Argonne National Laboratory

Advanced Photon Source
Sector 9

Argonne Home > Advanced Photon Source >

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

126 (5): Art. No. 054704 FEB 7 2007
View Full Text (.pdf)

The surface-normal electron density profile rho(s)(z) of concentrated aqueous salt solutions of RbBr, CsCl, LiBr, RbCl, and SrCl2 was determined by x-ray reflectivity (XR). For all but RbBr and SrCl2 rho(s)(z) increases monotonically with depth z from rho(s)(z)=0 in the vapor (z < 0) to rho(s)(z)=rho(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 similar to 10 angstrom. For SrCl2, the observed rho(s)(z)>rho(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 SrCl2 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.

U.S. Department of Energy UChicago Argonne LLC Office of Science - Department of EnergyOffice of Basic Energy Sciences - Department of Energy
Privacy & Security Notice | Contact Us | Site Map