Role of solvent-head-group interaction on the formation of lyotropic liquid-crystals in structured non-aqueous solvents

Molecules of amphiphiles associate in structured solvents to form flexible interfacial films, which may then join up to form crystals. A considerable variety of structures are observed in such crystals. In most cases, consideration of the geometry of the structures, based on frustration analysis, can account for the sequence of phases observed in these systems, independent of the chemical nature of the amphiphilic molecules. The geometric theory is well validated with structured polar solvents whose properties may be either quite similar or quite distinct from those of water. In surfactant-non-aqueous polar solvent systems, only the theoretical phases are in fact observed. However, in water, intermediate phases not accounted for by the geometric theory may be observed. Their conditions of formation are not well understood, indicating that complex phenomena take place in water, a solvent which is nevertheless regarded as an ideal and model solvent. (C) 1997 Published by Elsevier Science B.V.