Periodic Oscillatory Motion of a Self-Propelled Motor Driven by Decomposition of H O by Catalase.

A self-propelled motor driven by the enzymatic reaction of catalase adsorbed onto a filter paper floating on an aqueous solution of H O was used to study nonlinear behavior in the motor's motion. An increase in the concentration of H O resulted in a change from no motion to irregular oscillatory motion, periodic oscillatory motion, and continuous motion. The mechanisms underlying oscillation and mode bifurcation are discussed based on experimental results on O bubble formation and growth on the underside of the motor.

Tough Physical Double-Network Hydrogels Based on Amphiphilic Triblock Copolymers.

A series of physical double-network hydrogels is synthesized based on an amphiphilic triblock copolymer. The gel, which contains strong hydrophobic domains and sacrificial dynamic bonds of hydrogen bonds, is stiff and tough, and even stiffens in concentrated saline solution. Furthermore, due to its supramolecular structure, the gel features improved self-healing and self-recovery abilities.

Coupled instabilities of surface crease and bulk bending during fast free swelling of hydrogels.

Most studies on hydrogel swelling instability have been focused on a constrained boundary condition. In this paper, we studied the mechanical instability of a piece of disc-shaped hydrogel during free swelling. The fast swelling of the gel induces two swelling mismatches; a surface-inner layer mismatch and an annulus-disc mismatch, which lead to the formation of a surface crease pattern and a saddle-like bulk bending, respectively.

Bifurcation phenomena of two self-propelled camphor disks on an annular field depending on system length.

Mode selection and bifurcation of a synchronized motion involving two symmetric self-propelled objects in a periodic one-dimensional domain were investigated numerically and experimentally by using camphor disks placed on an annular water channel. Newton's equation of motion for each camphor disk, whose driving force was the difference in surface tension, and a reaction-diffusion equation for camphor molecules on water were used in the numerical calculations. Among various dynamical behaviors found numerically, four kinds of synchronized motions (reversal oscillation, stop-and-move rotation, equally spaced rotation, and clustered rotation) were also observed in experiments by changing the diameter of the water channel.

Chemical wave propagation preserved on an inhibitory field in the ruthenium-catalyzed Belousov-Zhabotinsky reaction.

The propagation of a chemical wave on an inhibitory field, which was wedged between two excitable fields, was investigated for the photosensitive Belousov-Zhabotinsky (BZ) reaction. With an increase in the width of the inhibitory field between the excitable fields (W), the chemical wave divided into two waves at W = Wα. The divided chemical waves then coalesced at W = Wβ with a decrease in W.

Collective motion of symmetric camphor papers in an annular water channel.

We investigate the collective motion of symmetric self-propelled objects that are driven by a difference in the surface tension. The objects move around an annular water channel spontaneously and interact through the camphor layer that develops on the water surface. We found that two collective motion modes, discrete and continuous density waves, are generated depending on the number of self-propelled objects.

Oscillation of a polymer gel entrained with a periodic force.

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.

Reciprocating motion of a self-propelled object on a molecular layer.

The mode change of a simple autonomous motor depending on the nature of a monolayer on water is investigated. A camphor disk is floated on a molecular layer of N-stearoyl-p-nitroaniline (C(18)ANA), which gives a surface-pressure (π)-area per molecule (A) isotherm with a local maximum and a local minimum. The nature of the camphor motion changes depending on A, and in particular, reciprocating motion is observed at a lower A while cutting out its own trajectory of motion.

Mode change in the self-motion of a benzoquinone disk coupled with a NADPH system.

The self-motion of a benzoquinone (BQ) disk on NADPH was investigated as the coupling of an autonomous motor and an enzyme reaction. In the absence of the enzyme reaction, features of motion changed depending on the concentration of NADPH, that is, continuous motion→ intermittent oscillatory motion→ no motion. When the reverse reaction from NADP(+) to NADPH was introduced into the system with the addition of an enzyme reaction, continuous motion changed to intermittent oscillatory motion with small amplitude.

Suppression and regeneration of camphor-driven Marangoni flow with the addition of sodium dodecyl sulfate.

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.

Oscillation and synchronization in the combustion of candles.

We investigate a simple experimental system using candles; stable combustion is seen when a single candle burns, while oscillatory combustion is seen when three candles burn together. If we consider a set of three candles as a component oscillator, two oscillators, that is, two sets of three candles, can couple with each other, resulting in both in-phase and antiphase synchronization depending on the distance between the two sets. The mathematical model indicates that the oscillatory combustion in a set of three candles is induced by a lack of oxygen around the burning point.