1,721,007 research outputs found
Scroll waves in the Belousov-Zhabotinsky reaction: exploitation of O2- effect on the ferroin-catalysed system
No full textEffect of oxygen on wave propagation in the ferroin-catalysed Belousov-Zhabotinsky reaction
No full textAn organic-based pH oscillator
No full textIn a recent paper, we suggested that the acid- or base-catalyzed dehydration of a hydrated carbonyl compound provides a suitable foundation for an organic-based pH oscillator. Here we present the first experimental example of such an oscillator in a flow reactor, utilizing the base-catalyzed dehydration of methylene glycol as a source of positive feedback (OH- autocatalysis) coupled with the base-catalyzed hydrolysis of gluconolactone for negative feedback (H+ production). The large amplitude oscillations (between pH 7 and 10) are reproduced in a kinetic model of the reaction. Such experiments present new possibilities in the design of pH oscillators
Complex behavior in the formaldehyde-sulfite reaction
No full textThe formaldehyde−sulfite reaction is an example of an “acid-to-alkali” clock. It displays an induction period, during which the pH varies only slowly in time, followed by a reaction event, during which the pH increases rapidly by several units. When the reaction is performed in a closed (batch) reactor, the clock time is found to increase with a decrease in initial concentrations of formaldehyde and sulfite and an increase in the total initial concentration of S(IV). At long times, following the clock event, there is a slow decrease in pH. In an open (flow) reactor, bistability between a low-pH steady state (pH ∼ 6−8) and a high-pH steady state (pH ∼ 11) is observed. Additionally, we report the existence of sustained, small-amplitude oscillations in pH in this system. An extended kinetic mechanism reproduces the batch behavior but fails to account for the complex behavior observed in the flow reactor. Possible additional reaction steps are discussed
Analysis of reaction-diffusion waves in the ferroin-catalysed Belousov- Zhabotinsky reaction
No full textA novel route to pH oscillators
No full textThe formaldehyde–sulfite reaction is an acid to alkali clock reaction in batch, which displays complex behaviour in a flow reactor. Current published mechanisms do not account for the behaviour in an open system. In this Letter, we construct a minimal model based on this system and demonstrate that a base-catalysed rate-determining step coupled with an appropriate OH− consuming reaction can result in bistability and oscillations. The model may provide a method for the design of organic-based pH oscillators
Propagation of chemical waves across inexcitable gaps
No full textThe propagation of chemical reaction–diffusion waves across a sequence of gaps is studied experimentally using catalyst-printed membranes. We find that a wave fails to propagate across the entire reaction domain if the width W of a gap is greater than a critical value Wcr or if the spacing S between two successive gaps is less than a critical value Scr. For values of W ≪ Wcr and S ≫ Scr then successful propagation across the entire domain is highly probable, irrespective of the number of gaps. For values of W and S close to the critical values, the probability of failure increases with increasing number of gaps
Acid autocatalysis and front propagation in water-in-oil microemulsions
No full textExperimental results are presented of an acid autocatalytic reaction (the bromate-sulfite clock reaction) performed in water-in-oil (w/o) microemulsions with neutral (Triton X-100, TX) or cationic (CTAB) surfactants. The characteristics of the pH-sensitive reaction in the stirred system are found to depend on the molar ratio of water to surfactant (ω0) and the nature of the surfactant. The well-stirred reaction (clock) time is faster in the TX w/o microemulsion and slower in the CTAB w/o microemulsion compared to the aqueous phase clock. The pH change is reduced in the TX system and the initial and final pH are shifted to higher values in the CTAB system. The unstirred water-in-oil microemulsions support propagating acid reaction fronts with speeds up to a factor of 10 lower than the aqueous phase fronts. The results are explained through consideration of the effect of the confinement of water in the nanosized droplets on rates and equilibria and assuming front propagation is driven by the diffusion of hydrated reverse micelles
Reaction-diffusion waves; homogeneous and inhomogeneous effects
No full textExperimental evidence for the spontaneous formation of spiral waves and crossing wave patterns for the Belousov–Zhabotinsky reaction in solution are presented. Also observed are so-called ‘lateral instabilities’ with the spontaneous deformation of circular fronts in systems of low excitability. Lateral instabilities in resin-based systems, with the redox catalyst immobilised on ion-exchange beads, and the effect of the ageing of solutions, are also reported
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