Surface polarization strongly influences electrostatics in a nonlocal medium

Abstract

Electrostatics in the solution phase is governed by free electrical charges such as ions, as well as by bound charges that arise when a polarizable medium responds to an applied field. In a local medium, described by a constant dielectric permittivity, the sign of the far-field electrostatic potential distribution around an object is governed by its electrical charge. We demonstrate significant departures from this expectation in a nonlocal medium characterized by a wave vector-dependent dielectric function. Here, surface polarization due to the solvent, or indeed non-solvent dipoles, may wield significant influence at large distances. The polarization correlation length may not only significantly augment the effective screening length, but we also show that the electrical contribution from polarization can compete with and even invert the sign of the electrical potential and the field arising from charge alone. These results hold ramifications for a range of apparently anomalous electrically governed observations such as underscreening, electrophoretic mobilities of charge-neutral objects, and long-ranged attraction between like-charged entities in water and other solvents.