Dipartimento di Matematica e Fisica, Universita' Roma Tre, via della Vasca Navale 84, I-00146 Rome, Italy.
Center for Polymer Studies and Department of Physics, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, USA.
Nat Commun. 2014 Dec 16;5:5806. doi: 10.1038/ncomms6806.
Supercritical water is fundamental in many fields of applications and a precise characterization of the supercritical state is of uttermost importance for this liquid. In a fluid, when moving from the critical point into the single-phase region, the thermodynamic response functions show maxima reminiscent of the critical divergence. Here we study the thermodynamic properties of water in the supercritical region by analysing both available experimental data and our computer simulation results. We find that the lines connecting the maxima of the response functions converge on approaching the critical point in a single line, the Widom line. We further show that the Widom line coincides with a crossover from a liquid-like to a gas-like behaviour clearly visible in the transport properties. These thermodynamic and dynamic features show that the supercritical state in water is far more complex than what was so far believed, indicating a new perspective in the characterization of the thermodynamics of this state.
超临界水在许多应用领域中都很重要，因此对这种液体的超临界状态进行精确描述至关重要。在流体中，从临界点进入单相区时，热力学响应函数会出现类似于临界点发散的最大值。在这里，我们通过分析现有实验数据和计算机模拟结果来研究超临界区水中的热力学性质。我们发现，在接近临界点时，连接响应函数最大值的线会汇聚到一条线上，即 Widom 线。我们进一步表明，Widom 线与从液态到气态的转变相吻合，这在输运性质中清晰可见。这些热力学和动力学特征表明，水的超临界状态比迄今为止人们所认为的要复杂得多，这为该状态的热力学特性的描述提供了新的视角。
