Chemical micro-oscillators based on the Belousov–Zhabotinsky reaction

The results of studies on the development of micro-oscillators (MOs) based on the Belousov –Zhabotinsky (BZ) oscillatory chemical reaction are integrated and systematized. The mechanisms of the BZ reaction and the methods of immobilization of the catalyst of the BZ reaction in micro-volumes are briefly discussed. Methods for creating BZ MOs based on water microdroplets in the oil phase and organic and inorganic polymer microspheres are considered. Methods of control and management of the dynamics of BZ MO networks are described, including methods of MO synchronization. The prospects for the design of neural networks of MOs with intelligent-like behaviour are outlined. Such networks present a new area of nonlinear chemistry, including, in particular, the creation of a chemical ‘computer’.

The bibliography includes 250 references.

Distance dependent types of coupling of chemical micro-oscillators immersed in a water-in-oil microemulsion

A system of micro-spheres immersed in a water-in-oil microemulsion (ME) is studied both theoretically and experimentally.

Synthesis of Non-Uniform Functionalized Amphiphilic Block Copolymers and Giant Vesicles in the Presence of the Belousov-Zhabotinsky Reaction

Giant vesicles with several-micrometer diameters were prepared by the self-assembly of an amphiphilic block copolymer in the presence of the Belousov-Zhabotinsky (BZ) reaction. The vesicle is composed of a non-uniform triblock copolymer synthesized by multi-step reactions in the presence of air at room temperature. The triblock copolymer contains poly(glycerol monomethacrylate) (PGMA) as the hydrophilic block copolymerized with tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3), which catalyzes the BZ reaction, and 2-hydroxypropyl methacrylate (HPMA) as the hydrophobic block. In this new approach, the radicals generated in the BZ reaction can activate a reversible addition-fragmentation chain transfer (RAFT) polymerization to self-assemble the polymer into vesicles with diameters of approximately 3 µm. X-ray photoelectron spectroscopy (XPS) measurements demonstrated that the PGMA-b-Ru(bpy)3-b-PHPMA triblock copolymer is brominated and increases the osmotic pressure inside the vesicle, leading to micrometer-sized features. The effect of solvent on the morphological transitions are also discussed briefly. This BZ strategy, offers a new perspective to prepare giant vesicles as a platform for promising applications in the areas of microencapsulation and catalyst support, due to their significant sizes and large microcavities.

Amoeba-like self-oscillating polymeric fluids with autonomous sol-gel transition

In the field of polymer science, many kinds of polymeric material systems that show a sol-gel transition have been created. However, most systems are unidirectional stimuli-responsive systems that require physical signals such as a change in temperature. Here, we report on the design of a block copolymer solution that undergoes autonomous and periodic sol-gel transition under constant conditions without any on–off switching through external stimuli. The amplitude of this self-oscillation of the viscosity is about 2,000 mPa s. We also demonstrate an intermittent forward motion of a droplet of the polymer solution synchronized with the autonomous sol-gel transition. This polymer solution bears the potential to become the base for a type of slime-like soft robot that can transform its shape kaleidoscopically and move autonomously, which is associated with the living amoeba that moves forward by a repeated sol-gel transition.

Most polymeric materials that show sol-gel transitions are unidirectional and stimuli-responsive systems. Here the authors show a block copolymer solution that undergoes autonomous and periodic sol-gel transitions under constant conditions.

Determination of the diffusion coefficient of hydrogen ion in hydrogels

The role of diffusion in chemical pattern formation has been widely studied due to the great diversity of patterns emerging in reaction-diffusion systems, particularly in H⁺-autocatalytic reactions where hydrogels are applied to avoid convection. A custom-made conductometric cell is designed to measure the effective diffusion coefficient of a pair of strong electrolytes containing sodium ions or hydrogen ions with a common anion. This together with the individual diffusion coefficient for sodium ions, obtained from PFGSE-NMR spectroscopy, allows the determination of the diffusion coefficient of hydrogen ions in hydrogels. Numerical calculations are also performed to study the behavior of a diffusion-migration model describing ionic diffusion in our system. The method we present for one particular case may be extended for various hydrogels and diffusing ions (such as hydroxide) which are relevant e.g. for the development of pH-regulated self-healing mechanisms and hydrogels used for drug delivery.

A surface-grafted thermoresponsive hydrogel in which the surface structure dominates the bulk properties

A surface-grafted hydrogel was successfully synthesized by immobilization of the ATRP initiator at the surface region of the gel and the subsequent ARGET ATRP step.

