Sorption and diffusion behavior of 1,4-diaminoanthraquinone in nylon 6 film.

Abstract

It was found that the values of diffusion coefficient of 1, 4-diaminoanthraquinone (C. I. Dis. Violet 1) in a nylon 6 film, Df, obtained from the concentration-distance profiles at various temperature are greater than the corresponding values obtained from the rate of desorption data by a factor of about 2. In order to clarify the reason for the disagreement in Df, we determined the adsorption isotherms and the concentration profiles of the dye in the film from aqueous solutions at 60, 80 and 90°C. The isotherms and the profiles were analyzed with the aid of a computer. The observed isotherms were not linear but curved, convex to upward, particularly in the range or low dyebath concentration, CS. These isotherms fitted very well to the isotherms calculated by a linear combination of a Nernst type partition and a Langmuir sorption. Therefore, the sorption and diffusion behavior of the dye were explained in terms of the dual sorption model, in which the dye exists in the substrate as the two different species, i.e., the dye adsorbed by the Langmuir sorption (adsorbed species) and that dissolved in the film by the partition mechanism (dissolved species).The analysis of the adsorption isotherms and the profiles on the basis of this model revealed following facts. (1) The concentration of the dissolved species, CP, is normally higher than that of the adsorbed species, CL. However, ratio CL/CP increases with a decrease in the total dye concentration in the film, Cf and with decreasing temperature. (2) The actual diffusivity of the dye in the film, the diffusion coefficient of the dye as a function of Cf, D(C) is not constant but decreases with Cf. This tendency becomes more pronounced at lower temperature. (3) The diffusion coefficient of the dissolved species, DL_??_, is greater than that of the adsorbed species, DP_??_, by a factor of about 2.5 at each temperature. The actual diffusivity of the dissolved species, DP(C), decreases with Cf. While that of the adsorbed species, DL(C), increases with decreasing Cf. The disagreement in the value of Df mentioned above was explained in terms of the dual sorption model.