Volumetric Properties of Surfactant in Water and in Mixed Solvent from Sound Velocity and Density Measurements

Abstract

Abstract A simple, automatic and economic apparatus was constructed for a precise measurement of sound velocity using a resonance method. It gives the sound velocity value with an accuracy of less than 3×10-3% (±2 cm s-1). Sound velocity and density measurements were carried out in aqueous solutions of several compounds of alkyltrimethylammonium bromide (C1TAB, C8TAB, C10TAB, C12TAB, C14TAB, and C16TAB, where Ci is the number of carbons in straight-chain hydrocarbon groups) at 25 °C. Also, the measurements for C12TAB in a mixed solvent with water and 2-propanol were performed. The critical micelle concentrations (CMC) were determined from the inflection point of the compressibility and electric conductivity. The partial molar adiabatic compressibility (κm* ) and the partial molar volume (Vm*) for the surfactant were determined below and above CMC in water and in the mixed solvent from the apparent molar quantities. The partial molar quantities were also found to be dependent on the concentrations of the added alcohol. These results were interpreted from the points of view of the surfactant conditions and solvent structures.