Caupin Frédéric, Ragueneau Pierre, Issenmann Bruno
Institut Lumière Matière, Université Claude Bernard Lyon 1, CNRS, Institut Universitaire de France, F-69622 Villeurbanne, France.
J Chem Phys. 2024 May 21;160(19). doi: 10.1063/5.0205452.
Light and heavy water show similar anomalies in thermodynamic and dynamic properties, with a consistent trend of anomalies occurring at higher temperatures in heavy water. Viscosity also increases faster upon cooling in heavy water, causing a giant isotope effect, with a viscosity ratio near 2.4 at 244 K. While a simple temperature shift apparently helps in collapsing experimental data for both isotopes, it lacks a clear justification, changes value with the property considered, and requires additional ad hoc scaling factors. Here, we use a corresponding states analysis based on the possible existence of a liquid-liquid critical point in supercooled water. This provides a coherent framework that leads to the collapse of thermodynamic data. The ratio between the dynamic properties of the isotopes is strongly reduced. In particular, the decoupling between viscosity η and self-diffusion D, measured as a function of temperature T by the Stokes-Einstein ratio Dη/T, is found to collapse after applying the corresponding states analysis. Our results are consistent with simulations and suggest that the various isotope effects mirror the one on the liquid-liquid transition.
轻水和重水在热力学和动力学性质上表现出相似的反常现象，重水的反常现象在较高温度下呈现出一致的趋势。重水在冷却时粘度增加也更快，从而导致巨大的同位素效应，在244 K时粘度比接近2.4。虽然简单的温度偏移显然有助于将两种同位素的实验数据合并，但它缺乏明确的依据，会随所考虑的性质而改变数值，并且需要额外的特设比例因子。在此，我们基于过冷水可能存在液 - 液临界点进行了对应态分析。这提供了一个连贯的框架，使得热力学数据得以合并。同位素动力学性质之间的比率大幅降低。特别是，通过斯托克斯 - 爱因斯坦比率Dη/T作为温度T的函数测量的粘度η和自扩散D之间的解耦，在应用对应态分析后被发现得以合并。我们的结果与模拟结果一致，并表明各种同位素效应反映了对液 - 液转变的影响。
