Thermal transitions of DODAB vesicular dispersions

Two endothermic transitions, at 36 degrees C and 44 degrees C, were observed with differential scanning calorimetry (DSC) upon heating dioctadecyldimethylammonium bromide vesicle dispersions that were equilibrated below 15 degrees C while in samples kept at 25 degrees C there was only the transition at 44 degrees C, which was shown to be the gel to liquid-crystalline transition by H-1-NMR measurements. The transition at 36 degrees C was reversed in an exothermic transition around 13 degrees C upon cooling. The slowness of this transition at ambient temperatures suggests that the presence of the transition at 36 degrees C in a DSC upscan depends strongly on the sample history