QUANTIZED SYMMETRY OF LIQUID MONOLAYER DOMAINS

Theoretical arguments have been developed that the shapes of lipid domains at the air-water interface can be understood in terms of a competition between line tension and long-range electrostatic forces. These electrostatic forces can be approximated by effective dipoles, that is, the differences in dipole densities mu in coexisting phases. Recent experimental work has given quantitative confirmation that the long-range electrostatic forces can be expressed in terms of these dipoles. The present work further tests the theory of domain shapes involving competition between line tension and dipolar forces by observations of transitions of circular domains to domains of lower symmetry. These transitions occur when the electrostatic repulsive forces exceed the forces of line tension lambda. Transitions of circular domains to domains with shapes of lower symmetry are functions of domain radius and the dimensionless parameter lambda/mu2; the experimental results are in accord with theory to within the experimental error.