On the physics of both surface overcharging and charge reversal at heterophase interfaces

Abstract

The conventional paradigm for characterizing surface overcharging and charge reversal is based on the so-called Stern layer, in which surface dissociation reaction and specific chemical adsorption are assumed to take place. In this article, a series of Monte Carlo simulations have been applied to obtain useful insights into the underlying physics responsible for these two kinds of anomalous phenomena at the interface of two dielectrics, with special emphasis on the case of divalent counterions that are more relevant in natural and biological environments. At a weakly charged surface, it is found that independent of the type of surface charge distribution and the dielectric response of the solution, the overcharging event is universally driven by the ion size-asymmetric effect. Exceptionally, the overcharging still persists when the surface is highly charged but is only restricted to the case of discrete surface charge in a relatively low dielectric medium. As compared to the adsorption onto the homogeneously smeared charge surface that has the same average affinity for counterions, on the other hand, charge reversal under the action of a dielectric response can be substantially enhanced in the discrete surface charge representation due to strong association of counterions with interfacial groups, and the degree of enhancement depends in a nontrivial way on the reduction of the medium dielectric constant and the steric effects of finite ion size. Rather interestingly, the charge reversal is of high relevance to the overcharging of interfaces because the overwhelming interfacial association forces the coions closer to the surface due to their smaller size than the counterions. Upon the addition of a monovalent salt to the solution, the interfacial association with divalent counterions makes surface overcharging and charge reversal widely unaffected, in contrast to the prevailing notion that screening of surface charge of a homogeneous nature is determined by the competitive effects between size-exclusion effects and energetic contributions. Overall, the present work highlights that the complex interplay between the electrostatic and steric interactions should be coupled to the realistic character of surface charge to establish a faithful description of the overcharging and charge reversal at heterophase interfaces.

Assessing the accuracy of three classical density functional theories of the electrical double layer

“…Given the systematic nature of the simulation (and DFT) parameters studied, we naturally reproduce some of the results previously published by others, including seminal works using MC by Torrie and Valleau [19,20,36], as well as other MC simulations, for example on charge inversion [37][38][39][40][41]. Cases have also been studied using theories other than DFT, including seminal studies by Blum, Henderson, and others [42] using integral theories like the hypernetted chain [43,44].…”

Theoretical investigation of a polarizable colloid in the salt medium

“…There are many general theories for polarizable colloids in salt environments which are not restricted to the weak coupling limit 26,[33][34][35][36][37] . As a result, it is important to observe the performance of the ET for multivalence salt.…”

Debye-Hückel Free Energy of an Electric Double Layer with Discrete Charges Located at a Dielectric Interface

“…The nearestneighbor distances between charges on biomolecular aggregates are often significantly larger than the Debye length. For example, the nearest-neighbor distance between the charges on a lipid membrane with 10% anionic lipids is about three times larger than the Debye length, necessitating accounting for the discreteness of the charge when using free energies to model membrane properties, such as domain formation, bending stiffness, spinodal decomposition, charge reversal [44,45], and renormalization [46], or differential capacitance [47,48]. Our present work may assist in this kind of modeling.…”