The influence of discrete surface charges on the force between charged surfaces

Abstract

The force between two parallel charged flat surfaces, with discrete surface charges, has been calculated with Monte Carlo simulations for different values of the electrostatic coupling. For low electrostatic coupling (small counterion valence, small surface charge, high dielectric constant, and high temperature) the total force is dominated by the entropic contribution and can be described by mean field theory, independent of the character of the surface charges. For moderate electrostatic coupling, counterion correlation effects lead to a smaller repulsion than predicted by mean field theory. This correlation effect is strengthened by discrete surface charges and the repulsive force is further reduced. For large electrostatic coupling the total force for smeared out surface charges is known to be attractive due to counterion correlations. If discrete surface charges are considered the attractive force is weakened and can even be turned into a repulsive force. This is due to the counterions being strongly correlated to the discrete surface charges forming effective, oppositely directed, dipoles on the two walls.

Coarsegrained modeling and electrostatics of phospholipid monolayers

“…The results presented show that the common approach of dividing a generic interface into a Stern Layer, where counterions are strongly interacting, and a diffuse layer, which at least for dilute concentrations can be described within PB theory, is only valid for monovalent counterions and becomes grossly inaccurate for divalent counterions at any surface charge and electrolyte concentration: At low surface charge (high molecular area) because the effects of charge discreteness extend up to a distance of a L /3, while at high surface charge (small molecular area), counterions within the diffuse layer are strongly correlated with the ones within the Stern layer, thus negating any approximation where the Stern layer is approximated as a uniform surface charge. The differences between the osmotic pressure of a plane with discrete and uniform charges discussed in [106,107] is in agreement with these findings.…”

Cation effects on haemoglobin aggregation: balance of chemisorption against physisorption of ions

“…The discrepancy may be tentatively attributed to the mean-field smeared surface charge applied here, neglecting the discrete nature of binding sites as well as the specific amino acid residues hosting the carboxylate and amine sites, which is included in molecular dynamics simulations. Discrete surface charges tend to increase counterion physisorption, increasing repulsion (or diminishing attraction) between surfaces [50]. Anions are rsfs.royalsocietypublishing.org Interface Focus 7: 20160137 counterions for the mildly positive haemoglobin surface charge found in our model.…”

Density profiles and solvation forces for a Yukawa fluid in a slit pore

“…In the future we hope to study plates with more complex interactions, including heterogeneous surfaces, which are physically relevant, and have been shown to induce complex behavior. [55][56][57] 8. The effective potential is calculated in the HNC approximation and plotted for various intensities of wall-particle attraction.…”