Investigation of water evaporation process at air/water interface using Hofmeister ions

Rana, B., Fairhurst, D.J. ORCID: 0000-0001-5311-0762 and Jena, K.C., 2022. Investigation of water evaporation process at air/water interface using Hofmeister ions. Journal of the American Chemical Society, 144 (39), pp. 17832-17840. ISSN 0002-7863

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Evaporation is an interfacial phenomenon in which a water molecule breaks the intermolecular hydrogen (H-) bonds and enters the vapor phase. However, a detailed demonstration of the role of interfacial water structure in the evaporation process is still lacking. Here, we purposefully perturb the H-bonding environment at the air/water interface by introducing kosmotropic (HPO_4^(-2), SO_4^(-2), and CO_3^(-2)) and chaotropic ions (NO_3^- and I^-) to influence the evaporation process. Using time-resolved interferometry on aqueous salt-droplets, we found that kosmotropes reduce evaporation, whereas chaotropes accelerate the evaporation process, following the Hofmeister series HPO_4^(-2)< SO_4^(-2)<CO_3^(-2)< Cl^-<NO_3^-< I^-. In order to extract deeper molecular level insights about the observed Hofmeister trend in the evaporation rates, we investigated the air/water interface in the presence of ions using surface-specific sum frequency generation (SFG) vibrational spectroscopy. The SFG vibrational spectra reveal the significant impact of ions on the strength of the H-bonding environment and on the orientation of free OH oscillators at the air/water interface, where both affects follow the Hofmeister series. It is established that in the presence of kosmotropes the slow evaporating water molecules experience a strong H-bonding environment with the free OH oscillators tilted away from the surface normal. In contrast, the fast evaporating water molecules in the presence of chaotropes experience a weak H-bonding environment with free OH oscillators tilted towards the surface normal at the air/aqueous interface. Our experimental outcomes showcase the complex bonding environment of interfacial water molecules and their decisive role in evaporation at the air/water interface.

Item Type: Journal article
Publication Title: Journal of the American Chemical Society
Creators: Rana, B., Fairhurst, D.J. and Jena, K.C.
Publisher: American Chemical Society (ACS)
Date: 5 October 2022
Volume: 144
Number: 39
ISSN: 0002-7863
Divisions: Schools > School of Science and Technology
Record created by: Jeremy Silvester
Date Added: 10 Nov 2022 09:21
Last Modified: 22 Sep 2023 03:00

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