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1. |
Front cover |
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Physical Chemistry Chemical Physics,
Volume 8,
Issue 9,
2006,
Page 1025-1025
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ISSN:1463-9076
DOI:10.1039/b601915n
出版商:RSC
年代:2006
数据来源: RSC
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Inside front cover |
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Physical Chemistry Chemical Physics,
Volume 8,
Issue 9,
2006,
Page 1026-1026
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ISSN:1463-9076
DOI:10.1039/b601921h
出版商:RSC
年代:2006
数据来源: RSC
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3. |
Contents |
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Physical Chemistry Chemical Physics,
Volume 8,
Issue 9,
2006,
Page 1027-1032
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ISSN:1463-9076
DOI:10.1039/b601922f
出版商:RSC
年代:2006
数据来源: RSC
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Spatial bistability, oscillations and excitability in the Landolt reactionElectronic supplementary information (ESI) available: Video of aperiodic oscillations in the Landolt reaction operated in an annular OSFR. See DOI:10.1039/b515620c |
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Physical Chemistry Chemical Physics,
Volume 8,
Issue 9,
2006,
Page 1105-1110
István Szalai,
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摘要:
1IntroductionThere has been great interest in studying waves and patterns in reaction–diffusion systems across a wide range of scientific disciplines in recent years. Nonlinear chemical systems are paradigms for non equilibrium self-organization phenomena and are often thought to provide simplified versions of spatio-temporal patterning phenomena observed in biological systems.1–5Reactions leading to such phenomena include competing chemical activation and inhibition kinetic pathways. During the last decades more than 300 oscillating reactions were discovered, covering a broad range of different chemical element compounds.1,3,6Oscillations and traveling wave patterns are associated with time-scale separation. These are typically fast activation and slow inhibition systems. Remarkably, in contrast to the large number of known oscillatory reactions, only a very few have been shown to produce sustained traveling waves and patterns. To determine the actual conditions under which reaction–diffusion patterns can be made, and discover possible new pattern bifurcations in bench experiments, it is essential to explore chemically different systems.Recently, oscillations and the excitability were found in the chlorite–tetrathionate system, operated in an open gel reactor. This reaction is autocatalytic for protons, but in the mechanism there is no slow inhibition pathway. Consequently, in an continuous stirred tank reactor (CSTR) the reaction shows only bistability between steady states. In a one-side-fed spatial reactor (OSFR), consisting of a piece of gel in contact with the contents of a CSTR,7the reactants and products are continuously exchanged between the gel part and the CSTR. The gel medium avoids convective transport and thus enables chemical patterns resulting solely from the interplay between reaction and diffusion to develop. It was shown that the much faster diffusivity of the proton, the activator, compared to that of input reagents (“long range activation”) can account for the observed oscillatory phenomena in the OSFR.8,9This is a diffusion driven instability, a new class of the instabilities that generate spatio-temporal oscillations. It was anticipated9,10that such a type of oscillatory instability could be observed in many if not all pH autocatalytic reactions. The present report provides a possible second such example and is a part of our systematic experimental studies on spatio-temporal dynamics of bistable reaction–diffusion systems.8–13In all open gel reactors the time scale of diffusive exchanges of chemicals between the core of the gel and the solutions at the boundary depend on the width (the length scale over which the diffusive feed has to operate) of the gel. This geometric parameter plays a crucial role in the existence and stability of spatial states.8,9,11–14It has been shown, both experimentally8,11and theoretically15that “spatial bistability” is a common phenomenon when a self-activated reaction is operated in an OSFR. This spatial bistability phenomenon corresponds to overlapping domains of stability of two different spatial steady states in the gel for the same uniform state of the CSTR. These states preserve the symmetry imposed by the feed at the boundary. The first experimental demonstration was made with the chlorine dioxide–iodide (CDI) reaction.11Later, spatial bistability was also found in the pH-driven autocatalytic chlorite–tetrathionate (CT) reaction.8Let us briefly recall the basis of spatial bistability. Consider an autocatalytic reaction in a CSTR. The chemical state of this reactor depends on the time scale over which the reaction evolves and on the input flow rate. If the input flow rate is large, the extent of the reaction is small and the composition of the CSTR is close to the composition of the input flow (“flow state”, F). If the input flow rate is small, the extent of the reaction is large, the composition in the CSTR is close to that, one would obtain, in a closed reactor with the same initial concentrations. This state is referred to as the “thermodynamic state”, T. The stability domain of these two states can overlap over a range of control parameter, this is standard uniform state bistability.Now, consider a gel in contact with the contents of a CSTR that belongs to the F state. The gel is diffusively fed by fresh reactants from one side. The composition in the depth of the gel depends on the diffusion time and on the time scale of the reaction. For continuity reason, next to the gel–CSTR boundary the composition in the gel is similar to that of the CSTR. Far from this boundary, when the diffusion time is larger than the typical time scale of the reaction, the extent of reaction becomes large and the composition is then similar to that of the T state. Within an intermediate range of the size two spatial states can coexist for the same chemical concentration at the boundary. In one state the composition belongs everywhere to the F state branch; by extension, we also call this state of the gel content F. In the other spatial state the inner part of the gel has a composition close to that of the T state while a boundary layer at the gel/CSTR interface remain in the F state. Thus, this second spatial state is characterized by a relatively sharp chemical front that naturally follows the boundary symmetry. We say that this other spatial state is a mixed state M.Here, we study the spatio-temporal dynamics of the Landolt iodate–sulfite (IS) reaction16operated in an annular OSFR. The IS reaction is autocatalytic both for protons and iodide ions. Rabai and coworkers17pointed out that the dominant positive feedback process is the autocatalytic oxidation of hydrogen sulfite:1IO3−+ 3HSO3−→ I−+ 3SO42−+ 3H+Meanwhile the iodide autocatalytic process only becomes important at the end of the oxidation of sulfite when the pH drops below 5:2IO3−+ 5I−+ 6H+→ 3I2+ 3H2O3I2+ HSO3−+ H2O → 2I−+ SO42−+ 3H+Reaction (2)plays also an important role as a proton consuming process. Note that, the IS reaction is a subsystem of the iodate–sulfite–ferrocyanide pH-oscillator,18which can produce a large variety of spatial patterns in an OSFR14,19and the mechanism of which is not fully understood, yet.
ISSN:1463-9076
DOI:10.1039/b515620c
出版商:RSC
年代:2005
数据来源: RSC
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5. |
Back matter |
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Physical Chemistry Chemical Physics,
Volume 8,
Issue 9,
2006,
Page 1122-1122
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ISSN:1463-9076
DOI:10.1039/b601936f
出版商:RSC
年代:2006
数据来源: RSC
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6. |
Back cover |
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Physical Chemistry Chemical Physics,
Volume 8,
Issue 9,
2006,
Page 1123-1124
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ISSN:1463-9076
DOI:10.1039/b601923b
出版商:RSC
年代:2006
数据来源: RSC
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