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Research article2015Peer reviewedOpen access

Surface behavior of amphiphiles in aqueous solution: a comparison between different pentanol isomers

Walz, Marie-Madeleine; Caleman, C.; Werner, Josephina; Ekholm, Victor; Lundberg, Daniel; Prisle, Nønne; Öhrwall, Gunnar; Björneholm, Olle; Öhrwall, Gunnar

Abstract

Position isomerism is ubiquitous in atmospheric oxidation reactions. Therefore, we have compared surface-active oxygenated amphiphilic isomers (1- and 3-pentanol) at the aqueous surface with surface- and chemically sensitive X-ray photoelectron spectroscopy (XPS), which reveals information about the surface structure on a molecular level. The experimental data are complemented with molecular dynamics (MD) simulations. A concentration-dependent orientation and solvation of the amphiphiles at the aqueous surface is observed. At bulk concentrations as low as around 100 mM, a monolayer starts to form for both isomers, with the hydroxyl groups pointing towards the bulk water and the alkyl chains pointing towards the vacuum. The monolayer (ML) packing density of 3-pentanol is approx. 70% of the one observed for 1-pentanol, with a molar surface concentration that is approx. 90 times higher than the bulk concentration for both molecules. The molecular area at ML coverage (approximate to 100 mM) was calculated to be around 32 +/- 2 Å2 per molecule for 1-pentanol and around 46 +/- 2 Å2 per molecule for 3-pentanol, which results in a higher surface concentration (molecules per cm2) for the linear isomer. In general we conclude therefore that isomers - with comparable surface activities - that have smaller molecular areas will be more abundant at the interface in comparison to isomers with larger molecular areas, which might be of crucial importance for the understanding of key properties of aerosols, such as evaporation and uptake capabilities as well as their reactivity.

Published in

Physical Chemistry Chemical Physics
2015, volume: 17, number: 21, pages: 14036-14044
Publisher: ROYAL SOC CHEMISTRY

SLU Authors

  • Werner, Josephina

    • The Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences

  • Lundberg, Daniel

    • The Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences

UKÄ Subject classification

Atom and Molecular Physics and Optics
Organic Chemistry

Publication identifier

  • DOI: https://doi.org/10.1039/c5cp01870f

Permanent link to this page (URI)

https://res.slu.se/id/publ/67459