Influence of n-butanol on the size of sodium dodecyl sulfate micelles

Abstract

Surfactant tracer diffusion coefficients have been measured for aqueous micellar solutions of sodium dodecyl sulfate (SDS) in the presence of added medium chain alcohol. The alcohol used in the experiments was n-butanol (with a range of concentrations of 0-0.162 M), and surfactant diffusion was measured as a function of alcohol concentration. The results showed that surfactant tracer diffusion coefficients (which we take to be a weighted average of monomer and micellar forms) were largely invariant with respect to alcohol concentration. From these data, the effect of added n-butanol on micellar diffusion coefficients was calculated. This was done by fitting data (K. Hayase and S. Hayano, Bull. Chem. Soc. Japan 50, 83 (1977)) for the critical micelle concentration (CMC) decrease, as well as our own results in terms of n-butanol concentration. The calculated diffusion coefficients for SDS micelles were also found to be practically invariant with addition of n-butanol over the concentration range given above. This study suggests that changes in micelle size (reflected by the micellar diffusion coefficients) for the system examined here does not depend on alcohol concentration.