Abstract
Different types of surface forces, acting in the films of pentane, hexane, and heptane on water are discussed. It is shown that an important contribution to the surface forces originates from the solubility of water in alkanes. The equations for the distribution of electric potential inside the film are derived within the Debye-Hückel approximation, taking into account the polarization of the film boundaries by discrete charges at water-alkane interface and by the dipoles of water molecules dissolved in the film. On the basis of above equations we estimate the image charge contribution to the surface forces, excess free energy, isotherms of water adsorption in alkane film, and the total isotherms of disjoining pressure in alkane film. The results indicate the essential influence of water/alkane interface charging on the disjoining pressure in alkane films, and the wettability of water surface by different alkanes is discussed.
Highlights
The wetting of water by oils and the oil spreading on water are important fundamental and environmental issues, due to the significant increase in the area of the oil spill caused by spreading and its impact on the marine life and water
In our previous theoretical studies [2,3] we have shown that some of the peculiarities of wetting of water and brine solutions by alkanes from pentane to octane can be described by taking into account the image charge forces
Waals reasonabletotoassociate associate mechanism of these additional with the of water dissolved in alkane films
Summary
The wetting of water by oils and the oil spreading on water are important fundamental and environmental issues, due to the significant increase in the area of the oil spill caused by spreading and its impact on the marine life and water. The existence of very thin, on the order of a few molecular diameters, wetting oil films in equilibrium with a droplet on a water surface contradicts to theoretical predictions, based on van der Waals forces. The analysis, presented in [2] considers the electrostatic energy of dissolved water molecules in the field of images of dipoles in confined phases. In this study we will present the theoretical analysis of surface forces, arising due to interaction of dipoles of water molecules, adsorbed in the hydrocarbon film, with both the polarized film boundaries and with charges at the water/alkane interface. We will discuss the role of weak water solubility in alkanes in the stability of alkane wetting films and in the wettability of aqueous phases by oils
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