Ligth water, heavy water, and sodium chloride aqueous solutions under extreme conditions to shed light on water anomalies and structural properties

水和水溶液无处不在，涉及无数的自然现象和工艺过程。水在所有液体中脱颖而出，因为它的许多物理异常与其复杂的氢键网络有关，但人们对它的了解还不完全。我们项目的目标是结合物理学和地球科学的研究人员的努力，获得关于极端条件下的水和水溶液的新知识。一方面，我们将探索在负压下的拉伸液体状态。然后，液体相对于蒸汽是亚稳的，气泡可能在任何时候成核，使系统恢复平衡。但是，捕获在石英基质中的小液滴在亚稳态时可以达到-100兆帕以上，可以用光子来研究。我们将使用布里渊光谱、可见光拉曼光谱和X射线拉曼光谱来阐明拉伸水的热力学和分子结构。实验不仅将在拉伸的普通水上进行，而且还将在拉伸的重水和含水的氯化钠溶液上进行，因为预计它们将允许进入普通水中找不到的特定特征。具体地说，重水的密度极大值线预计将在实验可达的负压下达到最高温度，而最近在纯水、拉伸水中发现的可压缩性极大值线预计在低盐浓度下变得更加明显。确认或不证实这些特征将对我们理解水及其相图有广泛的影响，包括令人感兴趣的(有争议的)液体多晶化的可能性--水存在两个不同的液体相。另一方面，我们将研究高压和高温条件下的稳定流体状态。水在地质作用(如俯冲带和热液活动)中的一个关键性质是粘度。然而，令人惊讶的是，高压下纯净水的数据很少，咸水则没有。此外，目前的测量技术(钻石顶压室小腔内的滚珠粘度计)具有局限性，可能会受到偏差。我们将实施一种基于直径约100纳米的球体的布朗运动的新技术，以绕过这些限制。这些结果将通过可见光拉曼光谱直接与分子结构联系起来。为了进一步了解，我们将使用x射线拉曼散射光谱，特别是在接近汽液临界点的条件下，研究重水和氯化钠溶液的鲜为人知的结构，评估对离子水合的影响。在此，我们结合我们互补的专业知识，在拉伸、超临界和高密度的极端条件下研究水、重水和氯化钠水溶液，从而更深入地了解流体的微观结构及其与宏观性质的关系。

Water and aqueous solutions are ubiquitous, being involved in countless natural phenomena and technological processes. Water stands out among all liquids because of its numerous physical anomalies related to its complex hydrogen bond network, yet it is not fully understood. The goal of our project is to combine the efforts of researchers in physics and geosciences to gain new knowledge about water and aqueous solutions under extreme conditions. On the one hand, we will explore the stretched liquid state, at negative pressures. The liquid is then metastable with respect to vapor and a bubble may nucleate at any time, bringing back the system to equilibrium. But small liquid droplets trapped in a quartz matrix reach beyond –100 MPa in the metastable state and can be studied with photons. We will use Brillouin, visible Raman and x-ray Raman spectroscopy in order to elucidate the thermodynamics and molecular structure of stretched water. Experiments will be performed not only on stretched ordinary water but also on stretched heavy water and aqueous NaCl solutions, as they are predicted to grant access to specific features, which cannot be found in ordinary water. Specifically, the line of density maxima of heavy water is predicted to reach a maximum temperature at a negative pressure accessible to experiment, while the line of compressibility maxima recentlyfound in pure, stretched water is predicted to become more pronounced with a low salt concentration. Confirming or not these features will have broad implications for our understanding of water and its phase diagram, including the intriguing (debated) possibility of liquid polyamorphism – the existence of two distinct liquid phases of water. On the other hand, we will study the stable fluid state under high pressure and temperature conditions. One key property of water in geological processes (e.g. subduction zones and hydrothermal activity) is viscosity. Yet, surprisingly, data is scarce for pure water at high pressure, and absent for salty water. Moreover, the current measurement technique (rolling ball viscometer inside the small chamber of a diamond anvil cell) has limitations and may suffer from bias. We will implement a new technique based on the Brownian motion of spheres of ca. 100 nm diameter to bypass these limitations. These results will be directly linked to the molecular structure using visible Raman spectroscopy. For further insight, we will use x-ray Raman scattering spectroscopy, particularly to address the less well known structure of heavy water and NaCl solutions at conditions up to near the liquid-vapor critical point, assessing the influence on ion hydration. Herewith, we combine our complementary expertise in order to study water, heavy water, and aqueous NaCl solutions at extreme conditions, in the stretched, supercritical and high-density regimes, giving rise to a deeper understanding of the microscopic structure of the fluids and their relation to macroscopic properties.