Image charge theory

Polar M/C interfaces have only been studied sparsely. The polar (111) and nonpolar (100) Cu/MgO interfaces were compared in a slab calculation within the LDA. ° As expected from the image model theory, the polar interface displayed a considerably higher work of separation. In addition, these authors found a larger charge transfer and Cu-MgO orbital mixing for the polar interface. 

The situation is still more complex in the presence of surfactants. Recently, a self-consistent electrostatic theory has been presented to predict disjoining pressure isotherms of aqueous thin-liquid films, surface tension, and potentials of air bubbles immersed in electrolyte solutions with nonionic surfactants [53], The proposed model combines specific adsorption of hydroxide ions at the interface with image charge and dispersion forces on ions in the diffuse double layer. These two additional ion interaction free energies are incorporated into the Boltzmann equation, and a simple model for the specific adsorption of the hydroxide ions is used for achieving the description of the ion distribution. Then, by combining this distribution with the Poisson equation for the electrostatic potential, an MPB nonlinear differential equation appears. 

There are various ways to model the distributions of chain conformations near surfaces. Here we describe an approach based on a reflectance principle. It resembles the image charge approach in the theory of electrostatic interactions (see Chapter 21, page 399). 

For the time being, there is no generally accepted theory of the repulsive hydration force. It has been attributed to various effects solvent polarization and H-bonding [323], image charges [324], nonlocal electrostatic effects [325], and the existence of a layer of lower dielectric constant, e, in a vicinity of the interface [326,327]. It seems, however, that the main contribution to the hydration repulsion between two charged interfaces originates from the finite size of the hydrated counterions [328], an effect which is not taken into account in the DLVO theory (the latter deals with point ions). 

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