DIFFUSION COEFFICIENT OF DYE IN A POLYMER USING MULTIPLE-SHEET ARRANGEMENTS WITH A STEP PROFILE OF THE INITIAL CONCENTRATION

A method to obtain the diffusion coefficient D of a diffusant in a polymer substrate is described. It basically applies the multiple-sheets, in which an amount α of the diffusant was initially distributed within the central sheet, giving a concentration distribution of a step function. After a diffusion interval t, the broadened concentration distribution across the stacked sheets, C(x, t), was determined spectroscopically and analysed by the following equation. D was calculated from the slope of ln C vs. x2/4t plots. The applicability of this method was demonstrated for the diffusion of p-aminoazobenzene into a nylon 6 sheet at 90°C where the diffusion interval, the thickness of the polymer sheet and the initial concentration of the diffusant in the central sheet were varied. In contrast to experimental setups where diffusion of a dye into a polymer is measured in the presence of solution of the dye, the described method yields diffusion coefficients of dyes in polymers which are not influenced by the simultaneous diffusion of the solvent.