Friday, July 22, 2011, 12:00 pm — Seminar Room, Bldg. 725
An important unsolved problem in the study of ion distributions is the relationship of macroscopic electrochemistry measurements to the ion distribution determined by microscopic synchrotron x-ray scattering measurements. In this work, we present recent x-ray reflectivity and interfacial tension measurements of electrified oil/water interfaces as a function of interfacial electric potential for a series of interfaces between solutions of 10 mM alkali chloride (XCl, where X is the alkali metal ion of Li+, Na+, Rb+ and Cs+) in water and 5 mM organic supporting electrolyte BTPPATPFB in 1, 2-dichloroethane (DCE). The potential is established by the use of electrodes and supporting electrolytes in the bulk phases.
Interfacial tension as a function of interfacial electric potential was measured to determine the potential of zero charge (PZC) and the capillary wave roughness of each interface. The interfacial excess charge was determined from the tension measurements as well.
X-ray scattering experiments were carried out at the ChemMatCARS beamline 15-ID at the Advanced Photon Source (Argonne National Laboratory, USA). Large changes in reflectivity occur from intermediate potentials for each sample. These results disagree with predictions of the Gouy-Chapman (GC) theory. A Poisson-Boltzmann (PB) calculation that incorporates a potential of mean force (PMF) to describe the role of liquid structure on the ion distributions agrees well with the x-ray reflectivity data. These results confirmed a layer of TPFB- ion formed at the interfaces at high positive electric potentials.
In addition, we calculated the excess interfacial charge from the ion distributions determined by the x-ray measurements analysis for each interface. These calculated excess interfacial charges from the PB-PMF method are in good agreement with the tension measurement results. These agreements make a direct connection between the molecular level x-ray measurements and macroscopic interfacial tensi
Hosted by: Lin Yang
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