Thermotropic mesomorphism has been observed in pure compounds consisting of simple disc-like molecules, viz., benzene-hexa-n-alkanoates. Thermodynamic, optical and x-ray studies indicate that the mesophase is a highly ordered lamellar type of liquid crystal. Based on the x-ray data, a structure is proposed in which the discs are stacked one on top of the other in columns that constitute a hexagonal arrangement, but the spacing between the discs in each column is irregular. Thus the structure has translational periodicity in two dimensions and liquid-like disorder in the third.

Some fatty acids, lipids, polymers and mesogenic molecules which are amphiphilic in nature spread at the air-water interface to form stable Langmuir monolayers. They exhibit a rich variety of two-dimensional (2D) phases. In this article, we briefly review some of the novel features we have found in these monolayers. For example, we find transition from a 2D monolayer to three-dimensional structures possessing liquid crystalline order, induced liquid condensed phase, demixing of liquid expanded phase, critical points and pattern formation.