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至少236年来一直困扰着科学，今天仍然被视为化学面临的主要挑战(Whiteside&Deutch，自然，469，21(2011))。有人提出，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。第二个临界点将终止低密度和高密度无定形水相之间的共存线。不幸的是，第二个临界点(如果存在)和相关的多相液-液转变很难研究，因为它被认为低于被称为“无人区”的区域的均匀成核温度(Angell，Science 319,582(2008))。在最近的初步飞秒光学克尔效应实验中，我们已经表明，在浓缩的共晶溶液中的水形成了纳米级的水池，在其中它保留了许多如果不是大部分的大体积液体的特征。最重要的是，这样的溶液可以冷却到200K以下，而不会结晶(通常在较低的温度下形成玻璃)，这使得人们第一次能够详细地探索“无人区”。结合飞秒光谱和核磁共振扩散测量的初步实验表明，这些水池中的水经历了液体-液体转变，就像预测的主体水一样。因此，有人建议将这种纳米孔用作纳米尺度的实验室来研究液态水和玻璃态水。已经建立了一个范围广泛的国际合作，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、脉冲场梯度核磁共振、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方面的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就拟议工作的不同方面进行合作，虽然拟议研究的性质是相对基础的，但它的影响将在其他地方更详细地描述。这项研究涉及EPSRC在纳米科学(液体中的超分子结构)、能量(电池和燃料电池的电解液中的质子传输和液体结构)、生命科学(水在生物分子中和在生物分子上的作用)以及化学-化学工程界面(水的结构在晶体成核中的作用)方面的优先事项。我们与理论合作者的紧密联系将确保基本的洞察力确实会传播到此类信息的“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。该项目利用这种专业知识和国际合作，利用以前资助的最先进的设备，使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.