Electric polarizability at solid -liquid interfaces

扫描介电显微镜是我们最近开发的一种扫描探针显微镜技术[1]，用于探测纳米尺度的电极化率[2，3]。这是物质的一种基本物理性质，在从物理到化学和生物学的许多学科中都有重要影响，但由于缺乏足够灵敏的工具，它几乎没有被探索过。特别是，被限制在表面附近或被限制在纳米腔中的液体的极化率与散体中的液体是不同的。经典的例子是承压水或界面水的极化率，近一个世纪以来，人们一直预测这种水的极化率与散体水的极化率不同，但到底有多大的不同仍不清楚。这是一个极其重要的点，因为界面水的极化率决定了水介导的分子间力的强度，进而影响各种现象，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，仅举几例。因此，界面水的介电性质几十年来一直吸引着人们的浓厚兴趣，但仍然没有明确的认识。最近，我们成功地将扫描介电显微镜应用于由两个van der Waals晶体(石墨和六方氮化硼)组成的二维(2D)纳米狭缝中，发现其偶极极化率被强烈抑制[4]。该项目将建立在这一开创性研究的基础上，并回答导致承压水异常低极化率的根本问题。例如，这种效果是否取决于表面的化学或某些物理性质？或者这是纯粹的几何效果？它是否会随着限制面的形状而变化？这些水实际上是如何构成的？为了回答这些问题，学生将在学习使用该工具后，使用扫描介电显微镜进行新的实验。这将涉及到新的实验数据采集和数据分析。学生将为开发进行此类实验可能需要的扫描介电显微镜的新实验工具和软件做出贡献。这名学生还将参与制造限制分子所需的新的2D材料设备，例如我们第一个研究中使用的2D纳米狭缝。为了实现这些目标，学生将接受曼彻斯特凝聚态物理小组和国家石墨烯研究所的导师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，这项研究有助于更好地了解涉及界面水的重要物理、生物和化学过程，从而适合分析科学、物理化学和生物化学领域；通过帮助了解离子的电吸收和传输以及界面上的双电层，可以更好地了解电化学科学领域。重要的是，这项研究通过研究生命的基本分子的一个关键物理属性，如与其独特的溶剂化属性相关的水，符合EPSRC的重大挑战--理解生命的物理学。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设备来限制具有新功能的液体，这些液体在纳米流体(例如水过滤)和能量存储(例如超级电容器)中具有迫切需要的应用。

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).