Berlin 2015 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 25: Focus session: Structure, chemistry, and ion solvation at solid-liquid interfaces II (joint session O, CPP)

CPP 25.3: Topical Talk

Tuesday, March 17, 2015, 15:00–15:30, HE 101

Synchrotron x-ray determination of ion distributions at liquid interfaces — •Jean Daillant — Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP48, F-91192 Gif sur Yvette Cedex, France

The interfacial behavior of ions is of key importance in a number of phenomena ranging from microfluidics to chemistry in the atmosphere and from protein stability to the transport of pollutants in water.

Beyond Coulombic interaction, the polarisability and hydration of the ions as well as water interfacial structure are important, leading to ion specificity, i.e. possibly dramatically different behavior for ions like Cl⁻ and I⁻. Understanding these effects requires measurements to access the surface composition at the relevant nanometric length-scale.

Investigating the surface composition of alkali-halide aqueous solutions using grazing incidence x-ray fluorescence, differences in concentration over a few angstrom could be resolved, with, for example I⁻ or Br⁻ > Cl⁻. These results could be explained by including a short-range potential accounting for short-range solvent mediated couplings.

Polarization of the liquid-Hg aqueous electrolyte induces extremely large decrease in surface energy with strong ion specificity. Using x-ray reflectivity, we could determine the interfacial structure, demonstrating an accumulation of ions at the Hg surface. Our results challenge the long-standing approximation that assimilates the Hg surface to a smooth, chemically inert surface with a uniform surface charge density.

Finally, using the standing wave technique which allows both high spatial and element sensitivity, we have investigated ion distributions in nano-channels, and I will discuss the first results we have obtained.