Sodium polyacrylate-induced pH pattern formation and starch-induced iodine pattern formation were investigated in the iodate-sulfite-thiosulfate (IST) reaction in a one-side fed disc gel reactor (OSFR). As binding agents of the autocatalyst of hydrogen ions or iodide ions, different content of sodium polyacrylate or starch has induced various types of pattern formation. We observed pH pulses, striped patterns, mixed spots and stripes, and hexagonal spots upon increasing the content of sodium polyacrylate and observed iodine pulses, branched patterns, and labyrinthine patterns upon increasing the starch content in the system. Coexistence of a pH front and an iodine front was also studied in a batch IST reaction-diffusion system. Both pH and iodine front instabilities were observed in the presence of sodium polyacrylate, i.e., cellular fronts and transient Turing structures resulting from the decrease in diffusion coefficients of activators. The mechanism of multiple feedback may explain the different patterns in the IST reaction-diffusion system.

Temperature oscillations and complex pH oscillations in the IO(3)(-)-SO(3)(2-)-S(2)O(3)(2-) system were observed in a continuously flow stirred tank reactor. During one period of oscillation, the temperature increases rapidly while the pH shows an extremely sharp change. High-amplitude pH oscillations undergo 1(1) complex oscillations (L(S), oscillations with L large peaks and S small peaks per period) to another kind of higher-amplitude regular oscillations upon increasing the concentration of sulfite step by step. Importantly, the longstanding experimental phenomena, the extraordinary temperature sensitivity of oscillatory behavior reported 20 years ago by Rabai and Beck, can be eliminated by premixing of sulfite and sulfuric acid before entering into the reactor, avoiding local acidification, which brings out fluctuation and temperature sensitivity. The temperature oscillations can be understood by taking into account the interaction between thermal effect of various reactions and heat transfer. Experimental observations, both temperature oscillations and 1(1)-type pH oscillations, are reproduced with a four-step Horvath model by addition of an energy-balance equation. This new detailed dynamical behavior would have potential applications in designing complex chemical waves and pH responsive gels with rhythmical motion.

There is increasing interest in using chemical clock reactions to drive material formation; however, these reactions are often subject to chemoconvective effects, and control of such systems remains challenging. Here, we show how the transfer of oxygen at the air−water interface plays a crucial role in the spatiotemporal behavior of the iodine clock reaction with sulfite. A kinetic model was developed to demonstrate how the reaction of oxygen with sulfite can control a switch from a low-iodine to high-iodine state under well-stirred conditions and drive the formation of transient iodine gradients in unstirred solutions. In experiments in thin layers with optimal depths, the reaction couples with convective instability at the air−water interface forming an extended network-like structure of iodine at the surface that develops into a spotted pattern at the base of the layer. Thus, oxygen drives the spatial separation of iodine states essential for patterns in this system and may influence pattern selection in other clock reaction systems with sulfite.

In a continuous flow stirred tank reactor (CSTR), the reaction of thiourea-iodate-sulfite (TuIS) exhibits a rich variety of complex oscillations in pH. The transitions from 1(n) type oscillations to 1(3), 1(2) type and simple oscillations were observed on decreasing the flow rate gradually in small steps at 30.2 °C and 20.5 °C, respectively. The transitions from 1(n) type oscillations to 1(0)1(4), 1(0)1(3) type and simple oscillations were observed as well on increasing the temperature in small steps at a given flow rate. Based on the analogous iodate-sulfite-thiosulfate system a simple empirical rate law model is suggested to give a sound agreement between the experimental and simulated results on the complex oscillatory behaviour. A possible explanation of the emergence of the simple empirical rate law model from the mechanism of the individual reactions of the TuIS system is also discussed.