TEXTURES OF SURFACTANT MONOLAYERS

Microscopy studies of coexistence droplets of (tilted) surfactant molecules absorbed at air-water interfaces have demonstrated that such droplets contain a variety of textures. In this paper we describe the observed droplet textures using the Landau free energy for tilted hexatic surfactant films, supplemented by a boundary energy. It is shown that this free energy can naturally explain the morphology of droplet textures with sixfold symmetry. In particular, it predicts (i) the existence of a continuous transition from straight to kinked domain walls and (ii) the appearance of spiral textures associated with spontaneous chiral symmetry breaking in part of the phase diagram. We compare the predicted textures with recent polarized fluorescence and Brewster-angle microscopy experiments.