Position of the neutral surface in charged monolayers

Abstract

Curvature elasticity of monolayers can be described in terms of elastic moduli. These moduli depend on the position of the neutral surface (surface of inextension during pure bending). Based on a combination of a mean field theory of chain packing and a head group contribution for amphiphilic molecules, the position of the neutral surface is determined. The electrostatic part of charged molecuels is treated within the framework of the electric double layer. The neutral surface lies nearly in the middle of the region in which a nonzero pressure is acting. Its position is mainly determined by the mechanical pressure and not by the electrostatic contribution. Although the main part of the bending rigidity modulus comes from the chain region, the electrostatic contribution can be several k _B T.