Issue 22, 2024

Visualizing partial solvation at the air–water interface

Abstract

Despite significant research, the mechanistic nuances of unusual reactivity at the air–water interface, especially in microdroplets, remain elusive. The likely contributors include electric fields and partial solvation at the interface. To reveal these intricacies, we measure the frequency shift of a well-defined azide vibrational probe at the air–water interface, while independently controlling the surface charge density by introducing surfactants. First, we establish the response of the probe in the bulk and demonstrate that it is sensitive to both electrostatics and hydrogen bonding. From interfacial spectroscopy we infer that the azide is neither fully hydrated nor in a completely aprotic dielectric environment; instead, it experiences an intermediate environment. In the presence of hydrogen bond-accepting sulphate surfactants, competition arises for interfacial water with the azide. However, the dominant influence stems from the electrostatic effect of their negative heads, resulting in a significant blue-shift. Conversely, for the positive ammonium surfactants, our data indicate a balanced interplay between electrostatics and hydrogen bonding, leading to a minimal shift in the probe. Our results demonstrate partial solvation at the interface and highlights that both hydrogen bonding and electrostatics may assist or oppose each other in polarizing a reactant, intermediate, or product at the interface, which is important for understanding and tuning interfacial reactivity.

Graphical abstract: Visualizing partial solvation at the air–water interface

Supplementary files

Article information

Article type
Edge Article
Submitted
25 Feb 2024
Accepted
08 Apr 2024
First published
24 Apr 2024
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2024,15, 8346-8354

Visualizing partial solvation at the air–water interface

K. D. Judd, S. W. Parsons, D. B. Eremin, V. V. Fokin and J. M. Dawlaty, Chem. Sci., 2024, 15, 8346 DOI: 10.1039/D4SC01311E

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