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Ultrasonic measurements were made on terbium laurate and myristate in 60/40 benzene-methanol mixture (v/v), to determine the critical micellar concentration (CMC), ultrasonic velocity and other acoustic parameters. The results confirm that there is a significant interaction between the soap and solvent molecules. The critical micellar concentration and thermodynamic parameters for dissociation and micellization process for terbium laurate and myristate in a mixture of 60/40 benzene-methanol (v/v) at different temperature were evaluated from conductivity measurements. The results showed that these soaps behave as weak electrolytes in dilute solutions.

Density, viscosity, ultrasonic velocity and refractive index measurements of Glycerol Monostearate (GMS) in 80/20 (% v/v) benzene-methanol mixture at 290 K with varying concentrations have shown that there is noticeable variation in aggregation of non-ionic surfactant at Critical Micellar Concentration (CMC). Density and viscosity results have been satisfactorily explained by some well-known equations viz. Jones-Dole, Moulik, Vand, Einstein and Root. Jacobson model has been used to evaluate adiabatic compressibility, molar compressibility, solvation number molar sound velocity, relaxation strength, relative association and other allied acoustical constants. The variation of refractive index with concentration of GMS solutions shows a marked change in value at CMC. Treatment of data obtained from density, viscosity, ultrasonic velocity and refractive index measurements has shown that strong interaction exists between GMS and solvent molecules, and GMS molecules do not aggregate considerably in pre-micellization region.

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