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

众所周知，液态汞在环境条件下很难弄湿玻璃或蓝宝石等非金属物质。然而，该项目的首席研究员姚在1996年发现，水银在接近液气临界点(1478℃，167 Mpa)的高温高压条件下湿润蓝宝石衬底，润湿膜的厚度在压力-温度平面上的一条直线上不连续地跳跃。这是一级相变，称为预润湿相变。在本工作中，我们首次研究了蓝宝石衬底上汞润湿膜在预润湿临界点附近的静态和动态涨落，并通过测量热辐射强度来观察界面上的静态涨落。这种方法是基于这样一个事实，即热辐射强度包含关于样品界面处的反射率和漫射散射截面的信息(基尔霍夫的L…更多)。我们从观测到的热辐射强度成功地推断出润湿膜的涨落。在这项测量中，采用了一种新的准直器系统来消除样品附近材料的影响。我们发现临界涨落的横向关联长度为几百个压力计，远大于润湿膜的厚度(~10 nm)。其次，我们利用动态光散射技术研究了预湿临界现象的动力学。观测到的自相关函数中的振荡成分(频率ω、阻尼比Γ)强烈地表明，光被形成在润湿膜表面的表面波散射。当压力从气液共存线降低到预润湿线时，ω和Γ均呈现快速上升的趋势。而在预润湿临界点附近，由于临界点的减速而减小。通过这种方式，本项目成功地实现了对二维流体汞的静态和动态涨落的直接观测。较少

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