Metastable wetting layers.

In the two-phase region of a critical binary liquid mixture a wetting layer of the heavier phase can occur at the upper liquid-vapor surface sufficiently close to the critical temperature. This wetting layer can be either stable or metastable to long-wavelength capillary wave fluctuations on the adjacent critical interface. The stability depends upon the sign and slope of the dispersion force curve F(d). We classify the four main generic shapes for F(d), which determines the stability or metastability of the wetting layer, in terms of the relative magnitudes of the static and visible dielectric constants for the two liquid components. For realistic values of the liquid-mixture parameters we calculate the critical wavelength beyond which fluctuations are unstable and also determine the lifetime of the metastable state. The lifetime can vary from seconds to many hours.