Hydrodynamic instability arising in horizontally propagating vertical chemical fronts leading to the formation of a single stable convection roll is investigated experimentally in the iodate-arsenous acid reaction for various stoichiometry. In the presence of a free surface, the tilted reaction front becomes more elongated due to the evaporation of the surface active iodine and the decrease in the surface tension during the reaction. The experimental conditions are then identified where Marangoni instability represents the driving force for the distortion of the reaction front at the surface.

Horizontally propagating chemical fronts leading to the formation of a single stable convection roll are investigated in the iodate-arsenous acid reaction with arsenous acid stoichiometrically limiting, leaving the surface active iodine present in the product mixture. In sufficiently thin solution layers with open upper surface, the contribution of Marangoni instability is significantly enhanced. Acting in the same direction as buoyancy driven instability, it distorts the entire tilted reaction front that becomes 50% more elongated. The corresponding three-dimensional calculations based on the empirical rate-law of the reaction corroborate the experimental findings.

a b s t r a c tHorizontally propagating chemical fronts have been studied in the acid-catalyzed chlorite-tetrathionate reaction. Unusual cellular fingers develop in a relatively thin solution layer. Double-diffusive convection is among the driving forces in the pattern formation arising from the addition of a polyelectrolyte which immobilizes and reversibly removes the autocatalyst hydrogen ion in a controlled manner and drastically slows down the front. Convection therefore becomes significant in the thin horizontal solution layer. To corroborate our results we have measured the solution densities and viscosities, and determined the diffusion coefficients by PFGSE 1 H-NMR.

Planar reaction fronts resulting from the coupling of exothermic autocatalytic reactions and transport processes can be deformed by convection in the presence of gravity field. We have experimentally investigated how buoyancy affects the spatiotemporal pattern formation at various solution thicknesses in three-dimensional medium. In the chlorite-tetrathionate reaction, a stable structure propagating horizontally with constant velocity and geometry develops when appropriately thick solutions are studied. Both the horizontal and the vertical projections of the resulting three-dimensional structures are quantitatively characterized: the smooth leading edge of the front is independent of the solution thickness and the structured trailing edge ends in a center cusp with a constant angle.

Horizontally propagating fronts in the iodate-arsenous acid reaction are investigated experimentally in a vertically oriented Hele-Shaw cell by varying the height of liquid layer for various stoichiometry. At the preset conditions, a stable pattern develops which can be characterized by its mixing length defined as the standard deviation of the front position in the direction of propagation. The mixing length scales with the height of the reaction vessel, and although the exponent significantly changes by varying the ratio of the reactants, it has a universal value when the reaction front is thin and simple convection arises.