Effects of added urea and alkylureas on gel to liquid-crystal transitions in DOAB vesicles

The gel to liquid-crystal transition for vesicles in aqueous solution formed by dimethyldi-n-octadecylammonium bromide (DOAB) occurs at 44.7 degrees C. Moreover, the shapes of the scans recorded by a sensitive DSC microcalorimeter are very similar when the vesicular solutions are prepared starting with solid DOAB and comparable amounts of either solid urea or solid alkylureas. Therefore, the DOAB vesicles in aqueous solution accommodate this class of solutes without marked changes in the melting temperature and the enthalpy of the transition. The contrast with effects of added surfactants and simple organic solutes such as THF and ethanol is particularly significant.