Thickness of the Liquid-Vapor Wetting Layer

In certain binary solutions the lower of the two liquid phases forms a layer which intrudes between the upper liquid phase and the vapor. The intruding layer's thickness (measured by ellipsometry) was between 70 and 400 Å. It varied approximately as $L^{-\frac{1}{3}}$ where $L$ is the height spanned by the upper liquid phase. This behavior was predicted by de Gennes using the idea that the long-ranged part of the intermolecular potential governs the layer's thickness. Deviations from $L^{-\frac{1}{3}}$ behavior occur near consolute points.