The image-charge forces in thin films of solutions with non-polar solvent.

The image-charge forces appearing due to polarization of phases, confining the liquid film, by the electric field of polar solute molecules are analyzed. The main attention is focused on non-symmetric systems. The consideration of image-charge effects of different types indicates that the contribution from diffusely distributed solute molecules is weak and hardly affects film stability. It is shown that the correlation interaction between layers adsorbed on opposite interfaces is also not very essential for the system, at least for the gaseous adsorbed layer. The appreciable force found is due to the interaction between the relatively dense adsorbed layer and its images. The origin of a strong force in that case is associated with the variation of solute adsorption with film thickness. The calculated magnitude of image-charge forces on the basis of parameters typical for solutions in hydrocarbon solvents are large enough to dominate in the film force balance. Some experimental observations are discussed within the framework of the developed approach.