Application of Acoustic Spectroscopy to the Characterization of Surfactant Solutions, Emulsions, and Microemulsions: d–Limonene–Water–C₁₂EO₇–Isopropanol System

Abstract

The application of acoustic spectroscopy to the characterization of binary C12EO7—water system was studied. It was discovered that the size of micelles in aqueous surfactant solutions could not be determined, but it was possible to determine the size of water nanodomains existing in the surfactant‐rich systems. It was suggested that in colloidal systems, the energy of ultrasonic waves is dissipated only by interfaces existing between condensed phases. The characterization of Winsor transitions by acoustic spectroscopy in water/d‐limonene system stabilized by a mixture of nonionic surfactant and isopropyl alcohol (cosolvent) was also explored. In one study, systems with a constant d‐limonene to water weight ratio obtained in the course of titration of d‐limonene‐in‐water emulsion with increasing amounts of surfactant+alcohol were investigated. In another study, a balanced d‐limonene/water microemulsion was sequentially diluted with water and d‐limonene. The transition between Winsor I and Winsor IV systems was monitored in both cases. Droplet size distributions were calculated using different models for dispersed and continuous phase composition. It was demonstrated that the magnitude of acoustic scattering played a significant role in the ability to reliably determine droplet size distributions, and in particular to simultaneously observe nanometer‐size and micron‐size droplets in Winsor I systems. An attempt was made to account for intrinsic attenuation of surfactant and alcohol by associating them with the aqueous phase, but this approach was shown not to be applicable in the case of Winsor IV microemulsions.