ABSTRACT
Liquid crystalline systems formed by cationic surfactants have been described in numerous publications. The structural characteristics of liquid crystalline mesophases, the arrangement of the molecules, and the globular, cylindrical, or lamellar structure of the associations have been revealed by analysis of the phase diagrams of surfactant/cosurfactant/water systems by Ekwall et al. [1] and Friberg and coworkers [2,3]. Hoffmann [4] has analyzed the micelles formed by cationic and anionic surfactants in solutions of various concentrations and has studied the properties of the different phases formed by rheological and X-ray diffraction methods. Friberg and Venable [3] studied tetradecyltrimethylammonium bromide/pentanol/water systems and established that the interlamellar distance was dependent on the water/ surfactant ratio but the presence of the cosurfactant also affected (reduced) the extent of swelling of the liquid crystalline system. As for cationic surfactants, hexadecylpyridinium chloride/alcohol/benzene/water quaternary systems were studied by Dékány et al. [5] using X-ray diffraction methods. It was shown that water was incorporated into the organic (benzene, cyclohexane, alcohol) inverse liquid crystalline mesophase of the lamellar structure and caused interlamellar swelling. The interlamellar distance can be manipulated not only by adjustment of the water/surfactant ratio but also by the addition of alcohols acting as cosurfactants [5]. Lamellar liquid crystalline systems are also suitable for the preparation and stabilization of nanoparticles. Nanoparticles are incorporated between the bilayer membranes and are thereby stabilized, as verified by small-angle X-ray scattering (SAXS) measurements [6,7]. Wang et al. [8] studied systems composed of silver hydrosol or organosol and lamellar sodium dodecyl sulfate (SDS)/hexanol/ dodecane/water. Depending on the hydrophilic or hydrophobic character of the silver nanoparticle, it was incorporated into the aqueous or organic portion, respectively, of the lamellar bilayer phase and a stable dispersion was formed [8].
