ABSTRACT
Abstract Impedance of membrane systems is considered within a wide frequency range. Two types of impedance dispersion are discussed to be predictable in frame of the phenomenological approaches. They are the Maxwell and the low-frequency dispersion attributed to the substantially different frequency ranges, however. Classic results concerned with Maxwell's dis-
persion type are stated as applied to a multilayer membrane characterized by specific conductivities and permittivities of the constituent layers. The restrictions of a phenomenological approach are discussed to single out those membranes in which a sole macroscopic electrodynamics description is possible. A new theoretical approach based on the irreversible thermodynamics is proposed in order to describe the low-frequency dispersion. The property of a medium to accumulate a substance is described in the theory by introducing a special thermostatic coefficient. It is referred to as the chemical capacity being the proportionality coefficient between the amount of the substance accumulated and the change of the chemical potential. The chemical capacity is applied to various models of the media showing that its magnitude substantially depends on the medium sorption properties. In the general problem formulation the chemical capacity is set for each constituent phase as a phenomenological coefficient. The approach enables one to predict the impedance response in purely phenomenological characteristics of the constituent parts of the membrane system. No model of the charge carrier transport is used in the theory. Impedance of both an elementary membrane cell and a multilayer membrane is predicted by using the new approach. Theoretical results presented in literature are shown to be particular cases of the theoretical predictions. Equivalent electric circuits are proposed to simulate impedance behavior. Some methods of data interpretation in impedance spectroscopy are suggested. Experimental data from the literature are analyzed to obtain the chemical capacity of the membranes under consideration. It is shown which conclusions can be made by dealing with the chemical capacity as a function of some parameters.
