Belousov-Zhabotinsky Reagent Research Articles

Co-Complexes-Based Self-Oscillating Gels Driven by the Belousov-Zhabotinsky Reaction.

We report the synthesis of novel cobalt complexes-based catalysts designed for the oscillatory Belousov-Zhabotinsky (BZ) reaction. For the first time, we introduce cobalt complex-based self-oscillating gels that demonstrate autonomous color oscillations within a BZ reagent solution, functioning without the need for any external stimuli. We created acrylamide-based self-oscillating gels containing immobilized tris(2,2'-bipyridine)cobalt(II) or tris(1,10-phenanthroline)cobalt(II) complexes and gels containing covalently bound (5-acrylamido-1,10-phenanthroline)bis(2,2'-bipyridine)cobalt(II), (5-acrylamido-1,10-phenanthroline)bis(1,10-phenanthroline) cobalt(II), or tris(5-acrylamido-1,10-phenanthroline)cobalt(II) complexes. When the BZ reaction takes place within the gels, it results in the observation of moving chemical waves and reversible color changes. We believe that Co-complexes-based self-oscillating gels have potential applications in the design of soft actuators and chemical devices for signal processing.

Belousov–Zhabotinsky Hydrogels: Relationship between Hydrogel Structure and Mechanical Response

The novel chemo-mechanical feedback within autonomic Belousov–Zhabotinsky (BZ) hydrogels mimics the complex adaptivity found in natural systems and inspires soft device concepts for chemical computing, sensing, and actuation. A quantitative relationship between the dynamic response, strain, BZ reagents, and hydrogel constituents, however, is still evolving due to a limited material suite. Using a modular synthesis strategy for free-radical BZ-catalyst monomers, we compare the impact of cross-linker, catalyst, and total polymer concentration on the cyclic strain of PNIPAm- and PAAm-based BZ hydrogels. The oscillator strain of the hydrogel in the BZ solution relative to the difference between equilibrium swelling of the fully oxidized and reduced states highlights the trade-off between BZ reaction kinetics, hydrogel elasticity, and catalyst concentration. For a PNIPAm-based BZ gel, a maximum strain of 20% occurs at a total polymer and [Ru] concentration of 4.8 ± 0.5 μg/mm3 and 1.5 mM due to a complementary ...

Modeling the Chemo-mechanical Behavior of Reactive Polymer Gels

ABSTRACTWe consider a theoretical model of a reactive polymer gel in which the reaction can proceed in an oscillatory regime and generate traveling chemical waves accompanied by waves of local swelling-deswelling. This type of gel could be used for fabricating chemo-mechanical devices with self-sustained rhythmic action, and gel-based pumps. We assume that the Belousov-Zhabotinsky (BZ) reaction takes place in the reactive gel. The BZ reaction generates periodic reduction-oxidation (redox) changes of a metal catalyst covalently bonded to a hydrogel that is immersed in a solution containing the rest of the BZ reagents. The redox changes in the metal affect the polymer-solvent interactions, resulting in variations in the gel volume. The self-oscillation of the gel volume, and the traveling waves of local swelling in a hydrogel with the BZ reaction have been experimentally observed by Yoshida and co-workers. To describe the system theoretically, we employ the Oregonator model of the BZ reaction, and the two-fluid model of gel dynamics. Propagation of one-dimensional wave trains through the reactive gel is simulated. The structure of the traveling swelling-deswelling waves is studied.

Oscillations and turbulence induced by an activating agent in an active medium.

An excitable Belousov-Zhabotinsky reagent becomes oscillatory above a threshold of methanol concentration [Me]. The oscillation period decreases with increasing [Me]. A model describes these observations quantitatively. In a spatiotemporal setup, a [Me] gradient causes waves with spatially varying properties; this leads to wave breaks that end up in turbulence, both in experiments and in simulations with partial differential equations.

