Diffusion of disperse dyes on nylon 6

The diffusion behavior of nine azo and two anthraquinone dyes on nylon 6 him is studied by analyzing dye distribution profiles. Relations between concentrations C-f of dyes on the film and the actual diffusivities D-(C) of the dyes (C-f - D-(C) relation) are determined from the profiles using Matano's method. For most dyes, C-f - D-(C) relations at 80-90 degrees C are explained well in terms of the dual-mode sorption-diffusion model in which the dye penetrates the polymer as two distinct species: dye taken up by Nernst-type partitioning (P species) and by Langmuir sorption with one class of sorption site (L species). The actual diffusivity DP(C), of the P species decreases gradually with decreasing C-f, from C-f at the polymer surface (C-fsur) to C-f corresponding two to three times the saturation value of Langmuir sorption (S). Below this C-f, D(CP) decreases rapidly with decreasing C-f. Actual diffusivity D-L(C) of the L species usually increases gradually with decreasing C-f. As a result, D-(C) values of disperse dyes are almost constant or gradually increase(or decrease) with decreasing C-f, from C-fsur to C-f corresponding to two to three times S, and then decrease rapidly with decreasing C-f. For diffusion of some dyes at low temperatures (<60 degrees C), the C-f-D-(C) relations may be explained much more accurately by considering that all three sorption modes operate concurrently, i.e., Nernst-type partitioning and two classes of Langmuir sorption, one with high affinity and small S, and other with low affinity and large S.