Unraveling the Combined Effects of Dielectric and Viscosity Profiles on Surface Capacitance, Electro-Osmotic Mobility, and Electric Surface Conductivity

摘要

We calculate the electro-osmotic mobility andnsurface conductivity at a solid−liquid interface from a modifiednPoisson−Boltzmann equation, including spatial variations of thendielectric function and the viscosity that where extracted previouslynfrom molecular dynamics simulations of aqueous interfaces. Thenlow-dielectric region directly at the interface leads to a substantiallynreduced surface capacitance. At the same time, ions accumulate intona highly condensed interfacial layer, leading to the well-knownnsaturation of the electro-osmotic mobility at large surface chargendensity regardless of the hydrodynamic boundary conditions. Thenexperimentally well-established apparent excess surface conductivitynfollows from our model for all hydrodynamic boundary conditions without additional assumptions. Our theory fits multiplenpublished sets of experimental data on hydrophilic and hydrophobic surfaces with striking accuracy, using the nonelectrostaticnion−surface interaction as the only fitting parameter.