Front propagation in patterned precipitation. 2. Electric effects in precipitation-dissolution patterning schemes

In this paper, we continue the simulation of periodic precipitation systems with redissolution using the model of Muller and Polezhaev (MP). In the first paper of this sequence (J. Phys. Chem. A 2001, 105, 8053), we proposed a reaction scheme involving precipitation and redissolution to which the MP model was adapted. Maps of Liesegang bands and diffusion profiles were calculated at different concentrations of the inner and outer electrolytes. In this paper, we extend the study to the investigation of the effect of an applied constant electric field on the front propagation. Two reaction schemes, representative of the Co(OH)(2) and Cr(OH)(3) precipitation/redissolution systems, are studied. In the former scheme, the band stratum propagates faster, and the spacing between the bands increases with increasing field strength, exactly reproducing the experimental behavior. In the latter, treated under conditions yielding a single propagating band, two opposing trends are observed: at high field, the propagation is slower at higher field strength, whereas at sufficiently low field, the propagation is enhanced with increasing field strength. Wave stopping occurs at the location reached at the same time in a field-free experiment. This results in the field-on curve crossing the field-free curve at the stopping time, just resembling the experimental observation. Other interesting patterning properties are reported and discussed.