sodium-bromate and malonic-acid

Coupled chemical oscillators are usually studied with symmetric coupling, either between identical oscillators or between oscillators whose frequencies differ. Asymmetric connectivity is important in neuroscience, where synaptic strength inequality in neural networks commonly occurs. While the properties of the individual oscillators in some coupled chemical systems may be readily changed, enforcing inequality between the connection strengths in a reciprocal coupling is more challenging. We recently demonstrated a novel way of coupling chemical oscillators, which allows for manipulation of individual connection strengths. Here we study two identical, pulse-coupled Belousov-Zhabotinsky (BZ) oscillators with unequal connection strengths. When the pulse perturbations contain KBr (inhibitor), this system exhibits simple out-of-phase and complex oscillations, oscillatory-suppressed states as well as temporally periodic patterns (N : M) in which the two oscillators exhibit different numbers of peaks per cycle. The N : M patterns emerge due to the long-term effect of the inhibitory pulse-perturbations, a feature that has not been considered in earlier works. Time delay was previously shown to have a profound effect on the system's behaviour when pulse coupling was inhibitory and the coupling strengths were equal. When the coupling is asymmetric, however, delay produces no qualitative change in behaviour, though the 1 : 2 temporal pattern becomes more robust. Asymmetry in instantaneous excitatory coupling via AgNO3 injection produces a previously unseen temporal pattern (1 : N patterns starting with a double peak) with time delay and high [AgNO3]. Numerical simulations of the behaviour agree well with theoretical predictions in asymmetrical pulse-coupled systems.

Topics: Bromates; Bromides; Malonates; Models, Neurological; Nerve Net; Periodicity; Phenanthrolines; Potassium Compounds; Silver Nitrate; Sodium Compounds; Sulfuric Acids; Synapses

We present an investigation of spiral waves pinned to circular and rectangular obstacles with different circumferences in both thin layers of the Belousov-Zhabotinsky reaction and numerical simulations with the Oregonator model. For circular objects, the area always increases with the circumference. In contrast, we varied the circumference of rectangles with equal areas by adjusting their width w and height h. For both obstacle forms, the propagating parameters (i.e., wavelength, wave period, and velocity of pinned spiral waves) increase with the circumference, regardless of the obstacle area. Despite these common features of the parameters, the forms of pinned spiral waves depend on the obstacle shapes. The structures of spiral waves pinned to circles as well as rectangles with the ratio w/h∼1 are similar to Archimedean spirals. When w/h increases, deformations of the spiral shapes are observed. For extremely thin rectangles with w/h≫1, these shapes can be constructed by employing semicircles with different radii which relate to the obstacle width and the core diameter of free spirals.

Topics: Bromates; Diffusion; Malonates; Models, Chemical; Phenanthrolines; Sodium Compounds; Sulfuric Acids

In the present study, a novel gel with a semi-interpenetrating polymer network (semi-IPN) that undergo the Belousov-Zhabotinsky (BZ) reaction without the addition of a strong acid (HNO3 or H2SO4) was developed. The required concentrations of the BZ substrates, sodium bromate (NaBrO3) and malonic acid (MA), under these conditions were higher than under the normal BZ reaction conditions, involving the addition of a strong acid. The period of the BZ reaction with the novel gel (semi-IPN BZ gel) decreased with increasing concentrations of NaBrO3 and MA. Moreover, the connection of the semi-IPN BZ gel to a conventional BZ gel facilitated the reaction in the latter through the propagation of the intermediates from the former to the latter. The BZ reaction stopped when the conventional BZ gel was disconnected from the semi-IPN BZ gel. These results demonstrate that the BZ reaction in the conventional BZ gel underwent on-off switching, controlled by its attachment to the semi-IPN BZ gel. This on-off switching mechanism would be valuable in controlling actuators and robots without strong acids.

Topics: Bromates; Gels; Malonates; Microscopy, Video; Polymers; Sodium Compounds; Temperature

We succeeded in measuring the generative force of a self-oscillating polymer gel in an aqueous solution comprising the three substrates of the Belousov-Zhabotinsky (BZ) reaction (malonic acid, sodium bromate, and nitric acid) under constant temperature. In this study, we developed an apparatus with a microforce sensor for measuring the generative force of small-sized gels (1 mm(3)). The self-oscillating polymer gel directly converts the chemical energy of the BZ reaction into mechanical work. It was determined that the generative force of the self-oscillating gel was 972 Pa, and the period of self-oscillation was 480 s at 18 °C. We demonstrated that the generative force of the gel was about a hundredth the generative force of a muscle in the body. We analyzed the time dependence of the color change in the self-oscillating polymer gel. The color of the gel changed periodically owing to the cyclic change in the redox state of the Ru moiety, induced by the BZ reaction. The peaks of the waveforms of the generative force and color change were almost identical. This result showed that the generative force was synchronized with the periodical change in the oxidation number of the Ru catalytic moiety in the gel. To understand a theoretical basis for the generative force of a self-oscillating gel, we considered a general theory that is based on the volume phase transition of gel and the two-parameter Oregonator model of the BZ reaction.

