Effects of the electrolytes in a closed unstirred Belousov–Zhabotinsky medium
Introduction
The Belousov–Zhabotinsky (BZ) reaction is the most famous oscillatory chemical reaction in a homogeneous liquid phase for studying temporal, spatial and spatiotemporal nonlinear dynamics in nonequilibrium systems [1], [2], [3]. Significant research has been undertaken to understand chemical chaos that have been usually observed in a continuously flow stirred tank reactor (CSTR) [1], [3], [4]. It has been also reported that transient chaotic oscillations are observed in the BZ oscillating chemical reaction in a stirred batch reactor experimentally and numerically [5], [6], [7], [8].
Recently, we have observed aperiodic oscillations during the chemical evolution of a closed unstirred cerium catalyzed BZ system [9]. These aperiodic oscillations are an example of transient chaos because they are sensitive to the initial conditions, the major distinctive features of chaos [9], [10]. The chaotic regime is bounded by two periodic zones. The onset of chaos spontaneously starts by a Ruelle–Takens–Newhouse (RTN) scenario [11], [12] as soon as convection motion couples to diffusion and local kinetics. The chaotic motion continues for about 2 h and ends by an inverse RTN scenario [13]. Differently from the first transition (RTN scenario), the last seems related to the consumptions of the reactants [12], [13]. In previous papers, we studied the effect of different experimental conditions on the system dynamics. We showed that viscosity, temperature and reactor geometry are important control parameters for the transition to chaos [14], [15], [16], [17]. They play an important role in the coupling of chemical kinetics, diffusion and convection allowing or preventing the onset of chaos. A common feature of these systems is that the transition to chaos always takes place through an RTN scenario.
In this paper, we will show that the added electrolyte concentration is another bifurcation parameter responsible for the transition chaos to periodicity of a closed unstirred BZ reaction.
Section snippets
Experimental
All experiments were performed isothermically at ∼20 °C in a batch reactor (spectrophotometer cuvette, 1 × 1 × 4 cm3). The dynamics were monitored by the solution absorbance at 320 nm using quartz UV grade spectrophotometer cuvettes. A double beam spectrophotometer (Varian, series 634) was used. All chemicals were of analytical quality and were used without further purification. The following concentrations of reactants stock solutions were used: Ce(SO4)2 0.004 M, malonic acid 0.30 M, KBrO3 0.09 M; each
Results
In this section, we will illustrate in detail the results obtained adding Na2SO4 to the BZ solution; we obtained analogous results for the others electrolytes. Fig. 1(a) shows the typical spectrophotometric recording in absence of stirring. Two transitions: periodic → aperiodic → periodic can be observed. The Fourier transform of a significant interval of the aperiodic region (Fig. 1(b)), shows a broad band spectrum (Fig. 1(c)); it is a common feature of all aperiodic time series. Our previous
Discussion and concluding remarks
Recently, it has been showed that the BZ reaction in a closed reactor presents a lot of complex behaviors which depend sensibly on the experimental conditions. Many clues led us to claim that the route to chaos following an RTN scenario is due to a coupling between nonlinear chemical kinetics and transport phenomena (diffusion and convection). Unfortunately, we are not able to completely decouple these three phenomena and to tune independently one of them. On the other hand, we can choose
Acknowledgement
This work was supported by MIUR (Italy).
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Cited by (10)
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2011, Chemical Physics LettersChaotic dynamics in an unstirred ferroin catalyzed Belousov-Zhabotinsky reaction
2009, Chemical Physics LettersCitation Excerpt :The origin of the chaotic oscillations was attributed to the coupling among the BZ nonlinear kinetics and the main transport phenomena present in the system: diffusion and natural convection. The unstirred cerium catalyzed system was studied in several experimental conditions [14–17] and particularly by varying the viscosity of the solution with non-ionic micelle-forming surfactants, it was inferred the role of the convection in the onset of the aperiodic behavior. This result was confirmed by using reactors with special geometry [18] and, finally, theoretically proved by numerical simulations [19] where the Grashof number was the bifurcation parameter in the transition from the periodic regime to chaos.
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2009, Ecological ModellingCitation Excerpt :The origin of the chaotic oscillations was attributed to the coupling among the BZ nonlinear kinetics and transport phenomena: diffusion and natural convection. The unstirred cerium catalyzed system was studied in several experimental conditions and it was found that the temperature (Masia et al., 2001), the presence of inert electrolytes (Rossi et al., 2005), the presence of polymers (Marchettini and Rustici, 2000) and the presence of non-ionic micelles (Rustici et al., 2001) act as bifurcation parameters for the dynamics of the system. In particular, by varying the viscosity of the solution with the non-ionic micelle-forming surfactants hexaethylene glycol monodecyl ether and hexaethylene glycol monotetradecyl ether, it was inferred the role of the convection in the onset of the aperiodic behavior.
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