it therefore seems reasonable to assume that the diffusion of disperse dyes in PET can be described by Fujita's ‘free volume theory’ for the diffusion of low molecular‐weight organic compounds in an amorphous high‐polymer.