Ultrasonic relaxation studies on micelle formation in aqueous solutions of some bile salts

Abstract

Ultrasonic relaxation studies have been carried out in aqueous solutions of biological surfactants namely bile salts (sodium cholate and sodium deoxy cholate) at 303.15K in the concentration range 1 to 14mM and in the frequency range 2–30MHz. The ultrasonic velocity is determined at 2MHz using a Digital Ultrasonic velocity meter. The ultrasonic absorption is measured in the frequency range 2–30MHz using Fallen Instruments and Pulsed Power Oscillator systems. The variation in the ultrasonic absorption is explained on the basis of exchange of a surfactant monomer between the micelles and the surrounding bulk solution. An attempt has also been made to extend the application of Aniansson and Wall and Teubner models to explain the micellar kinetics of biological surfactants which is otherwise applied to explain the kinetics of ordinary surfactants only. Various kinetic parameters such as associative rate constant (k+1), dissociative rate constant (k−1) and the volume change (∆V) for the monomer–micelle exchange are estimated and reported in this paper.