水和其他流体的“尖锐扭结近似”的有效性
Validity of the "sharp-kink approximation" for water and other fluids
摘要：
液滴在固体表面上的接触角是作用在液体分子和固体表面之间的基本原子尺度力的直接量度。在这项工作中，有效性进行评估的一个简单的方程，它近似地涉及到一个表面上的液体的接触角，它的密度，它的表面张力，和有效的分子表面电位。这个方程是在尖锐扭结近似下推导出来的，其中假设液体的密度分布在基底的一个分子直径内急剧下降。发现该方程满意地再现了氦在碱金属表面的接触角随温度的变化关系。根据室温附近预测和测量的接触角的比较，该方程似乎也适用于液体，如水在固体表面，如金和石墨。然而，我们得出结论，为了充分测试该方程对诸如水的流体的适用性，仍然有必要测量接触角的温度依赖性。我们假设，静电力的影响可以随温度增加，潜在地驱动润湿温度比使用当前理论预测的高得多并且更接近临界点，或者更低，更接近室温。
英文摘要：
The contact angle of a liquid droplet on a solid surface is a direct measure of fundamental atomic-scale forces acting between liquid molecules and the solid surface. In this work, the validity is assessed of a simple equation, which approximately relates the contact angle of a liquid on a surface to its density, its surface tension, and the effective molecule-surface potential. This equation is derived in the sharp-kink approximation, where the density profile of the liquid is assumed to drop precipitously within one molecular diameter of the substrate. It is found that this equation satisfactorily reproduces the temperature-dependence of the contact angle for helium on alkali metal surfaces. The equation also seems be applicable to liquids such as water on solid surfaces such as gold and graphite, based on a comparison of predicted and measured contact angles near room-temperature. Nevertheless, we conclude that, to fully test the equation's applicability to fluids such as water, it remains necessary to measure the contact angle's temperature-dependence. We hypothesize that the effects of electrostatic forces can increase with temperature, potentially driving the wetting temperature much higher and closer to the critical point, or lower, closer to room temperature, than predicted using current theories.
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