BROWNIAN-MOTION OF LIPID DOMAINS IN ELECTROSTATIC TRAPS IN MONOLAYERS

Fluorescence microscopy can be used to visualize lipid monolayers at the air-water interface. These monolayers frequently show coexisting lipid phases, with a rich variety of domain shapes. The sizes, shapes, and shape transitions of isotropic domains can be accounted for phenomenologically in terms of a competition between an interphase line tension, lambda, and mu-2, the square of the difference in the dipole densities in neighboring domains. Theoretically, domain sizes, shapes, and shape transitions all depend on the ratio lambda/mu-2. In the present work it is shown that mu-2 can be determined from an analysis of the amplitude of Brownian motion of lipid domains. By combining measurements of the equilibrium sizes and shapes of domains, and Brownian motion, one can in principle determine both lambda and mu-2 in lipid monolayers.