(84g) Multicomponent Diffusion in Aqueous Nonionic Micellar Solutions with Decane

When a hydrophobic solute, such as a drug or nutrient, diffuses in the presence of micelles or surfactant aggregates, the partitioning of solute into the oily interior of the aggregates strongly affects the rate of diffusion of both the solute and the surfactant. In this work, the effect of decane on the ternary diffusivity matrix and the micelle diffusion coefficient in aqueous solutions of nonionic surfactant (C₁₂E₁₀) has been investigated with Taylor dispersion and dynamic light scattering (DLS) techniques. Here, surfactant and decane diffuse together exclusively as decane-containing micelles. Thus, one might expect both surfactant and decane to diffuse with the micelle diffusion coefficient, and the Taylor dispersion results show that surfactant does indeed diffuse down the surfactant gradient according to the micelle diffusion coefficient. However, decane is observed to diffuse down a decane gradient with a diffusivity that is four times smaller than the micelle diffusion coefficient. An existing predictive model that requires knowledge of the micelle size, shape, interaction potential and aggregation number, all acquired from DLS data, has been used in an attempt to understand why the rate of hydrophobic solute transport is dramatically reduced in micellar solutions.