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Succinic acid in aqueous solution: connecting microscopic surface composition and macroscopic surface tension
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
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2014 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 39, 21486-21495 p.Article in journal (Refereed) Published
Abstract [en]

The water vapor interface of aqueous solutions of succinic acid, where pH values and bulk concentrations were varied, has been studied using surface sensitive X-ray photoelectron spectroscopy (XPS) and molecular dynamics (MD) simulations. It was found that succinic acid has a considerably higher propensity to reside in the aqueous surface region than its deprotonated form, which is effectively depleted from the surface due to the two strongly hydrated carboxylate groups. From both XPS experiments and MD simulations a strongly increased concentration of the acid form in the surface region compared to the bulk concentration was found and quantified. Detailed analysis of the surface of succinic acid solutions at different bulk concentrations led to the conclusion that succinic acid saturates the aqueous surface at high bulk concentrations. With the aid of MD simulations the thickness of the surface layer could be estimated, which enabled the quantification of surface concentration of succinic acid as a multiple of the known bulk concentration. The obtained enrichment factors were successfully used to model the surface tension of these binary aqueous solutions using two different models that account for the surface enrichment. This underlines the close correlation of increased concentration at the surface relative to the bulk and reduced surface tension of aqueous solutions of succinic acid. The results of this study shed light on the microscopic origin of surface tension, a macroscopic property. Furthermore, the impact of the results from this study on atmospheric modeling is discussed.

Place, publisher, year, edition, pages
2014. Vol. 16, no 39, 21486-21495 p.
National Category
Chemical Sciences
URN: urn:nbn:se:uu:diva-236531DOI: 10.1039/c4cp02776kISI: 000343072900050PubMedID: 25182698OAI: oai:DiVA.org:uu-236531DiVA: diva2:766361
Available from: 2014-11-26 Created: 2014-11-19 Last updated: 2016-01-13Bibliographically approved
In thesis
1. Exploring the Surface of Aqueous Solutions: X-ray photoelectron spectroscopy studies using a liquid micro-jet
Open this publication in new window or tab >>Exploring the Surface of Aqueous Solutions: X-ray photoelectron spectroscopy studies using a liquid micro-jet
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The surface behavior of biologically or atmospherically relevant chemical compounds in aqueous solution has been studied using surface-sensitive X-ray photoelectron spectroscopy (XPS). The aim is to provide information on the molecular-scale composition and distribution of solutes in the surface region of aqueous solutions. In the first part, the distribution of solutes in the surface region is discussed, where in particular single molecular species are studied. Concentration-dependent studies on succinic acid and various alkyl-alcohols, where also parameters such as pH and branching are varied, are analyzed using different approaches that allow the quantification of surface concentrations. Furthermore, due to the sensitivity of XPS to the chemical state, reorientation of linear and branched alkyl-alcohols at the aqueous surface as a function of concentration is observed. The results are further discussed in terms of hydrophilic and hydrophobic interactions in the interfacial region, where the three-dimensional hydrogen bonded water structure terminates. In the second part, mixed solutions of compounds, both ionic and molecular, are inspected. Again concentration, but also co-dissolution of other chemical compounds, are varied and differences in the spatial distribution and composition of the surface region are discussed. It is found that the guanidinium ion has an increased propensity to reside at the surface, which is explained by strong hydration in only two dimensions and only weak interactions between the aromatic π-system and water. Ammonium ions, on the other hand, which require hydration in three dimensions, are depleted from the surface region. The presence of strongly hydrated electrolytes out-competes neutral molecules for hydrating water molecules leading to an enhanced abundance of molecules, such as succinic acid, in the interfacial region. The partitioning is quantified and discussed in the context of atmospheric science, where the impact of the presented results on organic loading of aerosol particles is emphasized.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 88 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1313
X-ray Photoelectron spectroscopy, liquid micro-jet, air-water interface, inorganic salt, carboxylic acid, alcohol, isomers, hydration.
National Category
Atom and Molecular Physics and Optics Condensed Matter Physics Chemical Sciences
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
urn:nbn:se:uu:diva-265210 (URN)978-91-554-9399-8 (ISBN)
Public defence
2015-12-18, Häggsalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Available from: 2015-11-27 Created: 2015-10-25 Last updated: 2016-01-13

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