Phase behavior and microstructure of nonaqueous microemulsions

Phase behavior of glycerol, propylene glycol, hydrocarbon, and alkylpolyglycol ether (C_iE_j) surfactant microemulsions has been studied. Surfactant solubility in the polar organic phase (a mixture of glycerol and propylene glycol) decreases when glycerol content is increased, and a 2-3-2 phase transition is observed at constant temperature. The phase behavior usually observed in water microemulsions as a function of temperature is observed here as a function of the fraction of glycerol in the polar organic phase. Phase behavior is reported as a function of oil solvophobicity and the surfactant solvophilic-lipophilic balance and is compared to a well-established model developed for aqueous microemulsions. Porod analysis of small-angle X-ray scattering (SAXS) measurements indicates the presence of interfaces; thus the fluids are microstructured. The SAXS measurements suggest that aqueous and nonaqueous microemulsions are structurally similar.