Depletion forces due to image charges near dielectric discontinuities

Abstract

The depletion force is an effective inter-particle attractive interaction that is entropically driven by the exclusion of co-solvent molecules. For large co-solvents, such as polymers, the exclusion is primarily driven by excluded volume interactions. However, the exclusion of co-solvents, such as electrolytes, can be caused by other mechanisms. In this review, we summarize the literature on interparticle depletion forces that arise from repulsive image-charge forces between low-dielectric particles and electrolytes. In particular, we emphasize the results from a variational perturbation theory for describing the salting-out behavior observed in moderately concentrated salt solutions. The theory predicts an unscreened force with a range given by the Bjerrum length and a magnitude proportional to the osmotic pressure of the salt solution. The force becomes significant at the same salt concentration where salting-out behavior is typically observed.

Forces between silica particles in the presence of multivalent cations

“…At shorter distances, additional attractive forces were reported, especially in the presence trivalent cations [17][18][19]. The latter attractive component could be related to ion correlation effects, surface charge heterogeneities, charge fluctuations, or image charges [20][21][22][38][39][40][41].…”

Linear and ring polymers in confined geometries

“…The improvement of the experimental technique allowed even to measure with high accuracy the depletion force which arises between a single colloidal particle and a wall [8][9][10]. Furthermore the force enters into a complex force balance with other intercolloidal interactions, such as DLVO, hydration, hydrophobic interaction [4,5,11]. Therefore it is sometimes challenging to separate and quantify its contribution.…”

Understanding Depletion Induced Like-Charge Attraction from Self-Consistent Field Model

“…When the separation between surfaces is at the range of the particle diameter, they are attractive due to this depletion interaction [2,55]. In electrolytes, this attractive distance can be much larger, comparable with the Debye screening length due to the long-range nature of electrostatic interaction [15]. In this sense, the attractive Van der Waals and the Casimir force [14,31,54] can be ignored in the LCA analysis.…”