Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.colsurfa.2021.127197

Publishing type：Research paper (scientific journal)  

<title>Abstract</title>The horizontal spin of a ratchet motor by vertical vibration is reported. A macroscopic ratchet gear is placed on a granular bed, where nearly half of the gear is penetrated in the bed. The gear and granular bed are mechanically vibrated. The gear shows a random motion or one-way spin that depend on the diameter of the granules, vibration frequency, and degree of vertical motion allowed for the gear. Even when one-way spin is observed, the spin direction depends on the abovementioned factors. Although the dependency is complicated, it is deterministic because the motion or flows of granular matter determines it. The characteristics observed in the experiments are explained by a simple model that accounts for the statistical variance in the motion of the granular matter. Extraction of systematic motion from small and non-useful motions such as mechanical agitation will be developed into energy harvest technology and may facilitate the science of a spontaneously moving system in a uniform potential field.

DOI： 10.1038/s41598-021-91319-8

Other URL： http://www.nature.com/articles/s41598-021-91319-8

Publishing type：Research paper (scientific journal)  

DOI： 10.1252/kakoronbunshu.47.69

Publishing type：Research paper (scientific journal)  

© 2020 Author(s). The synchronization of chemically driven oscillators plays a crucial role in various biological motions. An artificial model system of these chemo-mechanical oscillators is proposed in this study. The oscillator is composed of three liquid layers (oil/water/oil), which exhibit a back and forth motion in a glass tube. This motion is caused by the chemical reaction between a water-soluble surfactant and oil-soluble anions. The frequency is unique for an individual experimental setup because it depends on the surface state of the glass sensitively. When the glass tube with the liquid oscillator is placed on a plate with mechanical vibration, the frequencies of the oscillator and mechanical vibration become similar within a certain frequency range of mechanical vibration. When two or more glass tubes are placed in a boat floating on a water surface, all frequencies agree with each other by the joggling motion of the boat. The entrainment into the external vibration and mutual synchronization on the boat are explained by a simple mathematical model. The proposed chemo-mechanical oscillator may be used as a primitive model system for studying the interplay of macroscopic motion and molecular scale processes that control chemically driven motion.

DOI： 10.1063/5.0006387

Authorship：Lead author   Publishing type：Research paper (scientific journal)  

© 2020 The Chemical Society of Japan. Biological functions are maintained by various types of molecular motors driven at several pico-newtons, where the driving force is obtained from a chemical potential difference within the microscale. Here, we show in detail artificial vesicles that generate mechanical work from a local pH gradient. This study demonstrates that they can be regarded as a molecular assembly machine. We have previously reported that the vesicles are composed of oleate and oleic acid and exhibit rhythmic shape changes. This cyclic motion involves both rotation of the entire vesicle and its inside-out inversion, which constitute relaxation and excitation processes, respectively, that sustain the cycle. These motions were observed under a quasi-steady state pH gradient, and the driving force of rotation was determined to be of the order of 10-210-1 pN, which is consistent with the membrane elasticity driving the deformation (vesicle inversion).

DOI： 10.1246/bcsj.20190348

Publishing type：Research paper (scientific journal)  

© 2020 Society of Powder Technology. All rights reserved. Belousov-Zhabotinsky (BZ) reaction is a typical example of chemical oscillation. For an application of BZ reaction to engineering, the downsizing of reaction field will be needed. We focus on liquid marble (LM) to solve this subject. LM is a stable sphere liquid covered with hydrophobic microparticles. We observed BZ reaction in LM to investigate the reaction property in small space. We succeeded in observing chemical oscillation for a long time in LM. During the observation, no bubble was produced although carbon dioxide is contained as reaction products. We found that LM tends to exhibit regular oscillation mode with a decrease in droplet size. In addition, the period of BZ reaction changes with the size. This can be explained from the effect of oxygen and the amount of particles covering a droplet. As a result, the oscillation period can be controlled by the droplet size and the amount of particles.

DOI： 10.4164/sptj.57.74

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Herein, the oscillation of an oil droplet on the surface of water is studied. The droplet contains an anionic surfactant that can react with the cations present in water. The oscillation starts after a random motion, and the oscillation pattern apparently depends on the cation species in the water phase. However, a common pattern is included. The cation species only affects the amplitude and frequency and sometimes perturbs the regular pattern owing to the instability at the oil/water interface. This common pattern is explained by a simple model that incorporates the surfactant transport from the droplet to the surrounding water surface. The dependency of the amplitude and frequency on cation species is expressed quantitatively by a single parameter, the product of the amplitude and square of frequency. This parameter depends on the cationic species and can be understood in terms of the spreading coefficient. The simple model successfully explains this dependency.

DOI： 10.3389/fchem.2019.00788

PubMed

Publishing type：Research paper (scientific journal)  

© 2019 American Chemical Society. A sustainable droplet motion that is driven by pH oscillation was obtained. The pH oscillation is only of a single pulse in a batch reactor. However, it shows continuous oscillation around the moving droplet, as the motion itself controls the diffusion flux in an asymmetric manner. Various types of motions that are spontaneous in nature may be obtained by a single-pulse oscillation coupled with mass transport.

DOI： 10.1021/acs.langmuir.9b02072

PubMed

Publishing type：Research paper (scientific journal)  

© 2019 Society of Powder Technology. All rights reserved. Liesegang phenomenon has been extensively studied experimentally and theoretically in the field of nonlinear science. However, there are few studies for its applications due to the high nonlinearity. The particles produced with the Liesegang phenomenon have been limited to microparticles of sparingly soluble salt for many years. In this study, in anticipation of more engineering application of this phenomenon, gold nanoparticles are synthesized by diffusing gold ions into a gel containing a reductant. At that time, we investigate the influence of diffusion conditions on particle formation. As a result, we found that the size of resultant particles depends on the gel position. Furthermore, we construct mathematical model expressing ion diffusion and particle growth based on Ostwald ripening to discuss the particle formation mechanism.

DOI： 10.4164/sptj.56.187

Kind of work：Joint Work  

Kind of work：Joint Work  

Kind of work：Single Work  

Kind of work：Joint Work  

Kind of work：Joint Work  

Kind of work：Joint Work  

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (general)