A modular approach to self-oscillating polymer systems driven by the Belousov–Zhabotinsky reaction

This review explores the principle, modular construction, integral control and engineering aspects of self-oscillating polymer systems driven by the Belousov–Zhabotinsky reaction.

HOI versus HOIO selectivity of a molten-type AgI electrode

AgI electrode is often applied not only to determine iodine concentration but also to follow oscillations in the weakly acidic medium of the Bray-Liebhafsky and Briggs-Rauscher reactions where it partly follows the hypoiodous acid (HOI) concentration. It is known that HOI attacks its matrix in the corrosion reaction: AgI + HOI + H(+) ⇆ Ag(+) + I2 + H2O and the AgI electrode measures the silver ion concentration produced in that reaction. The signal of the electrode can be the basis of sensitive and selective HOI concentration measurements only supposing that an analogous corrosive reaction between AgI and iodous acid (HOIO) can be neglected. To prove that assumption, the authors calibrated a molten-type AgI electrode for I(-), Ag(+), HOI, and HOIO in 1 M sulfuric acid and measured the electrode potential in the disproportionation of HOIO, which is relatively slow in that medium. Measured and simulated electrode potential versus time diagrams showed good agreement, assuming that the electrode potential is determined by the HOI concentration exclusively and the contribution of HOIO is negligible. An independent and more direct experiment was also performed giving the same result. HOIO was produced with a new improved recipe.

CONCLUSION

an AgI electrode can be applied to measure the HOI concentration selectively above the so-called solubility limit potential.

Reexamination of gas production in the Bray-Liebhafsky reaction: what happened to O2 pulses?

Results of high-precision measurements of gas production in the BL reaction are presented, and an efficient kinetic model for their analysis is proposed. Based on this model, the data have been examined pulse by pulse, and for the first time, the entire records of gas production could be successfully reduced to series of just a few key parameters. It has been confirmed that the kinetics of O2(g) production is of the first order with respect to its precursor. Overall, only two steps have been found necessary to fit the observed pulses in gas production. The first step produces the precursor of the recorded O2(g), and its rate has two components. One component provides the peaks, and its approximation in the form of Gaussian functions has been found as satisfactory. The other component provides the constant baseline of gas production between the pulses. Finally, the precursor gives rise to O2(g) in the second step, and the simple first-order kinetics suggests that the precursor is otherwise relatively unreactive, making O2(aq) a logical candidate. However, the rate constant of this process showed almost perfect linearity with the actual concentrations of H2O2, and it was affected only little by variations in the rate of stirring. It thus seems possible that this final step in gas production, responsible for the majority of O2 produced in pulses, might not be the interphase transport O2(aq) → O2(g), as expected. Instead, it might be a truly chemical process, giving rise to O2(g) in a reaction of H2O2 with another precursor, which is not involved significantly in any other process, but it is not O2(aq). If this is true, the second-order rate constant of this process in the system with initial composition of 0.360 M KIO3, 0.345 M H2O2, and 0.055 M HClO4 at 60 °C would be 0.25-0.30 M(-1)·s(-1), depending on the rate of stirring.

Structures of chaos in open reaction systems

By numerically simulating the Bray-Liebhafsky (BL) reaction (the hydrogen peroxide decomposition in the presence of hydrogen and iodate ions) in a continuously fed well stirred tank reactor (CSTR), we find "structured" types of chaos emerging in regular order with respect to flow rate as the control parameter. These chaotic "structures" appear between each two successive periodic states, and have forms and evolution resembling to the neighboring periodic dynamics. More precisely, in the transition from period-doubling route to chaos to the arising periodic mixture of different mixed-mode oscillations, we are able to recognize and qualitatively and quantitatively distinguish the sequence of "period-doubling" chaos and chaos consisted of mixed-mode oscillations (the "mixed-mode structured" chaos), both appearing in regular order between succeeding periodic states. Additionally, between these types of chaos, the chaos without such recognizable "structures" ("unstructured" chaos) is also distinguished. Furthermore, all transitions between two successive periodic states are realized through bifurcation of chaotic states. This scenario is a universal feature throughout the whole mixed-mode region, as well as throughout other mixed-mode regions obtained under different initial conditions.