Effect of Surface Ionization on Wetting Layers

We generalize a surface ionization model due to Langmuir to liquid mixtures of polar and nonpolar components in contact with ionizable substrates. When a predominantly nonpolar mixture is near a miscibility gap, thick wetting layers of the conjugate polar phase form on the substrate. Such charged layers can be much thicker than similar wetting layers stabilized by dispersion forces. This model may explain the 0.4- to 0.6-{μ}m-thick wetting layers formed in stirred mixtures of nitromethane and carbon disulfide in contact with glass.