Some observations on phase diagrams and structure in binary and ternary systems of didodecyldimethylammonium bromide

Abstract

An account is given of the phase diagrams and structure in both binary and ternary systems formed with didodecyldimethylammonium bromide, dodecane and water. They form L2-phase(microemulsion) and various mesophases very different from ternary amphiphilic systems usually studied. Observations include two lamellar liquid crystalline phases (which can coexist) with very different water contents, of a liquid crystalline hexagonal phase, a highly variable microemulsion structure, a cubic phase with compositions intermediate to those of the L2-phase and the water-rich lamellar phase, and a very stable emulsion. Since the doublechained quaternary ammonium salts are often insoluble in water and oil, they reside at the oil-water interface, and microstructure is therefore much more easily elucidated. This is particularly so if phase behaviour and physical properties adduced from NMR diffusion, conductance and viscosity are combined with recent direct force measurements between bilayers of surfactants adsorbed on mica. The present system, at one end of the spectrum of solution behaviour, forms a well defined entry point to more complicated systems which can be generated by successive perturbations induced by other components.