Dresden 2026 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 23: Focus Session: Water – from Atmosphere to Space II (joint session CPP/DY)

CPP 23.3: Talk

Tuesday, March 10, 2026, 11:45–12:00, ZEU/LICH

Ion Correlations Drive Collective Adsorption of Hydronium Ions at the Air-Electrolyte Interface — •Elena Köhler Ruiz, Maximilian Becker, Louis Lehmann, and Roland Netz — Fachbereich Physik, Freie Universität Berlin, Germany

Acids exhibit distinct interfacial behavior at the air-water interface compared to simple monoatomic salts. While monoatomic ions are largely repelled from the interface, hydronium ions preferentially reside at the interface due to formation of an interfacial hydrogen-bond network. To investigate these contrasting behaviors, we perform molecular-dynamics simulations with thermodynamically optimized force fields, analyzing ionic distributions at the interface as well as resulting surface tensions and potentials. The simulated surface potentials reproduce the concentration-dependent trends observed in SFG experiments: At high concentrations, interfacial hydronium promotes co-adsorption of counterions, which results in a decrease of the surface potential with rising concentration, consistent with experimental observations. These findings highlight the critical role of ion-ion correlations at interfaces, which are not accounted for by modified Poisson-Boltzmann models.

Keywords: Interfacial Adsorption; Hydronium Ions; Ion-Ion Correlations; SFG Spectroscopy; Molecular Dynamics Simulations