Electrostatic interactions in two-component membranes

(Received 9 April 1993, accepted 25 May 1993)

Abstract
The effect of electrostatic interactions on membrane undulations is examined. We consider a mixed membrane consisting of neutral and charged amphiphiles in an aqueous solution. In general, this system may exhibit a non-uniform surface charge density. Two limiting cases are distinguished: quenched surface-charge distribution; and annealed inplane distribution which is coupled to an undulation mode. For the former case the electrostatic free energy of an undulating membrane is calculated in the limit of strong ionic solution. Spatial modulations of the surface charge density are found to induce a local spontaneous curvature in a single monolayer. In addition, the electrostatic contribution to the elastic bending modulus is obtained for a general non-uniform surface-charge density. In the latter case of a self-adjusting (annealed) membrane, an electrostatic coupling between the inplane distribution and the membrane curvature produces an added effective interaction which stabilizes modulated phases.