SHAPE TRANSITIONS OF DOMAINS IN INSOLUBLE MONOLAYERS - DERIVATION AND USE OF COMPUTATIONALLY EFFICIENT FORMULATIONS OF THE ELECTROSTATIC ENERGY

Dispersed domains in a two-phase insoluble phospholipid monolayer exhibit a myriad of shapes. Domain shapes can be predicted using a free energy analysis put forth by McConnell. One contribution to the free energy of an isolated domain is the electrostatic energy arising from dipolar interactions between lipid molecules. The expression for this electrostatic energy, however, cannot be evaluated analytically and is cumbersome to compute numerically. In this paper, we derive two simplified, yet rigorous, formulations of the electrostatic energy, one being more computationally efficient for circular domains, the other for noncircular domains. We used these rigorous expressions to repeat two previously reported shape calculations that were based on an approximation to the electrostatic energy. Our results differ from the original results by an amount proportional to the domain perimeter, offering a bridge between our energy functional and the approximated one.