The structure and dynamics of water confined in nanoscale pools: the dynamic crossover

液态水和过冷水的特殊行为已经困扰了科学至少236年，并且仍然被视为当今化学面临的主要挑战（Whitesides & Deutch，Nature 469，21（2011））。有人认为，这种奇怪的行为可能是由热力学转变引起的，甚至可能是第二个临界点。这第二个临界点将终止水的低密度和高密度无定形相之间的共存线。不幸的是，该第二临界点（如果存在的话）和相关的多晶液-液转变难以研究，因为它被认为位于被称为“无人区”的区域中的均质成核温度以下（Angell，Science 319，582（2008））。在最近的初步飞秒光学克尔效应光谱实验中，我们已经表明，在浓缩的低共熔溶液中的水形成纳米尺度的池，其中它保留了许多，如果不是大部分的散装液体特性。最重要的是，这种溶液可以冷却到200 K以下而不结晶（通常在较低温度下形成玻璃），从而首次详细探索“无人区”。结合飞秒光谱与NMR扩散测量的初步实验表明，这些池中的水经历了预测为散装水的液-液转变。因此，建议使用这种纳米池作为纳米级实验室，用于研究液态水和玻璃态水。已经建立了广泛的国际合作，以便能够研究水的结构和动态的不同关键方面。这包括低温粘度测量，大动态范围（飞秒到毫秒）光学克尔效应实验，脉冲场梯度NMR，介电弛豫光谱，太赫兹时域光谱，红外泵浦探测光谱和二维红外光谱。为了确保实验工作的最大影响，与水及其热力学行为的理论和模拟专家保持密切联系至关重要。我们已安排与两个国际理论小组合作，涵盖拟议工作的不同方面。虽然拟议的研究是相对基础性的，但它将产生影响，详见其他地方。该研究解决了EPSRC在纳米科学（液体中的超分子结构），能源（电池和燃料电池电解质中的质子传输和液体结构），生命科学（水在生物分子中和生物分子上的作用）和化学-化学工程界面（水结构在晶体成核中的作用）的优先事项。我们与理论合作者的紧密联系将确保基本见解确实传播给这些信息的“用户”。PI和CI之间的密切工作关系使格拉斯哥成为先进飞秒光谱学的卓越中心。该项目利用这一专业知识和国际合作，使用最先进的先前资助的设备，将PDRA和PGRS沉浸在国际领先的研究中。

The peculiar behaviour of liquid and supercooled water has been baffling science for at least 236 years and is still seen as a major challenge facing chemistry today (Whitesides & Deutch, Nature 469, 21 (2011)). It was suggested that such strange behaviour might be caused by thermodynamic transitions, possibly even a second critical point. This second critical point would terminate a coexistence line between low- and high-density amorphous phases of water. Unfortunately, this second critical point (if it exists) and the associated polyamorphic liquid-liquid transition is difficult to study as it is thought to lie below the homogeneous nucleation temperature in a region known as "no man's land" (Angell, Science 319, 582 (2008)). In recent preliminary femtosecond optical Kerr-effect spectroscopy experiments, we have shown that water in concentrated eutectic solutions forms nanometre scale pools in which it retains many if not most of its bulk liquid characteristics. Most importantly, such solutions can be cooled to below 200 K without crystallisation (typically forming a glass at lower temperatures) allowing one to explore "no man's land" in detail for the first time. Preliminary experiments combining femtosecond spectroscopy with NMR diffusion measurements have shown that water in these pools undergoes a liquid-liquid transition as predicted for bulk water. Hence, it is proposed to use such nanopools as nanometre scale laboratories for the study of liquid and glassy water. A wide-ranging international collaboration has been set up to be able to study different critical aspects of the structure and dynamics of water. This includes cryogenic viscosity measurements, large dynamic-range (femtosecond to millisecond) optical Kerr-effect experiments, pulsed field gradient NMR, dielectric relaxation spectroscopy, terahertz time-domain spectroscopy, infrared pump-probe spectroscopy, and two-dimensional infrared spectroscopy. To ensure maximum impact of the experimental work, it is critical to have strong ties with experts in the theory and simulation of water and its thermodynamic behaviour. We have arranged collaboration with two international theory groups covering different aspects of the proposed work.Although the proposed research is relatively fundamental in nature, it will have impact as described in more detail elsewhere. The research addresses EPSRC priorities in nanoscience (supramolecular structures in liquids), energy (proton transport and liquid structuring in electrolytes for batteries and fuel cells), life sciences (the role of water in and on biomolecules), and the chemistry-chemical engineering interface (the role of the structuring of water in crystal nucleation). Our strong links with theory collaborators will ensure that fundamental insights will indeed propagate to the 'users' of such information. The close working relationship between the PI and CI has made Glasgow a centre of excellence in advanced femtosecond spectroscopy. This project exploits this expertise and international collaborations to immerse PDRAs and PGRSs in internationally leading research using state-of-the-art previously funded equipment.