Langmuir Monolayers and Liquid Crystals

Abstract

Over the past ten years, intensive studies of insoluble monolayers at the air/water interface (Langmuir monolayers) has revealed that there are close connections between the order in such films and that in smectic liquid crystals. By combining grazing incidence diffraction and imaging methods such as Brewster-angle microscopy, it has been shown that there are one-to-one correspondences between monolayer and liquid crystal phases. Monolayers have also been shown to have optical textures similar to those in smectics. The textures, which arise from an ordering of the molecular tilt azimuth, can be understood in terms of a Landau-de Gennes theory that is modified to take into account the broken symmetry at the interface. The tilt organization is most striking in ordered domains of a condensed phase surrounded by an isotropic phase. In such cases there is a coupling between the order within a domain and its shape, which has also been addressed by theory.

Key Words:

• Langmuir monolayers
• textures
• phase diagrams
• smectic liquid crystals
• hexatic phases
• tilt order