The role of image charges in the interactions between colloidal particles

Abstract

The dielectric interiors of colloidal particles are responsible for dispersion (van der Waals) interactions. However, these dielectric regions also alter the manner in which charges, such as on ions or other colloidal particles, interact with each other, due to the induction of charges at the dielectric interfaces. The impact of these induced charges can be represented in terms of 'image charges'. These image charges result in an ion depletion layer in the vicinity of low dielectric bodies. This depletion layer is responsible for the increase in the surface tension of water upon the addition of electrolytes. In the case of colloidal particles, this depletion layer also leads to an 'electrostatic depletion force' with a range of the order of a Bjerrum length. The relevance of this force to the salting out of proteins is discussed. This electrostatic depletion force is directly analogous to the entropically driven depletion force (due to excluded volume). Although image charge effects have been known, their influence on the behavior of colloidal systems, especially in the presence of mobile ions, has generally not been accounted for (e.g., DLVO theory). We review the previous theoretical and simulation studies of how image charges influence the properties of electrolyte and colloidal systems and discuss the relevance of these effects on experimental system

The influence of excluded volume and excess ion polarisability on the capacitance of the electric double layer

“…The importance of these interactions is visible in, for example, the differences between the differential capacitance of the same electrolyte at electrodes made from different materials, or even at different crystal faces of the same electrode material [52]. Polarization of the electrode itself would lead to an "image charge" interaction [47,48,53] between it and the ions in the system. This interaction would typically be attractive for all counter-ion and co-ion species, however, its magnitude would depend on properties, such as the polarizability, of the ions.…”

Charge regulation and ionic screening of patchy surfaces

“…Since every ion close to a body with a lower dielectric constant will be repelled by its own image charge, typically a small depleted zone of ions appears close to the surface. This image-charge effect is, however, only significant if (κλ B 1), 45 and can thus be ignored in most aqueous electrolytes. Moreover, although we do not include this correction in our model, the effect of image charges of the ionic double layer is naturally included by the chosen boundary condition at the surface z = 0.…”

Depletion forces due to image charges near dielectric discontinuities

“…Within Lifshitz theory, the zero-frequency contribution to the dispersion interaction energy F is related to the Green's function of the Poisson equation [31,32,33]…”