Dimethyldioctadecylammonium bromide


Dimethyldioctadecylammonium bromide is a double-chained quaternary ammonium surfactant that forms unilamellar vesicles in water. Among various preparation methods, the ‘‘hot-water” method offers a simple procedure to prepare DODAB cationic vesicles by simply dissolving the DODAB in hot water above 50 °C, i.e., chain melting transition, Tm.
In general, the DSC thermograms of the unsonicated DODAB dispersions are dominated by two endotherms; the pre- and main transition peaks. Moreover, in literature reported the presence of a third
endotherm at 52.2 °C.
The main transition is ascribed to gel to liquid-crystalline phase transition in which the alkyl chains transform from solidlike to liquid-like state.
The 10 mM DODAB is a critical concentration, below which the dispersions consist of large polydispersed unilamellar vesicles that exhibit a local transition at 43 °C, beyond which a structural transition occurs: ULVs --> MLVs as indicated by the sudden increase in the dynamic moduli. However, above 10 mM DODAB, the dispersions are mostly formed by ULVs in coexistence with lamellar fragments resulting in a network that shows a rheogram similar to that of hexagonal liquid-crystalline phase.