CO₂‑Controllable Foaming and Emulsification Properties of the Stearic Acid Soap Systems

Abstract

Fatty acids, as a typical example of stearic acid, are a kind of cheap surfactant and have important applications. The challenging problem of industrial applications is their solubility. Herein, three organic aminesethanolamine (EA), diethanolamine (DEA), and triethanolamine (TEA)were used as counterions to increase the solubility of stearic acid, and the phase behaviors were investigated systematically. The phase diagrams were delineated at 25 and 50 °C, respectively. The phase-transition temperature was measured by differential scanning calorimetry (DSC) measurements, and the microstructures were vesicles and planar sheets observed by cryogenic transmission electron microscopy (cryo-TEM) observations. The apparent viscosity of the samples was determined by rheological characterizations. The values, <i>r</i>_cmc, for the three systems were less than 30 mN·m^–1. Typical samples of bilayers used as foaming agents and emulsifiers were investigated for the foaming and emulsification assays. CO₂ was introduced to change the solubility of stearic acid, inducing the transition of their surface activity and further achieving the goal of defoaming and demulsification