Cloud and HLB temperatures of mixed-sucrose dodecanoate and poly(oxyethylene) dodecyl ether solutions

Phase behavior of the aqueous system with sucrose fatty acid ester (L-595) and octa(oxyethylene) dodecyl ether (C12EO8) was investigated. The cloud point in the mixed L-595 and C12EO8 system is lower than that of binary water/C12EO8 system at low surfactant concentration whereas the mixed surfactant system shows higher clouding temperature at high surfactant concentration. From the study of the phase behavior in water/L-595/C12EO8 system at 25 °C, surfactant layer curvature of surfactant aggregates formed in the water are changed from highly positive to less positive with the increase in the L-595 content in total surfactant. Therefore, the hydrophilicity of L-595 is lower than C12EO8 at low temperature but higher at high temperature. Cloud temperatures of several mixtures of sucrose fatty acid ester+poly(oxyethylene) dodecyl ether (C12EOn) in water were investigated as a function of the weight ratio of hydrophilic moiety to total surfactant, WH/WS. The cloud temperature is abruptly increased at a constant surfactant concentration with a small change in WH/WS in the mixed hydrophilic sucrose- and lipophilic C12EOn surfactant systems. The slope becomes low in the mixed lipophilic sucrose- and hydrophilic C12EOn surfactant system. In the mixed hydrophilic sucrose- and lipophilic C12EOn surfactant systems, the hydrophilic sucrose surfactant is still hydrophilic even at high temperature. In the mixed lipophilic sucrose- and hydrophilic C12EOn surfactant systems, both sucrose- and C12EOn surfactants become lipophilic at higher temperature since hydrophilic C12EO7 or C12EO8 becomes lipophilic above its own cloud temperature. The similar trends were observed for the HLB temperature in water/mixed surfactant/oil systems. Hence, the phase behavior of combination of hydrophilic sucrose- and lipophilic C12EOn is more temperature-insensitive than that of lipophilic sucrose- and hydrophilic C12EOn.