Electric polarizability at solid -liquid interfaces

扫描介电显微镜是一种扫描探针显微镜技术[1]，我们最近开发了探测纳米尺度上的电极化[2，3]。这是物质的基本物理性质，在从物理学到化学和生物学的许多学科中具有重要意义，然而，由于缺乏足够灵敏度的工具，它几乎尚未被探索。特别是，被限制在表面附近或纳米腔中的液体的极化率已知与本体不同。经典的例子是封闭水或界面水，几乎世纪以来，人们一直预测封闭水或界面水的极化率与本体水的极化率不同，但仍不清楚它们的差异有多大。这一点非常重要，因为界面水的极化率决定了水介导的分子间力的强度，而水介导的分子间力又会影响各种现象，包括离子溶剂化、电化学双层结构、离子和分子通过纳米孔的传输、化学反应和大分子组装等。因此，几十年来，界面水的介电性质引起了人们的强烈兴趣，但尚未达成明确的理解。最近，我们成功地将扫描介电显微镜应用于由两个货车德瓦尔斯晶体（石墨和六方氮化硼）制成的二维（2D）纳米狭缝中的水，并发现其偶极极化率受到强烈抑制[4]。该项目将建立在这一开创性的研究和答案的基本问题，所获得的承压水的极端低极化率。例如，这种效应是否取决于表面的化学或某些物理性质？还是纯粹的几何效应？它会随着限制面的形状而改变吗？这些水是如何构成的？为了回答这些问题，学生将使用扫描介电显微镜进行新的实验，学习使用此工具后。这将涉及新的实验数据采集和数据分析。学生将有助于开发新的实验工具和软件，用于扫描介电显微镜，可能需要进行这样的实验。该学生还将为限制分子所需的新2D材料设备的制造做出贡献，例如我们第一项研究中使用的2D纳米缝。为了实现这些目标，学生将接受凝聚态物理小组和曼彻斯特国家石墨烯研究所的主管和其他研究人员的培训。这项研究完全符合EPSRC在物理科学，能源研究和医疗保健方面的战略。特别是，该研究适合分析科学，物理化学和生物化学领域，可以更好地理解涉及界面水的重要物理，生物和化学过程;以及通过帮助理解离子电吸附和传输以及界面处的双电层来理解电化学科学领域。重要的是，这项研究符合EPSRC的重大挑战“理解生命的物理学”，通过研究生命基本分子的关键物理性质，如水，与其独特的溶剂化性质有关。它还符合EPSRC的重大挑战“功能材料的纳米级设计”，通过设计和制造新型2D设备，将液体限制在纳米流体（例如水过滤）和能量存储（例如超级电容器）中急需的新功能中。

Scanning dielectric microscopy is a scanning probe microscopy technique [1] that we have recently developed to probe electric polarizability on the nanoscale [2,3]. This is a fundamental physical property of matter with important implications in many disciplines, from physics to chemistry and biology, and yet, it has remained almost unexplored owing to the lack of tools with sufficient sensitivity. In particular, the polarizability of liquids confined near surfaces or into nanocavities has been known to be different than in bulk. The classical example is that of confined or interfacial water, which for almost one century has been predicted to have different polarizability than that in bulk, and yet how different it remains unclear. This is an extremely important point, as the polarizability of interfacial water determines the strength of water-mediated intermolecular forces, which in turn impacts a variety of phenomena, including ion solvation, the structure of electrochemical double layers, ion and molecular transport through nanopores, chemical reactions and macromolecular assembly, to name but a few. The dielectric properties of interfacial water have therefore attracted intense interest for many decades and, yet, no clear understanding has been reached.Recently we succeeded to apply scanning dielectric microscopy to water confined into two-dimensional (2D) nanoslits made of two van der Waals crystals (graphite and hexagonal boron nitride) and found that its dipolar polarizability is strongly suppressed [4]. This project will build on this groundbreaking study and answer fundamental questions underlying the obtained anomalously low polarizability of confined water. For example, does such effect depend on the chemistry or some physical properties of the surface? Or is it a purely geometric effect? Does it change with the shape of the confining surface? And how such water is actually structured? To answer these questions, the student will carry out new experiments using scanning dielectric microscopy, after learning to use this tool. This will involve new experimental data acquisition and data analysis. The student will contribute to the development of new experimental tools and software for scanning dielectric microscopy that may be needed to carry out such experiments. The student will also contribute to the fabrication of new 2D-materials devices needed to confine the molecules, such as the 2D nanoslits used in our first study. To achieve these objectives, the student will be trained by the supervisor and other research staff of the Condensed Matter Physics group and the National Graphene Institute in Manchester. This research perfectly fits the EPSRC strategies in physical sciences, energy research and health care. In particular, the research fits the areas of analytical science, physical chemistry and biochemistry by allowing better understanding important physical, biological and chemical processes which involve interfacial water; and the areas of electrochemical sciences by helping understanding ion electrosorption and transport and the electric double layer at interfaces. Importantly, this research fits the EPSRC grand challenge 'Understanding the physics of life', by studying a key physical property of a fundamental molecule for life such as water that is related to its unique solvation properties. It also fits the EPSRC grand challenge 'Nanoscale design of functional materials', by designing and fabricating novel 2D devices that confines liquids with new functionalities with much-needed applications in nanofluidics (e,g water filtration) and energy storage (e.g. super-capacitors).