Mallamace Francesco, Corsaro Carmelo, Mallamace Domenico, Fazio Enza, Chen Sow-Hsin
Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Dipartimento di Scienze Matematiche e Informatiche, Scienze Fisiche e Scienze della Terra (MIFT), Università di Messina I-98166, Messina, Italy.
J Chem Phys. 2019 Jul 28;151(4):044504. doi: 10.1063/1.5095687.
The bulk liquid water density data (ρ) are studied in a very large temperature pressure range including also the glass phases. A thorough analysis of their isobars, together with the suggestions of recent thermodynamical studies, gives evidence of two crossovers at T and P above which the hydrogen bond interaction is unable to arrange the tetrahedral network that is at the basis of the liquid polymorphism giving rise to the low density liquid (LDL). The curvatures of these isobars, as a function of T, are completely different: concave below P (where maxima are) and convex above. In both the cases, a continuity between liquid and glass is observed with P as the border of the density evolution toward the two different polymorphic glasses (low and high density amorphous). The experimental data of the densities of these two glasses also show a markedly different pressure dependence. Here, on the basis of these observations in bulk water and by considering a recent study on the growth of the LDL phase, by decreasing temperature, we discuss the water liquid-liquid transition and evaluate the isothermal compressibility inside the deep supercooled regime. Such a quantity shows an additional maximum that is pressure dependent that under ambient conditions agrees with a recent X-ray experiment. In particular, the present analysis suggests the presence of a liquid-liquid critical point located at about 180 MPa and 197 K.
研究了大量液态水的密度数据（ρ），其温度压力范围非常大，还包括玻璃相。对其等压线进行了全面分析，并结合近期热力学研究的建议，发现了在温度T和压力P处的两个交叉点，高于此点，氢键相互作用无法排列构成液体多态性基础的四面体网络，从而产生低密度液体（LDL）。这些等压线的曲率作为温度T的函数完全不同：在压力P以下（此处有最大值）为凹形，在压力P以上为凸形。在这两种情况下，都观察到液体和玻璃之间的连续性，以压力P作为密度向两种不同多晶型玻璃（低密度和高密度无定形）演变的边界。这两种玻璃密度的实验数据也显示出明显不同的压力依赖性。在此，基于对大量水的这些观察，并考虑到最近关于LDL相生长的一项研究，通过降低温度，我们讨论了水的液-液转变，并评估了深度过冷状态下的等温压缩率。这样一个量显示出一个额外的最大值，它与压力有关，在环境条件下与最近的一项X射线实验结果一致。特别是，目前的分析表明存在一个液-液临界点，位于约180MPa和197K处。
