QUANTIZED SYMMETRY OF LIQUID MONOLAYER DOMAINS

Theoretical arguments have been developed that the shapes of lipid dom ains at the air-water interface can be understood in terms of a compet ition 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-ra nge electrostatic forces can be expressed in terms of these dipoles. T he present work further tests the theory of domain shapes involving co mpetition between line tension and dipolar forces by observations of t ransitions of circular domains to domains of lower symmetry. These tra nsitions occur when the electrostatic repulsive forces exceed the forc es of line tension lambda. Transitions of circular domains to domains with shapes of lower symmetry are functions of domain radius and the d imensionless parameter lambda/mu2; the experimental results are in acc ord with theory to within the experimental error.