Oxygen-induced wavefront instabilities and disorder in the Belousov–Zhabotinsky reaction

Wavefront instabilities leading to spatiotemporal disorder in a convection-free and horizontally homogeneous Ru(bpy) 3 2+-catalyzed Belousov–Zhabotinsky reagent had previously been measured and simulated. Necessary conditions in a 20% O 2 atmosphere (air) were: high light intensities ( I>150 mW/m 2) and low catalyst concentrations (⩽1 mM). Here, we show that at sufficiently high O 2 concentrations, comparable instabilities and disorder appear even in the dark or at high (⩾1 mM) catalyst concentrations. In contrast, in the ferroin-catalyzed reagent such dynamic processes are not observed at any value of I in air, although they do occur — independently of I — at sufficiently high O 2 concentrations.

Resonant pattern formation in achemical system

A periodic force applied to a nonlinear pendulum can cause the pendulum to become entrained at a frequency that is rationally related to the applied frequency, a phenomenon known as frequency-locking1. A recent theoretical analysis showed that anarray of coupled nonlinear oscillators can exhibit spatial reorganization when subjected to external periodic forcing2. We present here experimental evidence that reaction–diffusion processes, which govern pattern evolution and selection in many chemical and biological systems3, can also exhibit frequency-locking phenomena. For example, periodic optical forcing of the light-sensitive Belousov–Zhabotinsky (BZ) reaction transforms a rotating spiral wave4 to a labyrinthine standing-wave pattern (Fig. 1). As the forcing frequency is varied, we observe a sequence of frequency-locked regimes, analogous to the frequency-locked ‘tongues’ of a driven nonlinear pendulum, except that in the reactor different frequencies correspond to different spatial patterns. Resonant interactions leading to standing-wave patternshave not been observed previously in chemical or biological media, but periodic forcing (such as circadian rhythm) is abundant in nature and may lead to similar pattern-forming phenomena.The reaction occurs in a 0.4-mm-thick porous membrane disk that is placed between two reservoirs (I and II) which are continously refreshed with BZ reagents. The region shown is a 13 × 13 mm section of the 25-mm-diameter reactor. The patterns in the membrane are determined from light absorption measurements at 450 nm. In the perturbed region, light of 0.2 W m−2intensity in the spectral range 430–470 nm is periodically switched on for 6 s and then off for 13 s. Spatially uniform illumination is achieved using a video projector (Sanyo PLC-220N) calibrated by measuring light reflected from a scatter plate and then adjusting each pixel to have the same intensity. The concentrations of thechemicals in reservoirs I and II are: [malonic acid]I = 0.22 M, [BrO3−]I = 0.046 M, [BrI−] = 0.2 M, [H2SO4]I = 0.8 M, [Ru(bpy)32+]II = 1.0 mM, [H2SO4]II = 0.8 M, [BrO3−]II = 0.184 M (here bpy indicates 2,2′-bipyridine). The volume of each reservoir is 10 ml. The flow rate in reservoir I is 20 ml h−1; in reservoir II, 5 ml h−1. The system is maintained at a temperature of 23 °C.

Spiral waves on circular and spherical domains of excitable medium

The evolution of spiral waves on a circular domain and on a spherical surface is studied by numerical integration of a reaction-diffusion system. Two different asymptotic regimes are observed for both domains. The first regime is a rigid rotation of an excitation wave around the symmetry axis of the domain. The second one is a compound rotation including a drift of the rotation center of the spiral wave either along the boundary of the disk or along the equator of the sphere. In this case the shape of the wave and its rotation velocity are periodically changing in time. Simplified analytical estimates are presented to describe the rigid rotation. The computational results are complemented by experimental observation of spiral wave evolution in a small circular domain of a thin layer of Belousov-Zhabotinsky reagent.

Refraction of chemical waves propagating in modified membranes

Different possibilities to perform refraction experiments with chemical waves propagating in membranes modified with a fixed catalyst of the oscillatory Belousov–Zhabotinsky (BZ) reaction were investigated. Two methods to modify the velocity of chemical waves were developed. According to the first, barium sulfate was precipitated in certain regions of the modified membrane to decrease the wave velocity. The second method, which is more reproducible, applies barrier membranes, such as plastic foils or Nuclepore porous membranes, placed between the catalyst membrane and the reservoir of the other BZ reagents. Wave velocity maps calculated from the experiments show that the waves are slower in membrane regions which are separated from the reservoir by a barrier. When water evaporation from the membrane was allowed an inverse velocity map can be observed after some hours. A qualitative explanation of these observations is also presented. Finally, experiments made in an oxygen-free atmosphere prove that the wave refraction phenomena reported here are not caused by oxygen from the air.

