Seminar by Arnaldo Naves de Brito: "Electron Spectroscopy: Providing Molecular Scale Information on the Surface and Bulk of Ethanol-Water Liquid Mixtures"

Electron Spectroscopy: Providing Molecular Scale Information on the Surface and Bulk of Ethanol-Water Liquid Mixtures

Arnaldo Naves de Brito, Department of Applied Physics, University of Campinas, Campinas, Brazil arnaldo@ifi.unicamp.br

Abstract

In this talk, I present cylindrical micro-jet photoelectron spectroscopy (cMJ-PES) and theoretical simulations to study the properties of ethanol-water solutions at different concentrations1, from 0 to 100 Mol % ethanol. The aim is to better understand the microscopic structure and intermolecular bonding patterns of these mixtures. While ethanol-water solutions are widely used and studied, there is still controversy over the nature of their hydrogen bonding networks. We found that ethanol molecules form a film on the surface at low concentrations, making it energetically favorable2. In bulk, up to 10 Mol %, ethanol, and oxygen atoms tend to form a third acceptor hydrogen bond to water molecules. At 20 Mol %, we have results pointing out the presence of clathrate structures. Ethanol forms a closely packed layer at the surface between 5-25 Mol %. Above 85 Mol %, we have evidence that water tends to move to the surface, which explains the azeotrope effect3. I compare our findings with other spectroscopic techniques and highlight the importance of combining molecular dynamics with quantum predictions for cMJ-PES measurements4. Our protocol can be applied to studying other alcohol mixtures and binary solutions.

References

1. Ågren, H.; Björneholm, O.; Öhrwall, G.; Carravetta, V.; de Brito, A. N. Ethanol in Aqueous Solution Studied by Microjet Photoelectron Spectroscopy and Theory. Acc. Chem. Res. 2022, 55, 3080-3087.
2. Marinho, R. R. T.; Walz, M.-M.; Ekholm, V.; Öhrwall, G.; Björneholm, O.; Naves de Brito, A. Ethanol Solvation in Water Studied on a Molecular Scale by Photoelectron Spectroscopy. J. Phys. Chem. B 2017, 121, 7916.
3. Carravetta, V.; Gomes, A. H. d. A.; Marinho, R. d. R. T.; Öhrwall, G.; Ågren, H.; Björneholm, O.; de Brito, A. N. An Atomistic Explanation of the Ethanol–Water Azeotrope. Phys. Chem. Chem. Phys. 2022, 24, 26037-26045.
4. Kirschner, J.; Gomes, A. H. A.; Marinho, R. R. T.; Björneholm, O.; Ågren, H.; Carravetta, V.; Ottosson, N.; Brito, A. N. d.; Bakker, H. J. The Molecular Structure of the Surface of Water–Ethanol Mixtures. Phys. Chem. Chem. Phys. 2021, 23, 11568-11578.