Topics: Acrylamides; Acrylic Resins; Alkanesulfonates; Bromates; Catalysis; Gels; Malonates; Nitric Acid; Organometallic Compounds; Sodium Compounds

We have developed self-oscillating polymers and gels as novel biomimetic materials by utilizing an oscillating reaction, known as the Belousov-Zhabotinsky (BZ) reaction. The self-oscillating polymer gel is composed of a poly(N-isopropylacrylamide) (PNIPAAm) network in which the catalyst for the BZ reaction is covalently immobilized. Under the coexistence of the reactants, the gel undergoes spontaneous cyclic swelling-deswelling changes without any on-off switching of external stimuli. In order to induce self-oscillation while maintaining a larger amplitude at higher temperatures and around body temperature for potential applications to biomaterials, etc., here we prepared a self-oscillating gel composed of a thermosensitive N,N'-ethylmethylacrylamide (EMAAm) polymer exhibiting a higher LCST than that of the NIPAAm polymer. The self-oscillating behavior of the poly(EMAAm-co-Ru(bpy)(3)) gel was investigated by comparing against gels composed of a thermosensitive NIPAAm polymer with a lower LCST or non-thermosensitive N,N'-dimethylacrylamide (DMAAm) polymer. The design concept of self-oscillation at higher temperatures without a decrease in swelling-deswelling amplitude was demonstrated by utilizing a thermosensitive polymer exhibiting a higher LCST.

Topics: Acrylamides; Acrylic Resins; Biomimetic Materials; Bromates; Catalysis; Cerium; Hydrogels; Kinetics; Malonates; Mechanical Phenomena; Nitric Acid; Organometallic Compounds; Oxidation-Reduction; Phase Transition; Polymers; Sodium Compounds; Sulfates; Temperature; Transition Temperature; Water

Belousov-Zhabotinsky (BZ) reaction-induced mechanical oscillation of poly(N-isopropylacrylamide) (PNIPAM) gel particles was investigated by the systematic variation of BZ substrate concentrations. The correlation between the dynamic behavior and substrate concentrations was presented in a ternary phase diagram. Both oscillatory and steady-state regimes exist on the phase diagram and are separated by a high-frequency oscillation band. Dependence of oscillation frequency and induction time on the substrate concentrations was also studied. To achieve size uniformity, these PNIPAM gel particles with covalently bound tris(bipyridyl)ruthenium(II) were synthesized via the coordination chemistry between a ruthenium complex and the monodispersed PNIPAM gel particles bearing bipyridine ligands.

Topics: 2,2'-Dipyridyl; Acrylamides; Acrylic Resins; Bromates; Catalysis; Colloids; Gels; Malonates; Models, Biological; Models, Chemical; Molecular Structure; Organometallic Compounds; Oscillometry; Particle Size; Phase Transition; Ruthenium; Sodium Compounds

The propagation of chemical waves in the photosensitive Belousov-Zhabotinsky (BZ) reaction was investigated using an excitable field in the shape of a circular ring or figure "8" that was drawn by computer software and then projected on a film soaked with BZ solution using a liquid-crystal projector. For a chemical wave in a circular reaction field, the shape of the chemical wave was investigated depending on the ratio of the inner and outer radii. When two chemical waves were generated on a field shaped like a figure "8" (one chemical wave in each circle) as the initial condition, the location of the collision of the waves either was constant or alternated depending on the degree of overlap of the two circular rings. These experimental results were analyzed on the basis of a geometrical discussion and theoretically reproduced on the basis of a reaction-diffusion system using a modified Oregonator model. These results suggest that the photosensitive BZ reaction may be useful for creating spatio-temporal patterns depending on the geometric arrangement of excitable fields.

Topics: 2,2'-Dipyridyl; Bromates; Bromides; Computer Simulation; Coordination Complexes; Light; Malonates; Models, Chemical; Photochemistry; Potassium Compounds; Sodium Compounds; Sulfuric Acids; Temperature; Time Factors