Influence of solvent granularity on the effective interactions between two overall neutral surfaces with quenched charge heterogeneity

By using classical density functional theory of an electrolyte solvent primitive model (SPM), we investigate influences of solvent granularity on the effective interactions between two overall neutral planar surfaces with quenched charge heterogeneity over atomic length scale. Main conclusions are summarized as follows: (i) with consideration of the solvent granularity, the potential energy curves can (but not always) be highly oscillatory with a period approximately equal to the particle diameter. (ii) The present u(elec)* curve can change obviously with the bulk electrolyte concentration of the SPM in contrast with the homogeneously charged surfaces, but the concentration dependence of the u(ele)(c)* curve will decrease as the charge separation extent decreases. (iii) Surface charge distributions, electrolyte types and bulk concentrations influence on the u(elec)* curve synergistically. For asymmetrical surface charge distributions, the electrolyte types and charge separation extent do not influence the overall u(elec)* curve shape evidently except that the first valley moves down with the electrolyte valency; by contrast, the overall morphologies of the u(elec)* curves for symmetrical surface charge distributions show features: first, for high valency salt and low bulk concentrations the u(e)(lec)* is purely repulsive; only after the concentration becomes high enough, the alternating repulsive peaks and attractive valleys start appearing but still with weak strength. Second, in the presence of only low valency salt, the u(elec)* curves approximately as a whole (particularly the main valley) move up at low concentrations, and then move down at higher concentrations. Third, the concentration effect in the symmetrical surface charge distributions is not so obvious as that in the asymmetrical distributions. Using liquid theory arguments, all of these observations can be explained logically. Significance: 1. Influence of solvent granularity on the potential energy curve is investigated. 2. Influence of quenched charge heterogeneity on effective interaction is analyzed. 3. Concentration dependence of potential curve increases with charge separation extent. (C) 2018 Elsevier B.V. All rights reserved.