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We studied the self-propulsion of a camphor disk floating on a water surface using two types of ionic liquids (hexylammonium-trifluoroacetate (HHexam-TFA) and hexylethylenediaminium-trifluoroacetate (HHexen-TFA)). Bifurcation between continuous, oscillatory, and no motion was observed depending on the concentration of the ionic liquid. The bifurcation concentration between oscillatory and no motion for HHexam-TFA was lower than that for HHexen-TFA. The different bifurcation concentrations are discussed in relation to the surface tension and Fourier transform infrared spectra of the mixtures of camphor and ionic liquids. These results suggest that the interaction between the ionic liquid molecules at the air/water interface is weakened by the addition of camphor molecules and the features of self-propulsion vary due to the change in the driving force. [ABSTRACT FROM AUTHOR]

Autocatalysis induces nonlinearity in chemical and/or biological systems, and is important for understanding the emergence of life in nature. To enhance the autonomy of self‐propulsion in an open system, we introduced a Briggs–Rauscher (BR) reaction into self‐propelled droplet systems. In this study, a droplet composed of a BR solution in an oil phase containing a monoolein surfactant exhibited various types of motion, that is, continuous, oscillatory, and no motions of the droplet. The motions observed depended on the concentrations of potassium iodate and hydrogen peroxide in the BR solution. These results indicated that the driving force in this system was generated by the reaction between monoolein and one of the intermediates of the BR reaction, iodine. Our system can contribute to the establishment of a novel biomimetic object in which the autocatalytic process acts as a key factor for inducing various types of motion. [ABSTRACT FROM AUTHOR]

We investigated oscillatory motion of a camphor disk floating on water containing 5 mM hexylethylenediaminium trifluoroacetate (HHexen-TFA) as an ionic liquid (IL). The frequency of the oscillatory motion increased with increasing concentrations of the transition metal ions Cu 2+ and Ni 2+ but was insensitive to Na + , Ca 2+ , and Mg 2+ , the typical metal ions in the water phase. The surface tension of the water phase containing 5 mM HHexen-TFA also increased with increasing concentrations of Cu 2+ and Ni 2+ but was insensitive to Na + , Ca 2+ , and Mg 2+ . Based on density functional theory, metal-ion species-dependent frequency response is discussed with regard to surface tension as the force of self-propulsion and complex formation between HHexen-TFA and metal ions. These results suggest that complex formation between the transition metal ions (Cu 2+ , Ni 2+ ) and the ethylenediamine group in the IL increases the surface tension around the camphor disk, resulting in an increase in the frequency of oscillatory motion with increasing concentrations of Cu 2+ or Ni 2+ . The present study suggests that the nature of self-propulsion can be created by complexation, which changes the force of self-propulsion.