FLUID LIPID BILAYERS - INTERMONOLAYER COUPLING AND ITS THERMODYNAMIC MANIFESTATIONS

A fluid membrane of lipid bilayer consists of two individual molecular monolayers physically opposed to each other. This unique molecular ar chitecture naturally necessitates the need to treat a lipid-bilayer me mbrane as one entity of two coupled two-dimensional systems (monolayer s), each of which possesses ''in-plane'' degrees of freedom that chara cterize its physical or chemical state. Thermally excitable deformatio ns of a Lipid bilayer in its geometrical conformation further impart t o it ''out-of-plane'' degrees of freedom. In this paper we discuss the issue of intermonolayer coupling in terms of a phenomenological model that describes the necessary types of degrees of freedom and their in terplay, which reflects different modes of intermonolayer coupling. Fu rthermore, we investigate! based on the phenomenological model, the ma nifestations of the intermonolayer coupling both in the lateral orderi ng processes of the ''in-plane'' degrees of freedom and in the conform ational behavior of the bilayer membrane.