Rheological investigation of thermal transitions in vesicular dispersion.

The thermal behavior of unsonicated dispersions of a double-chained surfactant, Dioctadecyldimethylammonium bromide (DODAB), has been studied over a wide concentration range using DSC and dynamic rheology. All dispersions are characterized by the pre- and main transition peaks at 35 degrees C and 43 degrees C, respectively. But, only above 10 mM DODAB, a third endotherm at 52 degrees C appears which may correspond to the (ULVs+Lalpha fragments)-->MLVs transition. The thermal-induced MLV's size is proportionally dependent on the concentration. In addition, and in agreement with DSC data, dynamic rheology has proven to be an indirect way to elucidate the structural transitions in these DODAB vesicular dispersions.