Controlling Chemical Chaos in the Belousov-Zhabotinsky Oscillator.

Chaos is ubiquitous in Nature and represents one of the most fascinating expressions of real world complexity. Depending on the specific context, the onset of chaotic behaviours can be undesirable, thus, controlling the mechanisms at the basis of chaotic dynamics represents a cutting-edge challenge in many areas, including cardiology, information processing, hydrodynamics and optics, to name a few. In this work we review our recent results showing how, in chemical reactions, the active interplay between a nonlinear kinetics and hydrodynamic instabilities can be exploited as a general mechanism to induce and control chemical chaos. To this end, we consider as a model system the Belousov-Zhabotinsky (BZ) reaction. Thanks to a chemo-hydrodynamic coupling, the reaction can undergo chaotic oscillations when carried out in batch conditions. Chaos appears and disappears by following Ruelle-Takens-Newhouse scenario both in the cerium-and ferroin-catalyzed BZ systems. Here, we present experimental evidence that the transition to chemical chaos can be directly controlled by tuning either kinetic or hydrodynamic parameters of the system. Experiments were simulated by using a reaction-diffusion-convection (RDC) model where the nonlinear reaction kinetics are coupled to the Navier-Stokes equations. Numerical solutions of the RDC model clearly indicate that natural convection can feedback on the spatio-temporal evolution of the concentration fields and, in turn, changes bulk oscillation patterns. Distinct bifurcations in the oscillation patterns are found when the Grashof numbers (governing the entity of convective flows into the system) and the diffusion coefficients of the chemical species are varied. The consumption of the initial reagents is also found to be a critical phenomenon able to modulate the strength of the RDC coupling and drive order-disorder transitions.