Formation of vesicular bilayers in aqueous solutions containing mixtures of dialkyldimethylammonium bromides

DSC scans for vesicles in aqueous systems produced by mixtures of dihexadecyldimethylammonium (DHAB where R = C16H33 in R2N+Me2Br-) and dioctadecyldimethylammonium bromides (DOAB where R = C18H37 in R2N+Me2B-) show for most mixtures two melting points corresponding to gel to liquid-crystal transitions which depend on the composition of the vesicular system. The gel to liquid-crystal transitions occur over a wider temperature range than for vesicular systems prepared using a single dialkyldimethylammonium surfactant. The resulting temperature-mole fraction diagram is similar to that observed for continuous solid solutions. The overall pattern shows that in a given solution two types of domains in the vesicular bilayer systems can co-exist having slightly different compositions and hence melting temperatures. (C) 1998 Elsevier Science B.V.