Flow waves of hierarchical pattern formation induced by chemical waves: The birth, growth and death of hydrodynamic structures

We introduce a short review of chemically driven convection together with a series of our experiments on hydrodynamic instabilities induced by chemical waves excited in the batch reactor of a Belousov–Zhabotinsky reaction. Several unresolved phenomena are picked out and possible mechanisms are discussed extensively. Interesting features of these phenomena can be summarized as being caused by the ‘global and dynamic hydrodynamic pattern induced by chemical waves’. These chemically induced global pattern of hydrodynamic phenomena may not be simply explained by the reaction–diffusion–convection model based on Marangoni instability (surface tension-driven convection), which produces only a localized structure of the convection pattern. Observed flow waves show global and dynamic patterns of convection that generate a functional structure associated with hierarchical patterns appearing in the reaction–diffusion–convection system. In particular, we clarify the existence of a continuous stream of hydrodynamic flow with growing amplitude and its rotating direction. We find that the flow does not stabilize to a motionless state until the system has self-collapsed. This new picture of the flow waves requires a revision of the reaction–diffusion–convection model. The established flow structure can be regarded as a mixing and/or transport process to supply the substrate from the peripheral region to the centre of the chemical waves to sustain the reaction. This characteristic may be a function of the hierarchical structure. A new mechanism for the viscous–elastic feature of the gas–liquid interface is discussed in order to understand these curious phenomena of interest.