Similarities of aqueous and nonaqueous microemulsions.

The phase behavior of ternary mixtures of water, hydrocarbons, and nonionic amphiphiles is, by now, well known. In this paper the effect of replacing water by formamide is studied. This polar protic solvent reduces the hydrophobic effect and, thereby, the repulsive interactions with surfactant tails. The result is a higher mutual solubility of formamide and surfactant, a weaker adsorption at the internal interface and, hence, a lower solubilization capacity of the amphiphile. The reduced amphilphilic strength of surfactants in formamide corresponds to Ci-4E in aqueous systems. As with aqueous systems the present mixtures form microstructures, namely oil-droplets in formamide and formaide-droplets in oil. For equal volumes of formamide and oil, small-angle neutron scattering (SANS) spectra indicate the existence of bicontinuous structures. [ABSTRACT FROM AUTHOR]