Thermal study of the interaction of crystalline surfactant with water; The dioctadecyldimethylammonium chloride-water system

Dioctadecyldimethylammonium chloride (DOAC) was completely dehydrated under high vacuum and at a temperature above its transition temperature (96.7°C) which was first discovered by us. Thermoanalytical studies on DOAC-water systems indicate that two successive phase changes of coagel → gel and gel → liquid crystal appear due to the increasing structural disorders of polar head groups and hydrocarbon chains, respectively. Furthermore, it is revealed that three types of water exist, i.e., bound, intermediate and free. On the basis of a bilayer-lamellar structure model, a predominant role of the intermediate water in these transitions is pointed out.