Determining Diffusion and Convective Mass Transfer Coefficients in Dyeing a Thin Flat Film

Abstract

A method based on laser scanning confocal microscopy (LSCM) has been developed for simultaneously obtaining the diffusion coefficient D and the ratio of the convection mass transfer coefficient h_m and the partition coefficient K. This new method, which is demonstrated for a nylon film dyed with a disperse dye, is nondestructive and much faster than previously used methods for obtaining D that neglect the boundary layer effects. Although based on the fluorescence of dyes, this technique is successfully used with real dyes (not model dyes) at industrially relevant concentrations. LSCM is used to quantita tively measure the relative concentration profiles of a dye through a film, and corrections are made for the strong absorption of the incident laser light as it passes through the film. The data are then modeled using known mass transfer relationships to simultaneously obtain D and the ratio h_m/K. Since K is measured in a separate experiment, all three mass transfer parameters are determined.

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