ABSTRACT
Liquid crystals (LCs) are self-assembled organized mesophases with properties intermediate to those of crystalline solids and isotropic liquids [1]. In LC phases, long-range periodicity exists, although the molecules exhibit a dynamic disorder at atomic distances, as is the case in liquids. Accordingly, these materials can also be considered as ordered uids [2]. Lyotropic LCs (LLCs) are materials that are composed from at least two molecules: an amphiphilic molecule and its solvent. A hydrophilic solvent, such as water, hydrates the polar moieties of the amphiphiles via hydrogen bonding, whereas the exible aliphatic tails of the amphiphiles aggregate into fused hydrophobic regions based on van der Waals interactions. In addition to morphological dependence on the chemical composition, LLCs are also sensitive to external parameters, such as temperature and pressure [1-3]. As a function of the molecular shape of the surfactants, packing parameters, and interfacial curvature energy considerations, LLCs can be formed with aqueous domains ranging from planar bilayer lamellae to extended, cylindrical channels, to three-dimensional (3-D) interconnected channels and manifolds [4]. These mesophases are dened as lamellar (Lα), hexagonal (H), bicontinuous cubic (Q [or V]), and discontinuous cubic (I) phases, based on their symmetry [5]. In addition, most lyotropic mesophases exist as symmetrical pairs, a “normal” (type I) oil-in-water system, consisting of lipid aggregates in a continuous water matrix, and a topologically “inverted” (type II) water-inoil version. The headgroups hydrated by water are arranged within a continuous nonpolar matrix, which is composed of the uid hydrocarbon chains [5]. In addition to its biological signicance, inverse lipid phases could be useful as host systems for the incorporation of food additives [6,7], the crystallization of membrane proteins for drug delivery [7,8], and for inorganic synthesis [9].
