Study of the transition to higher iodide in the malonic acid Briggs–Rauscher oscillator

Non-autonomous zinc-methylimidazole oscillator and the formation of layered precipitation structures in a hydrogel

Oscillations are one of the intrinsic features of many animate and inanimate systems. The oscillations manifest in the temporal periodic change of one or several physical quantities describing the systems. In chemistry and biology, this physical quantity is the concentration of the chemical species. In most chemical oscillatory systems operating in batch or open reactors, the oscillations persist because of the sophisticated chemical reaction networks incorporating autocatalysis and negative feedback. However, similar oscillations can be generated by periodically changing the environment providing non-autonomous oscillatory systems. Here we present a new strategy for designing a non-autonomous chemical oscillatory system for the zinc-methylimidazole. The oscillations manifested in the periodic change of the turbidity utilizing the precipitation reaction between the zinc ions and 2-methylimidazole (2-met) followed by a partial dissolution of the formed precipitate due to a synergetic effect governed by the ratio of the 2-met in the system. Extending our idea spatiotemporally, we also show that these precipitation and dissolution phenomena can be utilized to create layered precipitation structures in a solid agarose hydrogel.

Multiple iodide autocatalysis paths of chemo-hydrodynamical patterns in the Briggs-Rauscher reaction

Autocatalytic feedback is often regarded as the core step for the chemo-hydrodynamical patterns in the nonlinear reaction system. The Briggs-Rauscher (BR) reaction shows sequential chemo-hydrodynamical patterns with three states, i.e. labyrinth, high iodine state, and rotating dendritic patterns. The short-lived labyrinth patterns, depending on [Mn²⁺]₀, the ratio of [CH₂(COOH)₂]₀ and [KIO₃]₀ and light intensities, result from iodide autocatalytic loop, which has three paths (involving Mn²⁺-induced radical reactions, the oxidation of iodomalonic compounds, and light-induced radical reactions, respectively). The high iodine state appears in a high ratio of [CH₂(COOH)₂]₀ and [KIO₃]₀, relating to the autocatalytic path involving the oxidation of iodomalonic compounds. The light-induced radical autocatalytic path can act as a convenient control parameter to modulate the patterns in the first stage by increasing the iodine radicals. The dendritic patterns in the third stage result from the Marangoni effect caused by the evaporation of the solutions and reactions between H₂O₂ and iodine-containing species, which is independent of [CH₂(COOH)₂]₀ and [Mn²⁺]₀. This work contributes to a better understanding of the complex spatiotemporal patterns in the chemo-hydrodynamical system.

Spontaneous Symmetry Breaking: The Case of Crazy Clock and Beyond

In this work, we describe the crazy-clock phenomenon involving the state I (low iodide and iodine concentration) to state II (high iodide and iodine concentration with new iodine phase) transition after a Briggs–Rauscher (BR) oscillatory process. While the BR crazy-clock phenomenon is known, this is the first time that crazy-clock behavior is linked and explained with the symmetry-breaking phenomenon, highlighting the entire process in a novel way. The presented phenomenon has been thoroughly investigated by running more than 60 experiments, and evaluated by using statistical cluster K-means analysis. The mixing rate, as well as the magnetic bar shape and dimensions, have a strong influence on the transition appearance. Although the transition for both mixing and no-mixing conditions are taking place completely randomly, by using statistical cluster analysis we obtain different numbers of clusters (showing the time-domains where the transition is more likely to occur). In the case of stirring, clusters are more compact and separated, revealed new hidden details regarding the chemical dynamics of nonlinear processes. The significance of the presented results is beyond oscillatory reaction kinetics since the described example belongs to the small class of chemical systems that shows intrinsic randomness in their response and it might be considered as a real example of a classical liquid random number generator.

Design of non-autonomous pH oscillators and the existence of chemical beat phenomenon in a neutralization reaction

The beat in physical systems is a transparent and well-understood phenomenon. It may occur in forced oscillatory systems and as a result of the interference of two waves of slightly different frequencies. However, in chemical systems, the realization of the latter type of the beat phenomenon has been lacking. Here we show that a periodic titration of acid and alkaline solutions with each other using programmable syringe pumps in a continuous stirred-tank reactor exhibits the beat phenomenon in the temporal pH oscillation pattern if the time periods of sinusoidal inflow rates of the reagents are slightly different. Interestingly, the frequency of the chemical beat pattern follows the well-known relationship from physics, namely the frequency of the beat is equal to the absolute value of the difference of the two wave frequencies. Based on our strategy, we can design and engineer non-autonomous pH oscillatory systems, in which the characteristics of the temporal oscillations (amplitude, time period) can easily and precisely be controlled by the experimental conditions such as the inflow rates and feed concentrations. The demonstrated phenomena can be exploited in practical applications, we use the non-autonomous pH oscillators to drive the reversible assembly and disassembly of pH-sensitive building blocks (oleic acid and gold nanoparticles), both highly relevant in nanotechnology and biomedical applications.

Chloride Ion Inhibition, Stirring, and Temperature Effects in an Ethylacetoacetate Briggs-Rauscher Oscillator in Phosphoric and Hydrochloric Acids in a Batch Reactor

Briggs-Rauscher oscillating reaction has been investigated in hydrochloric acid media and in the presence of added chloride ions in phosphoric acid media in a batch reactor using ethylacetoacetate as the organic substrate. The changes in key oscillation parameters, namely, induction period, oscillation period, amplitude, and so forth, have been explained in terms of the steps of the skeleton mechanism proposed by Furrow and Noyes and by de Kepper and Epstein. In spite of several shortcomings as outlined in section 2 in the text, the same mechanistic steps are good enough to explain qualitatively most of the changes in oscillation parameters under different stirring rates and temperatures in phosphoric acid and hydrochloric acid media, particularly stirring effects explained well by the theory of imperfect mixing. Potential data indicate that 0.018 M HCl medium has the ability to exhibit near-zero/zero amplitudes before cessation of oscillations. Inhibition reactions from a low Cl^- concentration in the 0.018 M HCl media appear to be responsible for this interesting dynamical transformation, as toward the end of oscillations, the difference between [I^-] and [I^-]_crit [see eq J in the text] becomes very small because of depleted component chemicals due to chemical reactions.

Transition from Low to High Iodide and Iodine Concentration States in the Briggs-Rauscher Reaction: Evidence on Crazy Clock Behavior

The Briggs-Rauscher reaction containing malonic acid may undergo a sudden transition from low (state I) to high iodide and iodine (state II) concentration states after a well-defined and strongly reproducible oscillatory period. This study clearly shows that even though the time-dependent behavior of the oscillatory state is reproducible, the time lag necessary for the appearance of the state I to state II transition after the system leaves the oscillatory state becomes irreproducible for an individual kinetic run. This crazy clock behavior of the state I to state II transition is identified by repeated experiments in which stirring rate is taken as a control parameter and all other parameters such as initial conditions, temperature, vessel surface, and the age of solution were kept constant. Surprisingly, a better stirring condition does not make the transition reproducible; it simply does not allow the transition to happen at all. The proposed mechanism, additional explanations, and proposals for this irreproducibility of state I to state II transition have been presented. Considering the fact that the number of crazy clock reactions is only a few, this study may contribute to a better understanding of fundaments of this phenomenon.