Disordered waves in a homogeneous, motionless excitable medium

EXCITABLE media are physical, chemical or biological systems in which energy dissipation in disturbed regions is compensated by energy supply1–4, so that the media can support waves without attenuation. Well-known examples are nervous tissue, heart muscle, retinae, aggregating amoebae and the autocatalytic Belousov–Zhabotinsky (BZ) reaction. Most familiar in such systems are periodic target and spiral waves, but a number of simulations5–11 have suggested that disordered waves can also occur in a homogeneous and motionless excitable medium. In all experimental observations reported so far, however, hydrodynamic flow12,13 or inhomogeneities14–15 were necessary to induce disorder. Here we present experimental evidence for disordered chemical waves in a convection-free and homogeneous medium, a gel containing a light-sensitive BZ reaction mixture. We find instabilities transverse to the wavefront ('ripples'), wave breakup leading to aperiodic spiral formation, labyrinthine structures, and erratic motion of non-spiralling wave fragments. The formal analogy of the BZ reagent with other excitable media suggests that this disordered behaviour may be generic.

Rotating Spiral Waves Created by Geometry

The Belousov-Zhabotinsky reagent and numerical simulations were used to show that under high-frequency stimuli, rotating spiral waves can be initiated in a homogeneous excitable medium in the vicinity of domain boundaries or inexcitable barriers with sharp corners.

Pattern formation in a two-dimensional reaction-diffusion system with a transversal chemical gradient

In a thin layer of chromatographic silica gel saturated by Belousov-Zhabotinsky reagent, in which a transversal gradient of oxygen is set up, chemical waves appear first only at the bottom of the layer. Later, waves are also induced at the top of the layer. The top waves propagate almost independently, but weakly interact with the bottom waves. As a result, fronts with unusual sawtooth- or staircase-like geometry are formed.

Recipes for Belousov-Zhabotinsky reagents

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRecipes for Belousov-Zhabotinsky reagentsWolfgang Jahnke and Arthur T. Winfree Cite this: J. Chem. Educ. 1991, 68, 4, 320Publication Date (Print):April 1, 1991Publication History Received3 August 2009Published online1 April 1991Published inissue 1 April 1991https://doi.org/10.1021/ed068p320RIGHTS & PERMISSIONSArticle Views2435Altmetric-Citations19LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (3 MB) Get e-Alerts Get e-Alerts

Helical organizing centers in excitable media

Numerical simulations of three distinct models of excitable media (two-variable Oregonator, with both variables diffusing equally; and piecewise linear A and B kinetics, with only the propagator variable diffusing) are used here to investigate the dynamics of scroll filaments, with emphasis on the role of twist. In all three models, initially uncurved filaments uniformly twisted more than a threshold amount 'sproing' into radially expanding helices, some of which stabilize at finite radius. By monitoring the evolution of these helices with a differential geometry 'tool kit', we attempt to discern the presumed causal dependence of filament motion (resolved into velocities along the normal and binormal directions of the local Frenet frame) and rotor spin rate, on local filament geometry (curvature and torsion) and twist. Twist can reverse the direction of normal velocity from that seen in untwisted scroll rings; binormal velocity is either reversed (A kinetics), abolished (B kinetics), or engendered (Oregonator). In all cases twist increased spin rate, as predicted by theory. Our efforts to perceive a functional dependence of the dynamical variables on filament geometry and twist have met with limited success, but we believe our attempts have uncovered some useful methodology and exposed some pitfalls relevant to any such investigation. The existence and properties of a novel class of stable organizing centers, as well as the existence of a threshold of twist for their induction, should be of interest to theorists. In addition, our findings here based on models suggest new phenomena to look for in various excitable media, such as the Belousov–Zhabotinsky reagent or heart muscle.

Interaction of chemical waves in a thin layer of microheterogeneous gel with a transversal chemical gradient

Chemical-wave propagation is investigated in a thin layer of chromatographic silica gel saturated by Belousov—Zhabotinsky reagent. Due to a transversal gradient of oxygen, waves first appear only at the bottom of the layer. Later, waves are induced at the top which propagate almost independently but show weak interaction with the bottom waves by forming fronts with unusual saw-tooth or staircase-like geometry.

