ABSTRACT
The thermodynamic and molecular motional states of water and surfactant, and their thermal transitions, were examined in several surfactant/water lyotropic liquid crystals by DSC, isopiestic vapor pressure, FTIR, and 1H-NMR spectroscopy. The presence of the three types of water at room temperature was corroborated by FTIR spectroscopy. Many surfactant/water lamellar liquid crystals exhibit a gel-to-liquid crystal transition. The instrument was calibrated with indium, water and n-octane standards. Surfactants frequently form lyotropic liquid crystalline phases by incorporating in their structures considerable amounts of water and/or organic solvents. Bulk water molecules, in turn, have stronger intermolecular hydrogen bonding, leading to clusters of water molecules that further shift the band frequency to the lower side of the spectrum. The melting enthalpy of water decreases linearly with Brij 58 concentration and becomes zero at about 68 wt%. At this concentration, there are ca. 29 water molecules per molecule of Brij 58, or 1.4 water molecules per ethylene oxide group.
