Kinetic and equilibrium studies associated with the solubilisation of n-pentanol in micellar surfactants

Abstract

Ultrasonic relaxation studies in mixed micellar solutions of the surfactants sodium decylsulphate and dodecyltrimethylammonium bromide with n-pentanol have shown two well defined relaxations associated with the exchange process involving the partitioning of alcohol and also surfactant monomer with the mixed micelle. The monomer concentration of n-pentanol has been measured using head-space analysis involving gas chromatography, and the surfactant monomer concentrations have been determined from specially fabricated surfactant-selective electrodes. The combined relaxation/equilibrium data have been analysed using a phenomenological treatment in which the kinetics and thermodynamics associated with both exchange processes have been evaluated. The main conclusion from this work is that the association of both alcohol and surfactant monomer to the mixed micelle is almost a diffusion-controlled process and that the aggregation numbers of the mixed micelles apparently decrease when alcohol is added.