Multiblock copolymers exhibiting spatio-temporal structure with autonomous viscosity oscillation

Here we report an ABA triblock copolymer that can express microscopic autonomous formation and break-up of aggregates under constant condition to generate macroscopic viscoelastic self-oscillation of the solution. The ABA triblock copolymer is designed to have hydrophilic B segment and self-oscillating A segment at the both sides by RAFT copolymerization. In the A segment, a metal catalyst of chemical oscillatory reaction, i.e., the Belousov-Zhabotinsky (BZ) reaction, is introduced as a chemomechanical transducer to change the aggregation state of the polymer depending on the redox states. Time-resolved DLS measurements of the ABA triblock copolymer confirm the presence of a transitional network structure of micelle aggregations in the reduced state and a unimer structure in the oxidized state. This autonomous oscillation of a well-designed triblock copolymer enables dynamic biomimetic softmaterials with spatio-temporal structure.

Self-oscillating AB diblock copolymer developed by post modification strategy

We prepared AB diblock copolymer composed of hydrophilic poly(ethylene oxide) segment and self-oscillating polymer segment. In the latter segment, ruthenium tris(2,2'-bipyridine) (Ru(bpy)3), a catalyst of the Belousov-Zhabotinsky reaction, is introduced into the polymer architecture based on N-isopropylacrylamide (NIPAAm). The Ru(bpy)3 was introduced into the polymer segment by two methods; (i) direct random copolymerization (DP) of NIPAAm and Ru(bpy)3 vinyl monomer and (ii) post modification (PM) of Ru(bpy)3 with random copolymer of NIPAAm and N-3-aminopropylmethacrylamide. For both the diblock copolymers, a bistable temperature region (the temperature range; ΔTm), where the block copolymer self-assembles into micelle at reduced Ru(bpy)3(2+) state whereas it breaks-up into individual polymer chain at oxidized Ru(bpy)3(3+) state, monotonically extends as the composition of the Ru(bpy)3 increases. The ΔTm of the block copolymer prepared by PM is larger than that by DP. The difference in ΔTm is rationalized from the statistical analysis of the arrangement of the Ru(bpy)3 moiety along the self-oscillating segments. By using the PM method, the well-defined AB diblock copolymer having ΔTm (ca. 25 °C) large enough to cause stable self-oscillation can be prepared. The periodic structural transition of the diblock copolymer in a dilute solution ([Polymer] = 0.1 wt. %) is closely investigated in terms of the time-resolved dynamic light scattering technique at constant temperature in the bistable region. A macroscopic viscosity oscillation of a concentrated polymer solution (15 wt. %) coupled with the periodic microphase separation is also demonstrated.

A modular approach to self-oscillating polymer systems driven by the Belousov–Zhabotinsky reaction

This review explores the principle, modular construction, integral control and engineering aspects of self-oscillating polymer systems driven by the Belousov–Zhabotinsky reaction.

Control of swelling–deswelling behavior of a self-oscillating gel by designing the chemical structure

To improve the self-oscillating gel we have developed so far, the ternary self-oscillating polymer and the gel were newly prepared. Their phase transition and self-oscillating behaviors were investigated considering potential applications.

Spatiotemporal control of synergistic gel disintegration consisting of boroxole- and glyco-based polymers via photoinduced proton transfer

We demonstrate here a local- and remote-control of gel disintegration by using photoinduced proton transfer chemistry of photoacid generator (PAG). The gels were prepared by simply mixing two polymers, poly(N-isopropylacrylamide-co-5-methacrylamido-1,2-benzoxaborole) (P(NIPAAm-co-MAAmBO)) and poly(3-gluconamidopropyl methacrylamide) (PGAPMA) via the synergistic interaction of benzoxaborole and diol groups. The o-nitrobenzaldehyde (o-NBA) was then loaded into the gel as a PAG. The benzoxaborole-diol interaction was successfully disintegrated upon UV irradiation due to the local pH decrease inside the gel. When the gel was irradiated to a specific gel region, the synergistic interactions were disintegrated only at the exposed region. Of special interest is that the whole material eventually transitioned from gel to sol state, as the generated protons diffused gradually toward the nonilluminated region. The ability of the proposed gel-sol transition system via photoinduced proton diffusion may be beneficial for not only prompt pH changes within the gel but also the design of predictive and programmable devices for drug delivery.