(26c) Effects of Charge Discreteness on Electrostatic Interparticle Interactions in Colloidal Dispersions

Solid-liquid interfaces are ubiquitous in natural and engineered environments. Processes like filtration, deposition, aggregation, transport of colloidal particles, phase behavior of colloidal suspensions, and organization of biopolymers and polyions in different structures are governed by the interactions between solid-liquid interfaces. Traditionally, these interactions have been described by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. DLVO constitutes a mean-field theory that accounts for electrostatic interactions between uniformly charged surfaces embedded in solutions containing non-interacting ions that are modeled as point charges. Although the DLVO theory can be applied to cases within certain restrictions, many deviations between experimental observations and theoretical predictions have been reported in the literature. In this work, we present a study on the effects of the discrete nature of surface charge and electrical double layer charge (EDL). A combination of molecular modeling and atomic force microscopy were utilized to probe the behavior of the EDL, the EDL interactions, and the development of surface charge in solutions containing symmetric and asymmetric electrolytes. We report on the occurrence of size exclusion effects, like-charge attraction, and surface charge heterogeneities, phenomena not predicted by the DLVO theory. These phenomena can be anticipated just by considering the discrete nature of surface charge and charge distribution within the EDL.