Effective electrostatic forces between two neutral surfaces with surface charge separation: valence asymmetry and dielectric constant heterogeneity

Abstract

Based on CDFT calculations, we study new features of surface electrostatic force (SEF) between two face-to-face overall neutral surfaces, each of which is comprised of atomic scale strip shape charge distribution and is immersed in +2:−1 electrolyte. Dielectric constant of near surface fluid is lower than that of distant fluid. Ion valence and dielectric constant heterogeneity effects are reflected in the following aspects. (i) For asymmetrical configuration of the strip shape charge distribution, if the coexistence bulk mole concentration is high like , one repulsion peak of the SEF appears at approximately two times the ion diameter and the peak height increases obviously with the ion valence and the strip shape domain width ; however, for low value, like , the ion valence almost does not cause any effect on the SEF shape and strength at small distances except that the higher valence ion causes a higher decaying rate of the SEF with the surface separation. (ii) For the case of the asymmetrical configuration and bivalent ion, strength of the small distance attractive SEF always reduces with the value, and is positively correlated with the value except when the value is high and the domain surface charge strength is low. (iii) The symmetrical strip shape charge distribution is an efficient way in inducing the attractive SEF in presence of bivalence ions even if the value is low down to ; the attraction strength is positively correlated with the value. (iv) The ion adsorption, playing a key role in influencing the SEF for the present overall neutral two-surface system, generally increases with the value, and far higher than that relevant to two similarly charged surfaces with equal value. (v) The lower surface fluid dielectric constant accords both the force and potential curves with new features like alternative mode of attraction and repulsion even in low bulk concentration, big strength in comparison with the average thermal energy, and large insensitivity to the surface charge distribution patterns and ion valence.