THERMAL TRANSITIONS IN SURFACTANT-BASED LYOTROPIC LIQUID-CRYSTALS

The state of water and several thermal transitions were examined in several surfactant/water lyotropic liquid crystalline systems. The surfactants studied were Aerosol OT (AOT), didodecyldimethylammonium bromide (DDAB), dioctadecyldimethylammonium bromide (DODAB) and n-decylphosphonic acid (DPA). In the AOT/water system, three types of water were detected: ''bulk-like'' water, interfacial water and hydration water (about six molecules of water per molecule of AOT). This system does not exhibit the gel-liquid-crystal transition, probably because the branched, short tails of AOT do not allow for crystallization upon cooling because of steric hindrance. In the DDAB/water and DODAB/water systems, only bulk-like water and two molecules of hydration water per molecule of surfactant were observed. The gel-liquid-crystal transition was detected at 15-degrees-C for DDAB and at 50-degrees-C for DODAB. In the DPA/water system, only bulk-like water was seen. The gel-liquid-crystal transition for this surfactant was detected at about 12-degrees-C.