Development of equilibrium domain shapes in phospholipid monolayers.

Fluorescence micrographs of monolayers of L-alpha-dipalmitoylphosphatidylcholine (DPPC) at the air water interface are analyzed. Ordered phase domains in coexistence with the fluid lipid phase change their shapes with time and with lateral pressure. With domains fixed under an electrode and well separated from their neighbours a peculiar instability of the boundary lines is observed. It is ascribed to the onset of an electrostatically induced shape transition. Elaborating the boundary regions where domain fusion and fission, respectively, are observed leads to a model on in-plane dipole orientation.