A thermodynamic analysis of the formation of bilayer films

Abstract

A theoretical treatment is given of the conditions for formation of a “bimolecular leaflet” membrane from a thick film separating two aqueous bodies. Some surface-thermodynamic functions recently proposed for films on solids (1) and in particular ΔF c w ff w ( L) , the reversible work of cohesion (back to back) of two oriented monolayer films, are employed. Here the subscript ( L) signifies that, on separation, the film-film interface is replaced by two film-liquid interfaces. This function makes it possible to estimate the energy of cohesion across the mid-plane of a bilayer, and hence the free energy of formation of the bilayer. It is shown that the free energy of formation is generally negative. The limitations on this analysis are discussed, together with the thermodynamic and dynamical factors that would make the bilayer unstable.