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Strong Enrichment of Atmospherically Relevant Organic Ions at the Aqueous Interface: The Role of Ion Pairing and Cooperative Effects
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. DESY, Ctr Free Elec Laser Sci, Notkestr 85, DE-22607 Hamburg, Germany.
Royal Inst Tech, Dept App Phys, Roslagstullsbacken 21, SE-11421 Stockholm, Sweden.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Computational Biology and Bioinformatics.
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2018 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 42, p. 27185-27191Article in journal (Refereed) Published
Abstract [en]

Surface affinity, orientation and ion pairing are investigated in mixed and single solute systems of aqueous sodium hexanoate and hexylammonium chloride. The surface sensitive X-ray photoelectron spectroscopy technique has been used to acquire the experimental results, while the computational data have been calculated using molecular dynamics simulations. By comparing the single solute solutions with the mixed one, we observe a non-linear surface enrichment and reorientation of the organic ions with their alkyl chains pointing out of the aqueous surface. We ascribe this effect to ion paring between the charged functional groups on the respective organic ion and hydrophobic expulsion of the alkyl chains from the surface in combination with van der Waals interactions between the alkyl chains. These cooperative effects lead to a substantial surface enrichment of organic ions, with consequences for aerosol surface properties.

Place, publisher, year, edition, pages
2018. Vol. 20, no 42, p. 27185-27191
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:uu:diva-357368DOI: 10.1039/c8cp04525aISI: 000451351500042PubMedID: 30339167OAI: oai:DiVA.org:uu-357368DiVA, id: diva2:1239170
Funder
Swedish Research Council, 2013-3940Swedish Research Council, 2014-04518Carl Tryggers foundation Available from: 2018-08-15 Created: 2018-08-15 Last updated: 2019-01-07Bibliographically approved
In thesis
1. Ion pairing and Langmuir-like adsorption at aqueous surfaces studied by core-level spectroscopy
Open this publication in new window or tab >>Ion pairing and Langmuir-like adsorption at aqueous surfaces studied by core-level spectroscopy
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Surface-bulk equilibria for solutes in aqueous solutions are studied using X-ray Photoelectron Spectroscopy (XPS) with high surface and chemical sensitivity. In the first part, the results show a reduction of the biochemically relevant guanidinium ions’ surface propensity with the addition of disodium sulphate due to ion pairing with the strongly hydrated sulphate ion, which could have implications for protein folding. Thereafter, the work considers amphiphilic organic compounds related to atmospheric science where the surface propensities, orientations at the surface and solute-solute and solute-solvent interactions are investigated. In the second part, two linear organic ions are investigated both as single solutes and in mixture. Both organic ions are surface enriched on their own and even more in the mixed solute solution. Due to hydrophobic expulsion of the alkyl chains, ion pairing between the organic ions and van der Waals interaction, the organic ions seem to assemble in clusters with their alkyl chains pointing out of the surface. The third part also covers linear organic compounds but one at a time probing the surface concentration as a function of bulk concentration. A Langmuir-like adsorption behavior was observed and Gibb’s free energy of surface adsorption (ΔGAds) values were extracted. An empiric model for deriving values for ΔGAds is proposed based upon the seemingly linear change in ΔGAds per carbon when comparing alcohols of different chain lengths. The fourth part investigates the acid/base fraction at the surface as function of bulk pH. The most important factor for this fraction seems to be how the surface propensity varies with the charge state of the acid or base instead of a possible difference in pH or pKa value at the surface. In the fifth part the oxygen K-edge of aqueous carbonate and bicarbonate is probed with the bulk-sensitive Resonant Inelastic X-ray Scattering (RIXS) technique.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 62
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1715
Keywords
XPS, Surface, Aqueous, Liquid jet, Langmuir
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-357369 (URN)978-91-513-0432-8 (ISBN)
Public defence
2018-10-19, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
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Supervisors
Available from: 2018-09-27 Created: 2018-09-02 Last updated: 2018-10-16

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