AMPHITROPIC LIQUID-CRYSTALS .1. EFFECT OF A THERMOTROPIC MESOGEN ON LYOTROPIC MESOMORPHISM, AND OF A SURFACTANT ON THERMOTROPIC MESOMORPHIM - THE C16EO8-5-CB-WATER SYSTEM

The mesomorphic properties of a ternary system consisting of a thermotropic mesogen (pentylcyanobiphenyl; 5-CB) and a lyotropic system (octaethyleneglycol hexadecyl ether-water; C16EO8-H2O i.e. 3,6,9,12,15,18,21,24,-octaoxatetracontan-1-ol) have been studied using optical microscopy, differential scanning calorimetry, nuclear magnetic resonance spectroscopy and low-angle X-ray diffraction. The two types of mesophase are immiscible. Addition of the surfactant to 5-CB reduces the nematic-isotropic transition, until above ca. 30 wt.% no nematic phase is observed. Similar results were observed with other polyoxyethylene surfactants. The surfactant, C16EO8, forms a large range of lyotropic mesophases (lamellar, hexagonal, two types of cubic and nematic). Up to 12% 5-CB was solubilised in the lamellar phase, whilst only ca. 5% dissolved in the hexagonal phase and lower concentrations still could be incorporated into the other mesophases. X-Ray and (H2O)-H-2 NMR measurements indicate that 5-CB swells the alkyl-chain region of the surfactant, rather than adsorbing at the headgroup-water surface.