ELECTRIC DOUBLE-LAYER NEAR SOFT PERMEABLE INTERFACES .2. NONLOCAL THEORY

We have considered the electrostatic field distribution near a soft pe rmeable interface in an aqueous solution, taking into account the spat ial variation of the dielectric permittivity within the framework of a nonlocal electrostatic theory. We have analyzed the effect of the int erface thickness as well as different combinations of the surface elec tric charge and dipole densities. We have shown that the electric fiel d potential is described in such systems by two exponential terms, one of which is determined by Debye screening, and the other by the nonlo cal polarization of the aqueous solution. For certain combinations of the electric charge and dipole densities the potential can become nonm onotonic. We have shown that, in addition to the electric charge and d ipole densities, a significant parameter that determines the electric field distribution in electric double layers is the interface thicknes s. We discuss how the results obtained can assist in understanding mod el lipid/protein systems, measurements of surface potentials, and surf aces of biological membranes.