Spontaneous formation of lecithin bilayers at the air–water surface

Abstract

THE energetics of formation of various surface film states of dimyristoyl lecithin (DML) has been recently obtained from equilibrium spreading pressure π_e measurements¹. One result from that study, but not reported then, was the formation of a new equilibrium lecithin surface phase. Its existence was deduced solely from formal thermodynamic arguments based on the Gibbs phase rule, and therefore reporting of the new surface phase was deferred until more direct experimental evidence was available for describing its properties. We have now characterised this new surface phase by measuring the surface concentration of DML films and have found the concentration to be double that of a close-packed monomolecular film. Before presenting these results and their implications, we summarise the arguments which led to the prediction of the new lecithin surface phase.