Model for chemical interdiffusion of solubilizates and ionic micelles. Aqueous solutions of n-alcohols and sodium dodecylsulfate

Abstract

A Taylor dispersion tube has been used to measure ternary interdiffusion (mutual diffusion) coefficients for sodium dodecylsulfate(NaDS)–n-hexanol–water and NaDS–n-octanol–water aqueous solutions. The measured diffusion coefficients give the fluxes of total NaDS and total alcohol components, including cross-coefficients for the coupled flux of NaDS caused by the concentration gradient in alcohol and vice versa. Hexanol and especially octanol are extensively solubilized in NaDS micelles. The diffusion of the solubilized portion of each alcohol was expected to cotransport large amounts of NaDS. Yet diffusing octanol produces large countercurrent coupled flows of NaDS. To help understand the results, Nernst–Planck equations are used to develop a model for the interdiffusion of solubilizates and ionic micelles. The model includes changes in the extent of counterion binding caused by solubilization and coupled transport of solubilizate driven by the electric field which is generated by the diffusion of the charged micelles and mobile counterions.