We report new chemoconvective pattern formation phenomena observed in a two-layer system of miscible fluids filling a vertical Hele-Shaw cell. We show both experimentally and theoretically that the concentration-dependent diffusion coupled with the frontal acid-base neutralization can give rise to formation of the local unstable zone low in density resulting in a perfectly regular cell-type convective pattern. The described effect gives an example of yet another powerful mechanism which allows the reaction-diffusion processes to govern the flow of reacting fluids under gravity condition.

In this paper, the development of frontal polymerization under conditions of free convective motion of a reactive mixture is studied experimentally and numerically. The convection is caused by the reaction exothermicity and by the density change, because the polymer is more dense than the monomer. The propagation of polymerization fronts with convection is studied for the photoinitiated polymerization of an aqueous solution of acrylamide. Comparison of terrestrial and space experiments with the results of numerical simulation shows that convection can lead to the formation of inhomogeneities in the polymer product; it can change the speed of propagation of the reaction front and even change the reaction from frontal to volumetric.