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Seminar by Alper Tunga CELEBI (Institute of Applied Physics, Technische Universitat Wien, Austria)

Abstract:The key mechanisms governing the processes at solid-liquid interfaces remain largely elusive, and requires atomic-level understanding of the interfacial structure, dynamics, chemical composition, thermodynamics and charge distribution. While continuum theories are often used to model solid–liquid interfaces, they tend to break down at molecular scales. At the same time, the resolution of many experimental techniques usually lacks the spatial resolution needed to fully capture and interpret nanoscale interfacial changes. To bridge this gap, we employ molecular simulations that provide detailed insights and complement experimental measurements and theoretical approaches. In this seminar, we present a series of case studies on solid–liquid interfacial phenomena, including ion adsorption, hydration, electric double layer (EDL) formation, and ion/liquid transport; all explored through density functional theory and molecular dynamics simulations. Our simulations demonstrate a certain ion-specificity towards the adsorption and hydration, primarily attributed to the ionic properties (e.g., hydration shell, size, valency, etc.) and surface features (e.g., surface chemistry, charge density), resulting in an overscreening and underscreening phenomena. This is complemented by high-resolution atomic force microscopy imaging at mica interfaces, which resolves the crystal structure of the mica surface immersed in aqueous solution and adsorbed ions from the salt-rich solutions at different concentrations. Furthermore, we demonstrate that the solution chemistry is a critical factor tuning the surface properties. With an increased pH of electrolyte solution, an enhanced deprotonation of the silanol groups of silica surface is observed which increase the net negative surface charge. This effectively restructures the EDL, and subsequently affecting both ion adsorption and electrokinetic transport. Using surface force apparatus measurements backed by molecular simulations, we capture real-time transport processes of ionic species in electrochemically modulated and molecularly confined gold surfaces. Overall, such atomistic understanding of solid–liquid interfaces is essential to unravelling many natural phenomena and a wide range of technological applications. For instance, surface charge regulated membranes can enable high ion selectivity, and effective flow control for desalination and electrochemical energy storage systems.