Multilayer wetting phenomenon at a binary liquid-vapor interface. II. Comparison with experiment

The theory of the preceding paper is applied to a binary liquid mixture. The wetting equation has three solutions, and the equilibrium solution is the thermodynamically stable solution which has the lowest wetting surface tension. When the results are compared with the experiments of Beaglehole on the ternary mixture ${\mathrm{CH}}_3$OH-${\mathrm{C}}_6$ ${\mathrm{H}}_{12}$-${\mathrm{H}}_2$O for low water concentration, excellent quantitative agreement is found and two of the three surface transitions observed by Beaglehole are explained within the theory. The third surface transition is believed to be due to a hydrodynamic instability. Beaglehole observed nonwetting behavior for a pure mixture of cyclohexane-methanol. For this system we expect Antonow’s rule to be obeyed only very close to the critical temperature; the addition of water causes Antonow’s rule to be obeyed well below the critical temperature. The wetting equation, which is derived from a modified mean-field theory and which incorporates capillary waves intrinsically within the surface-tension terms, solves a long-standing dilemma which exists between the capillary-wave and the mean-field approach to surfaces; the former approach predicts that the interfacial width will diverge as the gravitational constant g goes to zero, while the latter approach predicts that there will be a finite intrinsic width at zero g. The wetting equation predicts a wetting β layer in zero gravity provided the bulk phases (α-β) separate and an αν liquid-vapor surface exists.