Wetting of a binary liquid mixture on glass

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Abstract
When two fluids coexist above a substrate, a thin layer of the upper fluid often intrudes between the lower fluid and the substrate. For such intruding layers to be stable against gravity, it is necessary that the short- and long-range interactions between the substrate and the two fluid phases both favor the presence of the upper phase near the substrate. We consider the consequences of this for the carefully studied case of partially miscible mixtures of nitromethane and carbon disulfide in contact with borosilicate glass. A careful calculation based on the Dzyaloshinskii-Lifshitz-Pitaevskii theory of dispersion forces shows that dispersion forces do not favor the formation of the nitromethane-rich layer that has been observed to intrude between the carbon disulfide–rich phase and the glass. If the observed layers are an equilibrium phenomenon, their existence requires a protagonist force stronger than dispersion forces. It is plausible that electrostatic forces which arise from ionization of the glass surface are the required long-range force.