Pentanary Cross‐Diffusion in Water‐in‐Oil Microemulsions Loaded with Two Components of the Belousov–Zhabotinsky Reaction

Abstract

We measure cross-diffusion coefficients in a five-component system, an aerosol OT (AOT) water-in-oil microemulsion loaded with two constituents of the Belousov-Zhabotinsky (BZ) reaction (H(2) O/AOT/BZ1/BZ2/octane). The species BZ1 is either NaBr, an inhibitor of the BZ reaction, or ferroin, a catalyst for the reaction. As species BZ2, we choose Br(2) , an intermediate in the reaction. The cross-diffusion coefficients between BZ1 and BZ2 are found to be negative, which can be understood in terms of complexation between these species. Using a four-variable model for the BZ reaction, we find that the cross-diffusion coefficients measured here can lead to a noticeable shift in the onset of Turing instability in the BZ-AOT system.

Cross-diffusion-induced convective patterns in microemulsion systems

“…Good qualitative agreement between the instability scenarios predicted by the theoretical model and the experimentally observed convective pattern is obtained. As the microemulsion system under study here is known to exhibit a large variety of patterns where crossdiffusion may couple to reaction processes, 7 our results provide characterisation of a good candidate for future studies of crossdiffusion-driven RDC instabilities. In the following sections, we introduce the cross-diffusive properties of AOT microemulsions and describe the experimental methods.…”

“…In the following sections, we will refer to the concentration . 7 In particular, Table 1 reports the diffusion matrix D of a quaternary system where NaBrO 3 is the third component. Verification experiments were also run by using the colored salts KMnO 4 or K 2 Cr 2 O 7 in the place of NaBrO 3 .…”

“…Although cross-diffusion coefficients depend on the chemical composition of the system, as a first approximation, we consider them as constant here. 7 In a 1D spatial domain of length L z along the vertical z-axis, sketched in Fig. 5, we consider a homogeneous initial distribution A(z,0) = A 0 , B(z,0) = B 0 , while a sharp initial gradient is imposed for the solute C(z,t), according to the step function By introducing the solutions to the diffusion problem defined by eqn (4)- (6), in eqn (7), we can compute the spatio-temporal evolution of the dimensionless density profile.…”

“…In particular, the influence of cross-diffusion on RD Turing patterns and wave instabilities has been studied both theoretically [1][2][3][4][5][6] and experimentally. 7 Typical systems in which cross-diffusion-driven reactive patterns can be studied include AOT (sodium bis(2-ethylhexyl)sulfosuccinate aerosol OT) micelles, for which a large number of RD patterns have been characterized 8 and the diffusion matrix often contains large off-diagonal terms. [9][10][11][12] Cross-diffusion effects are also known to be able to trigger convective motions around liquid interfaces in the absence of chemical reactions.…”

Amplitude equations for reaction-diffusion systems with cross diffusion

“…In general, cross-diffusion can modify any type of pattern, stationary, periodic or chaotic, and can even induce diffusive instability, Turing or wave [2,3]. Recent experiments [4][5][6] on the Belousov-Zhabotinsky reaction in a reverse microemulsion (BZ-AOT system [7]) have revealed that significant cross-diffusion takes place in this system, and model calculations [5] suggest that cross-diffusion effects should be large enough to affect BZ-AOT patterns.…”