Electrochemical Waves on Patterned Surfaces: Propagation through Narrow Gaps and Channels

Transient complex oscillations in a closed chemical system with coupled autocatalysis

In this study, hydroquinone was introduced to the classic Belousov-Zhabotinsky (BZ) reaction to build up coupled autocatalytic feedbacks. Various complex dynamical behaviors including successive period-adding bifurcations, irregular oscillations, and frequency modulations were observed in the coupled reaction system. Not only the complexity of oscillations but also the time period during which complex oscillations persist were found to depend greatly on the initial concentration of hydroquinone, which was expected to manifest the coupling strength in the studied system. Dependence of the observed transient complex oscillations on concentrations of ferroin, sulfuric acid, bromate, and malonic acid was also characterized systematically. Numerical simulations with a modified BZ model via incorporating reactions involving hydroquinone and products of hydroquinone qualitatively reproduced the influence of hydroquinone seen in experiments.

Dynamics of excitation pulses with attractive interaction: kinematic analysis and chemical wave experiments

We present a theoretical analysis of stacking and destacking wave trains in excitable reaction-diffusion systems with anomalous velocity-wavelength dependence. For linearized dispersion relations, kinematic analysis yields an analytical function that rigorously describes front trajectories. The corresponding accelerations have exactly one extremum that slowly decays with increasing pulse number. For subsequent pulses these maxima occur with a lag time equal to the inverse slope of the linearized dispersion curve. These findings are reproduced in experiments with chemical waves in the 1,4-cyclohexanedione Belousov-Zhabotinsky reaction but should be also applicable to step bunching on crystal surfaces and certain traffic phenomena.

Traveling fronts of copper deposition

We report the experimental observation of traveling fronts during the electroless deposition of copper on passive steel substrates. The low-carbon steel samples are passivated in nitric acid prior to the plating experiment, thus creating a thin, protective oxide layer on the steel surface. The deposition experiments are carried out from slightly acidic (pH 3.2) copper sulfate solution and copper nitrate solution with the latter showing front propagation only in the presence of chloride ions. For up to 30 s, fronts propagate with constant velocities in the range from 0.5 to 5 mm/s depending on the experimental conditions. This phase of constant-speed propagation gives way to accelerating fronts and very rapid, spatially unstructured deposition. Front-mediated plating is observed over a wide range of cupric ion concentration and constitutes a striking and unexpected example for pattern formation in electrochemical systems.