Self-consistent field theory of two-component phospholipid membranes

This paper extends and applies a self-consistent field theory of compressible, fully hydrated phospholipid bilayers to binary mixtures. The mixtures contain two kinds of lipids, which have identical head groups but different acyl chain lengths. The formalism we develop allows for the calculation of a range of thermodynamic and structural properties for systems at equilibrium, including the compatibility of the two components, the equilibrium phase, the bilayer thickness, the orientational order parameter profiles, and the ordering environment as a function of depth within the layer. Our focus in this paper is on the mutual effects of the different chains on each other, and the effects of the local environment on the order parameter of each segment in the chains, for systems in the fluid phase. We include an analysis of a feature of the order parameter profile identified as a "second plateau" by Morrow and co-workers [Biochemistry 32, 290 (1993)].