Sonderseminar SFB 985:
Electric impedance, admittance and dielectric permittivity of charged gels and membranes:
A phenomenological approach
Prof. Dr. Emiliy K Zholkovskyy
Institute of Bio-Colloid Chemistry of National Academy of Sciences of Ukraine
- 02 May 2017 10:30
- 02 May 2017 11:30
- Seminarraum A1-3, Building 04.6, Entrance E1
A passage of AC electric current is analyzed through a charged gel (or membrane), considered as a heterogeneous ionic conductor composed of several homogeneous conducting phases. The transitions between the constituent phases are assumed to be vanishingly thin. Each of the homogeneous phases is described in a phenomenological way, i.e., without assumptions about specific mechanisms of ion transfer. Instead, each of the phases is characterized by a set of phenomnological coefficients: dielectric permittivity; electric conductivity, Hittorf transport numbers for individual ions and a thermostatic coefficient which is referred to as the chemical capacity. The latter coefficient characterizes the changes in the binary electrolyte chemical potential while changing its concentration within the respective constituent phase.
For different geometries of the heterogeneous system under consideration, the electric immittance is calculated as a function of applied frequency. Two frequency ranges of the immittance dispersion are indicated. The high-frequency and so-called Maxwell-Wagner dispersion occurs due to the finite rate of formatting the interfacial electric charge which forms when the electric current crosses an interface between two media with different conductivities and permittivities. The low-frequency dispersion occurs due to redistribution of ions in the bulk phase. The latter effect is observed when the electric current crosses the interface between two media having different Hittorf transport numbers attributed to the same ions. The obtained expressions for impedance, admittance and dielectric permittivity as functions of applied frequency are discussed. In particular, it is discussed how one obtains information about the gel or membrane morphology from the immittance spectra.
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