Friday, July 12, 2013

1307.3090 (Andreas Reindl et al.)

Impedance spectroscopy of ions at liquid-liquid interfaces    [PDF]

Andreas Reindl, Markus Bier
The possibility to extract properties of an interface between two immiscible electrolyte solutions (ITIES) by means of impedance spectroscopy is investigated theoretically within a dynamic density functional theory which is equivalent to the Nernst-Planck-Poisson theory. A novel approach based on a two-step fitting procedure of an equivalent circuit to impedance spectra is proposed which avoids overfitting of the bulk properties of the two liquids in contact and underfitting of the interfacial properties, as they might occur for standard one-step procedures. The key idea is to determine the bulk elements of the equivalent circuit in a first step by fitting corresponding sub-circuits to the spectra of uniform electrolyte solutions, and afterwards fitting the full equivalent circuit with fixed bulk elements to the impedance spectrum of the ITIES. This approach is exemplified for an equivalent circuit which leads to a physically intuitive qualitative behavior as well as to quantitively realistic values of the interfacial elements. The proposed method is robust such that it can be expected to be applicable to a wide class of systems with liquid-liquid interfaces.
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