Liquid Crystals at Interfaces

The ordering in liquid crystals (LCs) can be influenced by an interface. Some of these molecules adsorbed at the air-water interface yield a stable Langmuir monolayer. They exhibit numerous surface phases, which are classified on the basis of intermolecular separation and ordering. These surface phases are governed by the molecular interactions and the ambient experimental conditions such as temperature, humidity, pH, and ion content of the subphase. In this article, the role of molecular interactions on the surface behavior of several rodlike LCs are discussed. The Langmuir monolayer of a cholesteric LC exhibits an interesting low density liquid (L_1′) phase with tilted molecules. Brewster angle microscopy reveals stripe patterns, which arise due to the precession of the tilted molecules. It is demonstrated that this molecular precession can be controlled by the relative humidity, presence of cations in the subphase, and incorporation of appropriate molecular species. The Langmuir monolayer and Langmuir-Blodgett films of a novel rod-disc hybrid LC are discussed.