Active Role of a Color Indicator in Buoyancy-Driven Instabilities of Chemical Fronts

Chemical reactions are able to trigger hydrodynamic flows by changing the density of the solutions across reactive interfaces. In this work, an experimental study of the buoyancy-driven hydrodynamic instabilities that can occur when two miscible reactive solutions of an acid−base system are put in contact in the gravity field shows that the patterns observed and the instabilities taking place strongly depend on the presence of a color indicator. A reaction−diffusion−convection model explains how the color indicator can modify the instability scenarios by affecting the density of the solutions and allows one to numerically recover the observed experimental patterns. The present work clearly demonstrates that color indicators should therefore be used with caution in experimental works devoted to analyze reaction−diffusion−convection patterns and instabilities.Fil: Almarcha, C.. Université Libre de Bruxelles; BélgicaFil: Trevelyan, P. M. J.. Université Libre de Bruxelles; BélgicaFil: Riolfo, L. A.. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física. Grupo de Medios Porosos; ArgentinaFil: Zalts, Anita. Universidad Nacional de General Sarmiento. Instituto de Ciencias. Área de Química; ArgentinaFil: El Hasi, Claudio Daniel. Universidad Nacional de General Sarmiento. Instituto de Ciencias; ArgentinaFil: D'onofrio, Alejandro Gustavo. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física. Grupo de Medios Porosos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: De Wit, A.. Université Libre de Bruxelles; Bélgic

Differential diffusion effects on buoyancy-driven instabilities of acid-base fronts: The case of a color indicator

Buoyancy-driven hydrodynamic instabilities of acid-base fronts are studied both experimentally and theoretically in the case where an aqueous solution of a strong acid is put above a denser aqueous solution of a color indicator in the gravity field. The neutralization reaction between the acid and the color indicator as well as their differential diffusion modifies the initially stable density profile in the system and can trigger convective motions both above and below the initial contact line. The type of patterns observed as well as their wavelength and the speed of the reaction front are shown to depend on the value of the initial concentrations of the acid and of the color indicator and on their ratio. A reaction-diffusion model based on charge balances and ion pair mobility explains how the instability scenarios change when the concentration of the reactants are varied.Fil: Kuster, S.. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física. Grupo de Medios Porosos; ArgentinaFil: Riolfo, L. A.. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física. Grupo de Medios Porosos; ArgentinaFil: Zalts, Anita. Universidad Nacional de General Sarmiento; ArgentinaFil: El Hasi, C.. Universidad Nacional de General Sarmiento; ArgentinaFil: Almarcha, C.. Université Libre de Bruxelles; BélgicaFil: Trevelyan, P.M.J.. Université Libre de Bruxelles; BélgicaFil: De Wit, A.. Université Libre de Bruxelles; BélgicaFil: D'onofrio, Alejandro Gustavo. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física. Grupo de Medios Porosos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Chemical control of hydrodynamic instabilities in partially miscible two-layer systems

Hydrodynamic instabilities at the interface between two partially miscible liquids impact numerous applications including sequestration of supercritical liquid CO2 in old petroleum reservoirs or saline aquifers. As an alternative to difficult {\it in situ} studies of the related mixing dynamics, we introduce a new laboratory-scale model system on which buoyancy- and Marangoni-driven convective instabilities of partially miscible two-layer systems can easily be studied and controlled in presence or not of chemical reactions. This system consists in the stratification of a pure ester on top of a denser partially miscible aqueous solution in the gravitational field. The rich convective dynamics observed upon partial dissolution of the ester in the water followed by its hydrolysis highlight the specificity of partially miscible systems as compared to fully miscible or immiscible ones, i.e. the possibility to control the convective pattern and the mixing properties by tuning (i) the intrinsic miscibility of the ester in water, (ii) the feedback of the dissolved species on its own miscibility as well as (iii) the composition and reactivity of the aqueous solution with the ester phase

Asymmetric Rayleigh-Taylor and double-diffusive fingers in reactive systems

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