Mercury wetting film on sapphire - art. no. 051601

We have measured optical properties of a mercury wetting film on sapphire u nder high temperature and high pressure near the liquid-gas critical point of mercury by using a newly developed 45 degrees reflection technique. We h ave analyzed the experimental data to deduce the density, the thickness, an d the coverage of the wetting film quantitatively as functions of pressure and temperature. As a first approximation, we have assumed a slab model for the density profile of the wetting film, and found that the density of the wetting film d(slab) is much smaller than that of bulk liquid at the liqui d-vapor coexistence curve. This result is consistent with the Lifshitz theo ry, from which we may predict that the sapphire substrate prefers wetting h im with density lower than the metal-nonmetal transition. When the temperat ure is close enough to the prewetting critical temperature T-pw(c) the effe ctive slab density d(slab) shows a sharp decrease as the pressure approache s the liquid-gas coexistence. This indicates that the slab model is not suf ficient to describe the shape of the wetting film, and a smooth variation o f the density has to be taken into account. In the prewetting supercritical region, two anomalies an observed in the reflectances. Possible mechanisms of these anomalies are discussed.