Electric polarizability at solid -liquid interfaces

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).