THE STATE OF WATER IN LYOTROPIC LIQUID-CRYSTALS

Several surfactant-water systems were studied by means of differential scanning calorimetry (DSC) and polarizing microscopy. The surfactants studied were sodium dioctylphosphinate (SDOP), didodecyldimethylammonium bromide (DDAB), dioctadecyldimethylammonium bromide (DODAB), n-decanephosphonic acid (DPA), n-dodecanepbosphonic acid (LPA), Brij 35 and Brij 58. Depending upon the nature of the surfactant, up to four different types of water were found, differing from one another in their melting and freezing temperatures. Some water was undetectable by DSC: two water molecules per surfactant molecule in SDOP, DDAB and DODAB, and 1.40 water molecules per oxygen atom in Brij 35 and Brij 58. Up to two different types of ''interfacial'' water may exist, with different melting and freezing points: 9.6 water molecules per surfactant molecule in SDOP and 3.07 water molecules per oxygen atom in Brij 35 and Brij 58. All other water in each system behaved as pure (''free'') water.