Spatiotemporal Dynamics Of The Iodate-Sulfite-Thiosulfate Reaction System

The research of spatiotemporal dynamics of the chemical reaction system is mainly on the ordered self-organization structure in time and space of a chemical reaction under the condition of nonlinear and nonequilibrium, such as chemical oscillations, chemical waves and spatiotemporal patterns etc. A systematic research and analysis of the spatiotemporal dynamics of the iodate-sulfite-thiosulfate (IST) reaction system have been done in this paper from the aspects of experiment, mechanism analysis, model and simulation. A rich phenomenon of nonlinear dynamics of the IST system is due to the special mechanism of the mixed-autocatalysis of the hydrogen ion and iodide ion, multi positive and negative processes and feedbacks. The extreme temperature sensitivity of oscillatory behavior can be eliminated by premixing of sulfite and sulfuric acid before entering into the reactor, avoiding local acidification effectively, which provides the guarantee of systematic and comprehensive research on the spatiotemporal dynamics of the IST system. The systematic experimental research on the spatiotemporal dynamics of the IST system focuses on the following four aspects: uniform dynamics in a closed system, temporal self-organization dynamics in a continuously flow stirred tank reactor (CSTR), chemical waves in a closed reaction-diffusion system, and spatiotemporal patterns in a continuously fed unstirred reactor (CFUR). Accordingly, a closed reactor, a CSTR, several petri dishes, and a CFUR are used in the experiments independently.First, the temperature has essential influence on the uniform dynamics of the closed system. The clock reaction occurred and then the damped oscillations did with the temperature increased, at the same time, the induction time decreased. The sharp and high amplitude drop in pH of the clock reaction, single-oscillation, and damped oscillation corresponds to a fast temperature increased which is mainly due to the exothermic and autocatalytic reaction of iodate-sulfite. In addition, the initial concentration of all reagents has the essential influences on the dynamic curves. Second, temperature oscillations, complex oscillations, and temperature compensation have been observed in a CSTR. Temperature oscillations occur with the pH oscillations. During one period of oscillation, the temperature increases rapidly while the pH shows an extremely sharp change,then the temperature decreases when the system is in the high pH state which can be understood by taking into account the periodic interaction between thermal effect of various reactions and heat transfer. The amplitude of the temperature oscillation ranges from 0.1oC to 2.5oC which depends on initial concentrations of the reagents, flow rate, and temperature etc. High -amplitude pH oscillations undergo 11 complex oscillations to another kind of higher-amplitude regular oscillations upon increasing the concentration of sulfite step by step which mainly arises from the two positive feedbacks and the reactions with different dependence on the concentration of H+. Temperature independent period length (temperature compensation) is discovered experimentally in a special temperature interval at different series of initial concentration which may be because the reaction system is not sensitive to the temperature change during the induction time. Third, the coexisted pH pulse and iodine front waves, coexisted pH front and iodine front waves have been observed in special conditions, and propagation mode of the chemical waves can be controlled in gel mediums with different mass fraction in a closed reaction-diffusion system. Fourth, two types of pH pattern and iodine pattern were discovered in the CFUR. The oscillating spots induced route to I3--starch complex labyrinthic patterns is the first discovery in the IST system. The transitions from iodine pulse waves to spots patterns to branching patterns to labyrinthic patterns are attributed to different starch content. Decreasing the concentration of sulfuric acid, stationary lines form between the collided iodine waves. pH front waves and pulse waves were discovered with the pH indicator, and the front instability leading to the pH front oscillations has been studied by adding the sodium polyacrylate into the IST reaction system which reduced the diffusion coefficient of the hydrogen ion effectively. Finally, the simplified four-step Horváth model by addition of an energy conservation equation is used to simulate the uniform dynamics of the closed and open system with the Madonna program. Experimental observations and characteristics, especially in temperature clock reaction, temperature effect on dynamic curves in a batch, temperature oscillations and complex oscillations, are reproduced in the simulation. The innovation research on the project has succeeded in applying the pH nonlinear reaction with multi feedbacks into research of spatiotemporal patterns, which provides ideas for exploring the general conditions and universal rules of the pattern formation, and would have potential applications in designing complex chemical waves and patterns, and pH responsive gels with rhythmical motion, and promotes the understanding of kinds of spatiotemporal structure in biological development and in nature, and is possible to apply the designed dynamic self-organization into practice area such as printing technology, making two-dimentional and three-dimentional structure template, and substrate for biological cell hatch, etc.