MICROEMULSIONS OF TRIGLYCERIDE AND NONIONIC SURFACTANT - EFFECT OF TEMPERATURE AND AQUEOUS-PHASE COMPOSITION

The phase behavior of soybean oil, polyoxyethylene (40) sorbitol hexao leate and water-ethanol was investigated. Regions of water-in-oil (W/O ) microemulsions were determined and were found to be strongly depende nt on temperature and water: alcohol ratios. At a water: ethanol ratio of 80/20 (wt.%), an oil: surfactant ratio of 2/3 and a temperature of 25-degrees-C, the microemulsion region extended continuously' from th e oil-surfactant axis to the phase diagram center. However, at the hyd rophilic-lipophilic balance (HLB) temperature (20-22-degrees-C) and a water:ethanol ratio of 80/20 or 75/25 (wt.%), a single-phase area sepa rated from the original microemulsion region. Conductivity measurement s and dynamic light scattering intensities at 25-degrees-C indicated t hat association structures were formed with increasing aqueous phase c oncentrations above 15 wt.%. At 20-degrees-C, the single-phase scatter ing intensities increased sharply with increasing aqueous phase concen trations (38-46 wt.%) and a plateau in the conductivity was detected. Transmission electron microscopy results supported the finding that mo re particles are formed with increasing aqueous phase and form connect ed particles, resulting in constant conductance.