The shapes of domains in two-phase monolayer systems

The kinetics of phase transitions in two dimensions can be examined experimentally in monolayers at the air/water interface. Some investigations of transitions between isotropic monolayer phases have been already carried out. But many of the phases in monolayers of simple amphiphiles are mesophases in which there are textures that are related to the molecular order, much the same as the textures in liquid crystals, and this structure will affect the morphology of evolving phases. The shapes of domains of mesoscopically ordered phases surrounded by an isotropic phase represent a balance between electrostatic fortes, the order parameters: that control the texture and the boundary conditions at the edge of the domain. Bubbles of an isotropic phase surrounded by an ordered phase also reflect this competition. The texture and shape are closely coupled and there is a marked dependence on domain or bubble size. Measurements of the shapes of bubbles and domains by Brewster-angle microscopy and by scanning force microscopy on films transferred to solid substrates are described and compared with a recent continuum elastic model.