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 Nernsttype 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 decreasing 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 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. Dye diffusion on fibers is closely related to the rate of dyeing, level dyeing through dye migration, wet fastness properties of dyes, and so on. Therefore, the diffusion behaviors of dyes in various polymers have been extensively studied [3,5,9,11,21 ].Sorption and diffusion mechanisms of disperse dyes in hydrophobic fibers from water have been characterized in terms of Nemst-type partitioning [9] and ideal Fickian diffusion [3,9], respectively. 7fiat is, dyes dissolved in water are linearly distributed between water and fibers up to the saturation limit of dyes in water, and dye diffusivity on polymers is independent of dye concentration Cf on polymers [7, 10]. mer taken up by the partition mechanism at equilibrium and that by Langmuir sorption, respectively, and Kp is the partition ooefficient.We also found that for the diffusion of nonionic dyes (model disperse dyes) on nylon 6 61m, the actual diffusivity D(c,~, that is, the di8usivity of the dye on the polymer as a function of cp decreases with decreasing Cp particulariy in the range of low C/t!3, 161.According to the dual-mode sorption model dye penetrates polymer as two distinct qxxim i.e., dye taken up by Nernst-type partitioning (P species) andat University of Sussex Library on February 9, 2015 trj.sagepub.com Downloaded from
