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Various spatiotemporal patterns were created on the surface or in the body of cation-exchange resin beads which were loaded with the catalyst of the Belousov-Zhabotinsky (BZ) reaction. Either global oscillations (GO) or traveling waves (TW) and the switching between them were observed in the previous papers, but it was not clear how chemicals contribute to the reaction inside/around the BZ bead. In this paper, we scanned the electrical potential, E, from +1 to -1 V (negative scan) and then turned from -1 to +1 V (positive scan) to control the switching between GO and TW. We found that the electrical switching potential from TW to GO, ETG, and from GO to TW, EGT, depended on the scanning direction of E and the diameter of the bead, d. The present study suggests that the electrode-induced increase of the inhibitor, Br-, and the activator, HBrO2, around the BZ bead plays an important role in determining ETG and EGT.

Here, we investigated the oscillatory motion of a camphor boat on water to clarify how the dynamics of camphor concentration profile determines the period of oscillation. The boat, which was made of a plastic plate and a camphor disk, was glued below the plate at a distance from the edge. The dependence of oscillation period on temperature and viscosity of the water phase was measured in experiments. We reproduced the experimental results by calculating the period of oscillatory motion by considering the experimental values of physicochemical parameters describing the time evolution of camphor concentration profile and the friction acting on a boat, such as diffusion and dissolution rates of camphor, viscosity of the water phase, and the threshold concentration of camphor necessary to accelerate the boat from the resting state. The increase in the period of oscillatory motion at low temperatures was explained by the reduced dissolution rate of camphor into the water phase.

Self-motion of a camphor disk rotating inside a water chamber composed of two half-disks was investigated. The half-disks were joined along their diameter segments, and the distance between their midpoints (ds) was considered as the control parameter. Various types of camphor disk motions were observed depending on ds. When ds = 0, the chamber had a circular shape, so it was symmetric. A camphor disk showed either a clockwise (CW) or counterclockwise (CCW) rotation with the direction determined by its initial state. The symmetry of the chamber was broken for ds0. For moderate distances between the midpoints, a unidirectional orbital motion of the disk was observed. The preferred rotation direction was determined by the shape of the chamber, and it did not depend on the initial rotation direction. For yet larger ds, the unidirectional circular motion was no longer observed and the trajectory became irregular. A mathematical model coupling the camphor disk motion with the dynamics of the developed camphor molecular layer on water was constructed, and the numerical results were compared with the experimental results. The selection of motion type can be explained by considering the influence of camphor concentration on the disk trajectory through the surface tension gradient.

Two coupled polymer gels, showing volume oscillation caused by the Belousov-Zhabotinsky (BZ) reaction, were investigated to understand the system composed of mechanically coupled chemical oscillators. The two gels were connected with a movable plastic sheet in between and placed under constant compression. Synchronization between two identical gels occurred in a range of compression ratios. The phase difference between the two oscillating gels was not zero; instead, they showed alternate swelling-deswelling oscillations. Similar phenomena were also observed with gels of different sizes and natural oscillation periods. The experimental results suggest that a physical change in one gel can lead to a chemical change in the other and vice versa. These results were qualitatively reproduced by a mathematical model based on coupled chemical oscillators.

The oscillation of a polymer gel induced by the Belousov-Zhabotinsky (BZ) reaction was investigated under an external force composed of a square wave. The oscillation of the BZ reaction entrained to the periodic force and the features of this entrainment changed depending on the period and duty cycle of the square wave. The experimental results suggest that the change in the volume of the gel also gave feedback to the BZ reaction. The mechanism of entrainment is discussed in relation to the compression of the gel and the reaction-diffusion system in the BZ reaction.

We investigated the Marangoni flow around a camphor disk on water with the addition of sodium dodecyl sulfate (SDS). The flow velocity decreased with an increase in the concentration of SDS in the aqueous phase, and flow was hardly observed around the critical micelle concentration (cmc), because SDS reduced the driving force of Marangoni flow. However, the flow velocity increased with a further increase in the concentration of SDS. Thus, the Marangoni flow is maximally inhibited around the cmc of SDS. In this paper, we concluded that the regeneration of Marangoni flow originates from an increase in the dissolution rate of camphor into the SDS aqueous solution.

The synchronized self-motion of two camphor boats on polygonal water chambers was investigated. The two boats synchronously moved depending on the number of corners in the polygon by changing the distance between the two boats through the corners. We regard the self-motion of a camphor boat as an oscillator; i.e., one cycle on the polygonal chamber corresponds to 2pi. Phase-locked synchronization at a phase difference of 2pi/3, which corresponds to the length of one side of the chamber, was observed with a triangular chamber. Two types of synchronized motion at phase differences of pi/2 and pi, which correspond to the length of one and two sides of the chamber, respectively, were observed with a square chamber. These characteristic features of synchronized self-motion were qualitatively reproduced by a numerical calculation that regarded the surface tension as the driving force and the number of corners in the chamber as a velocity-regulating mechanism. We believe that the present system may be a simple model of synchronization which depends on the geometry of the system.

The self-motion of camphene on water was investigated as a simple example of an autonomous motor. When a camphene disk was floated on water in a small Petri dish as an isotropic system, intermittent motion (alternating between rapid motion and rest) was observed at the center of the Petri dish. The floating state of the camphene disk changed periodically in association with the intermittent motion. When a camphene disk connected to a plastic boat as an anisotropic system was floated on water, uniform motion was observed. The nature of this self-motion is discussed in relation to the floating state of the camphene disk depending on convection and the surface tension of the camphene layer as the driving force.

The self-motion of a camphor grain was investigated on a linear water route. The oscillatory motion along the water route was maintained for ca. 15 cycles. The driving force is discussed in relation to a rhythmic change in the surface tension, which depends on the surface concentration of the camphor layer. The essential features of the self-motion were reproduced by a numerical calculation in relation to the spatial distribution of the camphor layer at the air−water interface.

We report the autonomous motion of a mercury drop in the concentration field of a dissolving oxidant crystal. A mercury drop and a K2Cr2O7 crystal were placed ∼10 mm apart in a Petri dish filled with 1 M HNO3 or H2SO4. When the front of the dissolving bichromate reached the edge of the circular Hg drop, the latter began to elongate and to move toward the crystal. This happened in the form of one (for H2SO4) or several (for HNO3) rapid “attacks”. By analogy with the beating mercury heart we conclude that the shape and motion of the Hg drop are related to the anisotropy of the interfacial tension.

The characteristic motion of a 1,10-phenanthroline grain on an FeSO4 aqueous phase was investigated as a simple example of an autonomous motor. The uniform motion of the grain changed to intermittent motion (periodic change between motion and rest) and its period and resting time increased depending on the concentration of FeSO4 (CFeSO4). However, this intermittent motion reverted to uniform motion and the velocity increased with a further increase in CFeSO4. The nature of this characteristic motion depending on CFeSO4 is discussed in relation to the surface tension, which depends on surface concentration of surface active layer composed of 1,10-phenanthroline and a tris(1,10-phenanthroline) complex as the driving force.

The self-motion of a solid scraping at an air/water interface was investigated. The self-motion of a camphoric acid scraping changed characteristically depending on the pH of the aqueous phase. With an acidic aqueous phase, the camphoric acid scraping maintains a fairly constant velocity. At neutral pH, intermittent motion was observed. These characteristic motions are discussed in relation to the surface free energy which results when the camphoric acid layer diffuses from the scraping. The nature of the diffusion of the camphoric acid layer at the water surface could be observed by adding CaSO4 powder. These results imply the realization of chemomechanical energy transduction under isothermal conditions.