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“Black spots” in a surfactant-rich Belousov–Zhabotinsky reaction dispersed in a water-in-oil microemulsion system
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View: Figures


Image of FIG. 1.
FIG. 1.

Turing patterns in the BZ-AOT system at different concentrations of . Stationary patterns are in the middle column. Left column shows transient patterns that first emerge in the reactor. Parameters: , , , , , 0.18, (c, d) 0.24, (e, f) 0.3. All concentrations are for the aqueous pseudophase (not the total volume of microemulsion). Frame . Two-dimensional FFTs of the snapshots in the middle column are shown in the right column. Two images of the FFT correspond to two different scaling factors (1 and 2) of the FFT and allow one to see the FFT at different contrast levels. White dots correspond to FFT peaks in the allowable contrast range, 1 (black)–256 (white).

Image of FIG. 2.
FIG. 2.

(a) Conductivity of an AOT microemulsion loaded with the reactants of the BZ reaction as a function of droplet fraction at two different . Concentrations: , , . (b, c) Time series of bulk oscillations in a CSTR recorded as absorption at (arbitrary wavelength in the absorption band of the oxidized catalyst) in a square cell. Compositions of the BZ-AOT system as in Fig. 1; panels (b) and (c) correspond to (a, b) and (e, f) in Fig. 1, respectively. Period of oscillations . (d) Delay time [see (c)] vs . is dependent on stirring rate and thus can vary slightly from experiment to experiment.

Image of FIG. 3.
FIG. 3.

Dependence of wavelength of Turing patterns on (a) [MA] at and (b) at . Other parameters: , , , , (b) (open triangles) and (closed triangles).

Image of FIG. 4.
FIG. 4.

Evolution of a Turing pattern in the BZ-AOT system. (a) [corresponds to in (e)], (b) , (c) after emergence of the first pattern. Frame . (d) Time dependence of the wavelength of Turing patterns. (e) Time series of bulk oscillations in a CSTR recorded as absorption at . Parameters: , , , , , .

Image of FIG. 5.
FIG. 5.

Black spots in the BZ-AOT system at large for (a, c) specially washed glass windows and filtered microemulsion; (b, d) microemulsion without filtration and cleaning of window surfaces. Parameters: , , , , , . Frame sizes are . Time lapse between snapshots (a) and (c), as well as between (b) and (d), is .

Image of FIG. 6.
FIG. 6.

Coexistence of black spots with (a) black reduction waves and (b) white oxidation waves at different times. (c) Space-time dependence at the gray line in snapshots (a) and (b). Arrows in plot (c) indicate times at which snapshots (a) and (b) were taken. Time lapse between snapshots (a) and (b) is . Parameters: , , , , , . Frame sizes: (a), (b) , (c) . Wave velocity for black waves [first waves in (c)], for white waves in (b), and for last set of waves in (c). Arrows in (a) and (b) indicate direction of wave propagation.

Image of FIG. 7.
FIG. 7.

Stationary (a), (b) and oscillatory (c), (d) Turing patterns in the BZ-AOT system at (a) , (b) , (c) , (d) after the emergence of the pattern. (e) Space-time dependence at the gray line in snapshot (b). Arrows in plot (e) correspond to snapshots (a)–(d). Parameters: , , , , , . Frame sizes: (a)–(d) , (e) .

Image of FIG. 8.
FIG. 8.

(a) Oscillations in 0D system (10) and (11) with , , , , and (curve 1), 0.0097 (curve 2); . The same shape of oscillations as in curve (2) is obtained at and . (b) Curves 1 and 2 are nullclines for Eqs. (10) and (11), respectively, with parameters: , , , , and (curve 3, trajectory of large amplitude oscillations), 0.01 (curve 4, trajectory of small amplitude oscillations). Steady state (cross point of curves 1 and 2) is inside the loops 3 and 4. (c) Phase diagram of system (10) and (11) in logarithmic coordinates. Parameters , , , . SS is steady state with fully oxidized catalyst, means instabilities. Curve (1) (white squares) corresponds to the onset of Turing instability, curve (2) to the onset of Hopf instability. Points of curve (2) are fitted by a linear trend line with slope . (d) Dispersion curves for system (10) and (11) with , , , , , . Curves (1) correspond to Fig. 10(a), and curves (2) to Fig. 10(b). Curves and are real part of eigenvalue, curves and are corresponding imaginary parts. Two horizontal dashes indicate half of the imaginary part at . Two vertical dashes indicate half of [ has a maximum at ].

Image of FIG. 9.
FIG. 9.

Turing patterns in model (10) and (11). (a) Parameters: , , , , , , , , . At these parameters, and , thus the system exhibits pure Turing instability; . (b) An increase in by increasing to 100, transforms black spots in (a) into stripes. (c) Localized Turing spot. Parameters: , , , , , , ; , . , . All eigenvalues have negative real part at all wave numbers . Stationary single spot emerges only after a large local perturbation of the steady state, at the center of the square area, where is the steady state value of . (d) Increasing to by decreasing to 22 leads to the slow spreading of Turing spots, which finally occupy the entire area; all other parameters as in (c).

Image of FIG. 10.
FIG. 10.

Space-time plot for oscillatory Turing patterns in 1D. Model parameters: , , , , , , , 1.78, (b) 1.7; 3.2, (b) 2.72. White corresponds to maximum of activator and black to minimum. Total 0.6, (b) 1.08.

Image of FIG. 11.
FIG. 11.

FFT spectra for time series of 1D oscillatory Turing patterns shown in Fig. 10 for 3.2, (b) 2.9, (c) 2.8, (d) 2.72. Bold solid and thin dotted lines in (b) and (c) correspond to different spatial points.

Image of FIG. 12.
FIG. 12.

Oscillatory Turing patterns in 2D for model (10) and (11). Parameters: , , , , , . For , and (between snapshots); one full period , , . For , , and ( a period), , .

Image of FIG. 13.
FIG. 13.

(a) One-dimensional Reduction waves in model (10) and (11). Bold line is catalyst ; thin dotted line is activator . Arrow shows direction of wave propagation. At initial moment of time, left edge of the segment (with zero flux boundary conditions) was perturbed. Parameters: , , , , , , (similar waves are obtained at ). The system is close to the subcritical Hopf bifurcation. At these parameters, at , while at , at . (b) Homogeneous large-amplitude oscillations on a segment of length 80 after homogeneous large-amplitude perturbation ; , , . Oscillations are the same as in 0D case.

Image of FIG. 14.
FIG. 14.

White Turing spots at large . , , , , , , . (a, b) , , 1D case, . For (c)–(g), , 17, 20, 45, and 300, respectively, , (h) , . In all cases, vertical thin line in the center is perturbed initially.

Image of FIG. 15.
FIG. 15.

Stationary Turing patterns in model (10) and (11) in the oxidized steady state of the system. Parameters: , , , , , (as in Fig. 8), . (a)–(c) small random initial perturbation ; , ; (a, b) (light line) and (dark line) profiles at and , respectively; (c) profiles at 75, (2) 79, (3) 90, (4) 135, (5) 375, is shifted down by (1) 0, (2) 0.01, (3) 0.02, (4) 0.1, and (5) 0.2. Small amplitude oscillations at each spatial point with a period of 2.14 gradually die and at first Turing patterns [(shown in (a)] start to emerge. (d) Large initial perturbation at one edge of the segment. Horizontal lines in (d) indicate steady states. Wavelength 8.64, (b) 12.3; (d) 14.5.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: “Black spots” in a surfactant-rich Belousov–Zhabotinsky reaction dispersed in a water-in-oil microemulsion system