Probing The Ferroin-catalysed Belousov-zhabotinksy Reaction In Flow

Trigger waves were produced in the ferroin-catalysed BZ reaction using an Ag-Pt electrode system and then placed into Taylor couette flow. The chemistry and flow of the system was manipulated providing a vast array of controllable wave propagation mechanisms and velocities. Nature exhibits the ability to produce complex patterns with relative ease and flamboyance.1,2 Chemical analogues to these natural pattern forming systems help us to decipher the underlying mechanisms in the hope that we can emulate the efficiency and precision found in nature, allowing advances in fields such as medicine and chemical engineering.3,4 The Belousov-Zhabotinsky (BZ) reaction is known for its distinct oscillatory behaviour, and in flow regimes produces chemical reaction-diffusion advection waves (RDA).5,6,7 Here we report an innovative new method for producing single blue trigger RDA waves in the red solution under Taylor couette flow, and also fully categorise the behaviour of the ferroin catalysed BZ reaction in flow, which has never been achieved prior to this. The ferroin catalysed BZ reaction contains 3 main groups to its mechanism8: a) Bromide removal steps b) Ferroin oxidation c) Ferroin reduction and production of bromide In order to generate trigger waves within the solution, the initial bromide concentration must be high enough that general a) type processes cannot remove enough bromide for b) to begin, but low enough that an external perturbation can begin b) type reactions. A range of literature sources were found to use a positively biased silver electrode with respect to a platinum electrode to remove the bromide in solution by forming AgBr. After testing a range of systems unsuccessfully, a successful system was found to easily produce waves and remain stable for long periods of time without perturbation. 9,10,11,12 Once a stable solution had been established, a method for triggering a wave within flow was developed using a voltage oscillator, couette cell and stepper motor. By pulsing the voltage oscillator for 10 seconds at +1.3V, the silver electrode at the base of the couette cell produced a blue chemical wave which began to propagate through the couette cell. The inner rod in the couette cell was then rotated to generate Taylor vortex flow, in which the chemical wave then coupled with flow to produce RDA waves. Maintaining a voltage of -1.2V immediately after a positive pulse also prevents further wave production after the initial wave has formed. Taylor vortex flow produces pairs of counter rotating vortices in which advection dominates wave propagation at the outside of the vortices, whilst diffusion dominates wave propagation into the centre of vortices and across the separatrix (the gap between vortex pairs).