Electrostatics of curved fluid membranes: The interplay of direct interactions and fluctuations in charged lamellar phases

Our understanding of the Poisson-Boltzmann electrostatics of curved fluid m onolayers and bilayers of ionic amphiphiles, and its status within the Helf rich bending-energy formulation, is reviewed and subsequently extended. The two limiting scenarios, namely excess salt (non-overlapping interfaces) an d zero salt (counterions only) are briefly discussed to couch their general ization to intermediate screening. This general situation of arbitrary comp osition is treated first within the cylindrical and spherical cell models, to harmonic order in their curvatures, leading on to the geometry of undula ting planar confinement, now harmonic in amplitude but covering the entire spectrum of wavelengths. The latter derivation extends previous results, an d moreover, provides analytic expressions for the electrostatic free energy using theta function developments. This in turn supplies the Hamiltonian f or the generalized harmonic theory of fluctuating lamellar phases with adde d salt. Finally, the statistical mechanical predictions for the area increa se, and relative amplitudes, of bilayer thermal undulations are compared to existing light-scattering data from dilute lamellar phases doped with anio nic surfactant. (C) 1999 Elsevier Science B.V. All rights reserved.