Highly water dilutable green microemulsions

The realms of existence of “green” microemulsions are reported and their pseudo-ternary phase diagrams as well as electrical conductivities. For the investigations, the model system water/sodium oleate/citronellol/limonene is used. Herein, sodium oleate is the surfactant and citronellol the cosurfactant. The optimal surfactant-to-cosurfactant mass ratio is found to be 1:1. By replacing successively citronellol with ethanol the homogeneous single phase can be extended. At first, an anti-percolative behaviour of the system is obtained that can be converted into a percolative one. For low ethanol content microemulsions remain of water-in-oil (w/o) type. With increasing ethanol, between 30 and 90 wt% of ethanol in the blend, the monophasic region is diminished whereas liquid crystalline phases (lamellar and mixed lamellar and cubic ones) extend in the water-rich area. Above 90% the realms of existence of microemulsions are increased again and bicontinuous structures and oil-in-water (o/w) microemulsions were found. For a certain percentage of ethanol (92.5%) in the blend with citronellol and a surfactant + cosurfactant-to-oil ratio equal to or higher than 4:1 a highly water dilutable concentrated microemulsion is formed which can incorporate 99 wt% of water. By adding water rapidly to the water-rich areas of this system, thermodynamically unstable translucid nanoemulsions can occur, which turn into transparent microemulsions with time.