The way ions arrange themselves alongside a polarized interface is crucial to the functioning of many systems, from biological membranes to manmade nanodevices.  As the predictions of a classical theory addressing this issue seemed to agree well with observations only at the limit of low ion concentration, a new model, taking into account ion-solvent interactions and ion-ion correlations have been developed by researchers from the University of Illinois at Chicago, Northern Illinois University, the University of Chicago, and the University of California, Santa Cruz.  Testing the new model required the ability to measure ion concentrations near the interface, with sub-nanometer spatial resolution.  The measurements were performed using high energy (30keV) x-rays, at the 15‑IDC Liquid Surface Scattering station at the APS that is currently the only facility in the US capable of providing the required combination of beam energy and spatial resolution.

See: Nouamane Laanait1, Miroslav Mihaylov1, Binyang Hou1, Hao Yu1, Petr Vanýsek2, Mati Meron3, Binhua Lin3, Ilan Benjamin4, and Mark L. Schlossman1**, “Tuning ion correlations at an electrified soft interface,” Proc. natl. Acad. Sci. USA 109, 20326 (2012). Doi:10.1073/pnas.1214204109 Author affiliations: 1University of Illinois at Chicago; 2Northern Illinois university; 3the University of Chicago; 4University of California, Santa Cruz Correspondence: **

Also See: “Profiling Border Ions”, Page 56 in “APS Science 2012”,