Direct observation of static and dynamic fluctuations in two-dimensional fluid mercury

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It is well known that liquid mercury hardly wets non-metallic substances such as glasses or sapphire under ambient conditions. However, M.Yao (the head investigator of this project) found in 1996 that mercury wets sapphire substrate under high temperature and pressure conditions near the liquid-gas critical point (1478℃, 167MPa), and that the thickness of the wetting film jumps discontinuously at a line on the pressure-temperature plane. This is the 1st order phase transition called the prewetting transition. In the present work, we studied the static and dynamic fluctuations in the mercury wetting film on the sapphire substrate near the prewetting critical point for the first time in the world.We observed the static fluctuations at the interface by measuring the thermal radiation intensity. This method is based on the fact that the thermal radiation intensity contains information on the reflectivity and the diffuse scattering cross section at the interface of the sample (Kirchhoff's l … More aw). We deduced successfully the fluctuation of the wetting film from the observed thermal radiation intensity. In this measurement, a new collimator system was employed to eliminate the contribution from the materials near the sample. We found that the lateral correlation length of the critical fluctuations is several hundred manometers, which is much larger than the thickness of the wetting film (〜10nm).Next, we studied the dynamics of the prewetting critical phenomena by using dynamic light scattering techniques. The oscillatory component (frequency ω, damping ratio Γ) in the observed autocorrelation function strongly suggests that the light is scattered by the surface wave formed on the surface of the wetting film. When the pressure is decreased from the liquid-gas coexistence line to the prewetting line, both ω and Γ show rapid increase. Near the prewetting critical point, on the other hand, they decrease due to the critical slowing down. In this way, the direct observation of static and dynamic fluctuations in the two-dimensional fluid mercury has successfully been achieved in this project. Less