The surface structure of concentrated aqueous salt solutions

E. Sloutskin, J. Baumert, B. M. Ocko, I. Kuzmenko, A. Checco, L. Tamam, E. Ofer, T. Gog, O. Gang, M. Deutsch

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Abstract

The surface-normal electron density profile ρ s (z) of concentrated aqueous salt solutions of RbBr, CsCl, LiBr, RbCl, and Sr Cl2 was determined by x-ray reflectivity (XR). For all but RbBr and Sr Cl2 ρ s (z) increases monotonically with depth z from ρ s (z) =0 in the vapor (z<0) to ρ s (z) = ρ b of the bulk (z>0) over a width of a few angstroms. The width is commensurate with the expected interface broadening by thermally excited capillary waves. Anomalous (resonant) XR of RbBr reveals a depletion at the surface of Br- ions to a depth of ∼10 Å. For Sr Cl2, the observed ρ s (z) > ρ b may imply a similar surface depletion of Cl- ions to a depth of a few angstorms. However, as the deviations of the XRs of RbBr and Sr Cl2 from those of the other solutions are small, the evidence for a different ion composition in the surface and the bulk is not strongly conclusive. Overall, these results contrast earlier theoretical and simulational results and nonstructural measurements, where significant surface layering of alternate, oppositely charged, ions is concluded.

Original languageEnglish
Article number054704
JournalJournal of Chemical Physics
Volume126
Issue number5
DOIs
StatePublished - 7 Feb 2007

Bibliographical note

Funding Information:
The authors thank Yuguang Cai (BNL) for assistance and discussions. BNL is supported by U.S. DOE Contract No. DE-AC02-98CH10886. CMC-CAT is supported by OBES, U.S. DOE, and by NSF, Division of Materials Research. The APS is supported by U.S. DOE Contract No. W-31-109-Eng-38. Support by the U.S.-Israel Binational Science Foundation, Jerusalem, is gratefully acknowledged.

Funding

The authors thank Yuguang Cai (BNL) for assistance and discussions. BNL is supported by U.S. DOE Contract No. DE-AC02-98CH10886. CMC-CAT is supported by OBES, U.S. DOE, and by NSF, Division of Materials Research. The APS is supported by U.S. DOE Contract No. W-31-109-Eng-38. Support by the U.S.-Israel Binational Science Foundation, Jerusalem, is gratefully acknowledged.

FundersFunder number
OBES
National Science Foundation
U.S. Department of EnergyDE-AC02-98CH10886
Division of Materials ResearchW-31-109-Eng-38
United States-Israel Binational Science Foundation

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