Convective and periodic motion driven by a chemical wave

Abstract

The generation of convective flow by a chemical wave was studied experimentally on a mm-sized droplet of Belousov-Zhabotinsky ͑BZ͒ reaction medium. A propagating chemical wave causes a transient increase in interfacial tension, and this local change in interfacial tension induces convection. The observed flow profile was reproduced with a numerical simulation by introducing the transient increase in interfacial tension to a modified Navier-Stokes equation coupled with a chemical kinetic equation; a modified Oregonator. We also observed the periodic motion of a BZ droplet floating on an oil phase. Such periodic motion is attributed to the rhythmic change in interfacial tension. The observed periodic convective motion coupled with a chemical reaction is discussed in relation to chemo-mechanical energy transduction under isothermal conditions.

Mathematical model for self-propelled droplets driven by interfacial tension

“…Spontaneous motion driven by inhomogeneity in interfacial tension is an area of study relating to active matter. [5][6][7][8][9][10][11][12][13][14][15][16] For example, alcohol droplets placed on water move spontaneously while exhibiting deformations to their shape. 17,18 Since such systems are relatively simple, it is possible to perform experiments under a broad parameter space; therefore, such a setting provides a preferable experimental framework for investigations of general aspects.…”

Spontaneous Motion of a Belousov–Zhabotinsky Reaction Droplet Coupled with a Spiral Wave

“…7,8 The detailed mechanism of the BZ reaction has been investigated using a simple mathematical model, the Oregonator. 9 This BZ droplet motion, which we reported previously, 5,6 was due to the change in the interfacial tension of a ferroincatalyzed BZ medium; i.e., a BZ medium in the oxidized state has a higher interfacial tension than that in the reduced state. 10,11 Thus, around the droplet, convective flow was induced through the Marangoni effect, 12,13 which drives the droplet.…”

“…3,4 Recently, we reported on the motion of a millimeter-sized droplet of a BelousovZhabotinsky (BZ) reaction medium coupled with pattern formation inside it. 5,6 The BZ reaction is an oscillatory chemical reaction that is easily achieved by mixing several chemical reagents. It also exhibits spontaneous pattern formation, such as a target pattern or a spiral pattern, when it is settled without stirring.…”

Quasi-elastic Laser Scattering for Measuring Inhomogeneous Interfacial Tension in Non-equilibrium Phenomena with Convective Flows

“…It was reported previously that the concentration gradient of a metal catalyst complex induced a solutal Marangoni effect, resulting in convective flow or motion. [21][22][23][24][25]61 To clarify the changes in the surface tension and the contribution of the Marangoni effect to the BZ reaction, surface-tension measurements were attempted for BZ reactions with or without stirring. [62][63][64] However, surface-tension measurements are impossible in unstirred air-liquid and liquid-liquid systems because the conventional probe used for the measurement obstructs the propagation of the chemical wave in the BZ reaction.…”

“…[9][10][11][12][13][14][15][16][17][18] The BelousovZhabotinsky (BZ) reaction, which generates chemical oscillations in a bulk material, also produces sophisticated spatio-temporal patterns in an unstirred system. [19][20][21][22][23][24][25] Interfacial tension and its spatial distribution are key properties in these non-equilibrium and non-linear phenomena, since they govern molecular transport. An inhomogeneous interfacial tension distribution gives rise to a convective flow by the Marangoni effect, which is induced by a thermal gradient or a chemical content gradient.…”