Formation of Microemulsions with Gemini-Type Surfactant

Abstract

Disodium N,N’-dilauroylethylenediamine-N,N’-disuccinate (gemini surfactant, GS) and sodium N-lauroyl-N-methylamine succinate (monomeric surfactant, MS) form middle-phase microemulsions at an optimum mixing ratio with glycerol mono(2-ethylhexyl)ether (MEH) as a cosurfactant in the presence of NaCl. The solubilization capacity of microemulsion in the GS system is about twice as much as that of microemulsion in the MS system. This difference in solubilization capacity may be attributed to tight packing of GS molecules at a micro water-oil interface inside the microemulsion. With decreasing the salt content in water, the three-phase region consisting of excess water, oil phases and a middle-phase microemulsion shrinks and finally disappears, perhaps, at a tricritical point, at which three phases become simultaneously identical. The temperature dependence on the phase behavior of the microemulsions is also reported.