Diversity of three-dimensional chemical waves

The propagation of spiral waves in the Belousov-Zhabotinsky (BZ) reaction has been extensively investigated. The aim of this paper is to show the diversity of phenomenon in the three-dimensional BZ reagent with the aid of photographs of the evolving structures, not all of which have been studied mathematically. The most frequent observed wave forms are simple scrolls and toroidal scrolls; a brief discussion of the existence of toroidal scroll solution to the eikonal equation in three dimensions is presented.

Chemical vortex dynamics in three-dimensional excitable media

A dynamical system that can be provoked by a small stimulus to execute a large transient excursion before returning to the original state is called 'excitable'. In the Belousov–Zhabotinsky (BZ) reagent1 such excitation propagates as a travelling pulse of oxidative activity; leaving a point source, it resembles a closed spherical surface. Activity in excitable media can also be self-organized, independent of any recent stimulus. Wavefronts in cross-section then resemble a spiral emanating from a central pivot. In three dimensions the pivot points form a line, a vortex filament, that typically closes in a slowly shrinking 'scroll ring' (Fig. l)2–4. Here we report the results of monitoring this shrinkage quantitatively both in the BZ reagent and in the Oregonator model, leading to the confirmation of mathematical arguments that derive the filament's motion from its local curvature5–8. By additionally observing the predicted rapid unwinding of a coiled vortex filament9 we validate the reaction–diffusion theory of self-organized activity in such excitable media.

The Motion of Untwisted Untorted Scroll Waves in Belousov-Zhabotinsky Reagent

Rotating waves of activity are seen in various biological phenomena and in chemical mixtures. In thin layers of these media, the waves often appear as spirals spinning around a pivot point, but actually they are scroll-shaped waves rotating around curved filament in three-space. The filament about which the scroll rotates is not stationary, but rather moves through space until it achieves a stable configuration or disappears altogether. Some features of the temporal evolution of a planar scroll wave filament can be understood in terms of the simple equation N = Dkappa, where N is the velocity of the filament in the direction of its principal normal, kappa is the curvature of the filament, and D is the diffusion coefficient of the active chemical species. This equation of motion implies that a scroll ring shrinks in size and collapses in finite time, that an elongated spiral evolves into a symmetric spiral, and that an elongated target pattern becomes more symmetrical and vanishes in finite time. Characteristic times for these processes are estimated. In each case, good quantitative agreement is found between implications of the model and observations of scroll-wave evolution in shallow layers of the Belousov-Zhabotinsky reagent.

Experimental study of traveling waves and target patterns in oscillatory reacting media

Recent experimental work on is presented traveling waves and target patterns developing in oscillatory Belousov-Zhabotinsky reagents. It only deals with trigger waves and relaxation oscillations. Measurements have been made on (1) the dispersion relation of waves, (2) the statistical properties of centers and targets, (3) the wavefront and speed near the core of the pattern. Several unanticipated results are reported.

Dynamical simulations of twisted scroll rings in three-dimensional excitable media

Excitable media such as heart muscle and the Belousov-Zhabotinsky reagent harbor vortex-like sources of periodic wave activity. In three dimensions this vortex has been observed in vivo, in vitro, and in numero. It typically closes in a ring. Using a partial differential equation model of an excitable medium, we present the first computation of a topologically new vortex ring. The computations suggest distinctive properties whereby we may recognize this new organizing center in experiments with excitable media.

Singular filaments organize chemical waves in three dimensions: I. Geometrically simple waves

This is the first of a series of papers on the anatomy of three-dimensional dissipative structures in excitable media. The Belousov-Zhabotinsky reagent provides examples. We describe the propagation of chemical waves in such media first in terms of “phase” in a cycle of excitation and relaxation, then in terms of chemical concentration surfaces. Phase singularities are shown to arise in a natural way as ring-like filaments in three dimensions. We describe the known methods of creating singularities and the simplest wave structure organized by a singular filament: the experimentally demonstrated scroll ring.