Dielectric Properties of Water under Atomic-Scale Confinement and at Interfaces

Water’s dielectric polarization near interfaces and under atomic-scale confinement governs molecular interactions, solvation, transport, and chemical reactivity, yet has been notoriously difficult to measure due to the lack of tools with sufficient sensitivity. I will present our recent experimental advances that directly probe and quantify the dielectric — and conductive — properties of near-surface and strongly confined water on the atomic scale using advanced scanning-probe platforms. After a brief methods overview [1-3], I will discuss spatially resolved results for few-layer water adjacent to biological interfaces [4] and under strong confinement inside nanocapillaries made by van der Waals crystals assembly [5-7], with particular emphasis on our latest in-plane measurements [7]. Our experiments show that interfacial and nanoconfined water exhibits dielectric and conductive properties that greatly differ from those of bulk water. These local, quantitative measurements open new avenues for understanding physical and biochemical processes, and provide important feedback for theories describing water and water-mediated interactions.