Chemohydrodynamic patterns
due to the interplay of buoyancy-driven
instabilities and reaction–diffusion patterns are studied experimentally
in a vertical quasi-two-dimensional reactor in which two solutions
A and B containing separate reactants of the oscillating Belousov–Zhabotinsky
system are placed in contact along a horizontal contact line where
excitable or oscillating dynamics can develop. Different types of
buoyancy-driven instabilities are selectively induced in the reactive
zone depending on the initial density jump between the two layers,
controlled here by the bromate salt concentration. Starting from a
less dense solution above a denser one, two possible differential
diffusion instabilities are triggered depending on whether the fast
diffusing sulfuric acid is in the upper or lower solution. Specifically,
when the solution containing malonic acid and sulfuric acid is stratified
above the one containing the slow-diffusing bromate salt, a diffusive
layer convection (DLC) instability is observed with localized convective
rolls around the interface. In that case, the reaction–diffusion
wave patterns remain localized above the initial contact line, scarcely
affected by the flow. If, on the contrary, sulfuric acid diffuses
upward because it is initially dissolved in the lower layer, then
a double-diffusion (DD) convective mode develops. This triggers fingers
across the interface that mix the reactants such that oscillatory
dynamics and rippled waves develop throughout the whole reactor. If
the denser solution is put on top of the other one, then a fast developing
Rayleigh–Taylor (RT) instability induces fast mixing of all
reactants such that classical reaction–diffusion waves develop
later on in the convectively mixed solutions.