SKM 2023 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 44: Wetting, Fluidics and Liquids at Interfaces and Surfaces II (joint session CPP/DY)

CPP 44.9: Talk

Thursday, March 30, 2023, 11:45–12:00, MER 02

Electrokinetic, electrochemical and electrostatic surface potentials of the pristine water liquid-vapor interface — •Maximilian R Becker and Roland R Netz — Freie Universität Berlin, Berlin, Germany

Although conceptually simple, the interface between liquid water and vapor displays rich behavior and is subject to intense experimental and theoretical investigations. Different definitions of the electrostatic surface potential as well as different calculation methods, each relevant for distinct experimental scenarios, lead to widely varying potential magnitudes. Here, based on density-functional-theory (DFT) molecular dynamics (MD) simulations, different surface potentials are evaluated and compared to force-field (FF) MD simulations. The laterally averaged electrostatic surface potential, accessible to electron holography, is dominated by the trace of the water molecular quadrupole moment and therefore differs strongly between DFT and FF MD. Thus, when predicting electrostatic potentials within water molecules DFT simulation methods need to be used. The electrochemical surface potential inside a neutral atom, relevant for ion transfer reactions and ion surface adsorption, is much smaller and depends specifically on the atom radius. Charge transfer between interfacial water molecules leads to a sizable surface potential as well. However, when probing electrokinetics by explicitly applying a lateral electric field in DFT-MD simulations, the electrokinetic zeta-potential turns out to be negligible. Thus, interfacial polarization charges from charge transfer between water molecules do not lead to a significant electrokinetic mobility.