Nonlinear behaviour of simple ionic systems in hydrogel in an electric field

Abstract

The stationary behavior of ionic reaction–transport systems contained in hydrogel located between two reservoirs of electrolytes is investigated. The effects of the applied voltage, the composition of the electrolytes in the reservoirs and the distribution of fixed charge in the hydrogel on the spatial patterns of charge, electric potential, temperature and concentrations of the individual components are studied systematically by mathematical modelling. Such systems, containing only several ions (for example, Cl⁻, K⁺, OH⁻ and H⁺) can function as electrolyte diodes and transistors and can exhibit oscillations and hysteresis. The mathematical description of the studied systems is based on balances of species, enthalpy and charge, on Poisson's equation and on the finite rate description of the water dissociation/recombination reaction, without assuming local electroneutrality. The modeling results are compared with experiments, including the system with hydrogel connecting reservoirs of strong base and acid studied by Noszticzius and co-workers. [L. H. Hegedus, N. Kirschner, M. Wittmann and Z. Noszticzius, J. Phys. Chem. A, 1998, 102, 6491 (ref. 1); L. H. Hegedus, N. Kirschner, M. Wittmann, P. Simon and Z. Noszticzius, Chaos, 1999, 9, 283 (ref. 2).]