Diffusion of Disperse Dyes on Nylon 6

The diffusion behavior of nine azo and two anthraquinone dyes on nylon 6 film 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°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 D P ( C ) of the P species decreases gradually with de creasing C f , from Cf at the polymer surface ( C fsur ) to Cf corresponding two to three times the saturation value of Langmuir sorption ( S). Below this C f , D ( C ) P decreases rapidly with decreasing C f . Actual diffusivity D L(C) of the L species usually increases gradually with decreasing Cf. As a result, D ( C ) values of disperse dyes are almost constant or gradually increase (or decrease) with decreasing Cf, 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°C), the C f - D ( C ) relations may be explained much more accurately by considering that all three sorption modes operate concur rently, 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.