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O: Fachverband Oberflächenphysik

O 28: Solid-Liquid Interfaces II: Structure and Spectroscopy

O 28.3: Talk

Tuesday, March 19, 2024, 11:00–11:15, H 1012

Depth-Resolved SFG/DFG Spectroscopy of Charged Aqueous Interfaces — •Álvaro Díaz Duque, Alexander Fellows, Martin Wolf, and Martin Thämer — Fritz Haber Institut der MPG, Berlin, Germany

Charged aqueous interfaces are omnipresent in our world, being a crucial ingredient on both natural systems and technical devices. The charges at such interfaces generate electric fields which interact with the electrolyte and can extend over relatively large length scales. The evolution of the potential in such systems is typically described by the Gouy-Chapman-Stern (GCS) theory. However, much less in known about the depth-dependent structural properties of the main constituent of the electrolyte, the water.

Vibrational Sum-frequency generation spectroscopy is commonly used to study aqueous interfaces. The particular strength of this technique is its sensitivity to structural anisotropy and its ability to report on the molecular orientation and intermolecular environment of water. Here, we utilize our recent development that combines phase-resolved SFG and DFG which additionally yields depth resolution on the nm scale. We study the details of the depth-dependent water structure within the electric double layer and correlate these to the defining thermodynamic and electrostatic quantities in the investigated electrolyte. Based on the results we demonstrate that the continuum solvent model that is typically assumed within the GCS theory is clearly insufficient to accurately describe water in such systems.

Keywords: SFG/DFG; Charged Liquid Interfaces; Nonlinear Spectroscopy