Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, Vol.333, 69-78, 1999
The effect of the cholesteric structure on the water activity of lyotropic liquid crystals
The study of the water activity behavior on liquid crystals is reported for lyomesophases based on sodium dodecylsulphate (SLS), decylammonium chloride (CDA) and potassium laurate (LK). Different amounts of chiral solutes (sugars or cholesterol) were added to the nematic matrices in order to form the helical structure characteristic of the cholesteric system. The water activities of all mesophases were measured in order to evaluate how the water availability of lyomesomorphic systems is affected by the formation of the helical structure. It was verified that the helix formation on CDA system leads to a decrease of the intermicellar forces driving to a situation where the water is less tightly bound, Seemingly, after an initial cholesterization, the micelle-solvent interaction increases with the cholesterol concentration. For systems based on SLS the formation of the helical structure leads to a condition where the water molecules are more tightly bound and, after an initial cholesterization, the micelle-solvent interaction does not change with the further addition of inductor. For the LK systems it could be observed that a decrease of the water activity occurs only when hydrophilic inductors are added. LK systems present a rate of loss of water significantly larger than the CDA.
Keywords:water activity;liquid crystals;lyotropic liquid crystals;organized systems;water vapor pressure