Temperature and composition effects on the morphology of o/w dispersions based on poly(oxyethylene 20) sorbitan monolaurate and sorbitan monolaurate

Phase behavior of colloidal systems containing oleic acid, poly(oxyethylene 20) sorbitan monolaurate, sorbitan monolaurate, and water were studied as a function of composition and temperature. The pseudo-ternary diagram of the resultant dispersions showed the presence of regions related to the occurrence of microemulsions, gel microemulsions, high viscosity emulsions, and low viscosity emulsions. SAXS indicated that compositions with surfactant contents above 50% presented lamellar structures. The same technique was used to detect that this structure was destroyed at 45 degrees C for systems with oleic acid contents of 10%, while dispersions with 1.5, 2, and 5% of oleic acid did not have their lamellar structure disrupted at this temperature. It indicated that, at the highest oleic acid content used in this work, non-ionic surfactants tended to interact with each other, destroying lamellar structure and promoting cloud point-related phenomena, as indicated by turbidimetry and DLS.