Oscillation of Speed of a Self-Propelled Belousov-Zhabotinsky Droplet

Self-propelled objects can become potential biomimetic micromachines, but a versatile strategy is required to add the desired functions. Introducing a characteristic chemical reaction is a simple answer; however, the problem is how the chemical reaction is coupled to the self-propelled motion. We propose a strategy to select the chemical reaction so that its product or intermediate affects the driving force of a self-propelled object. To demonstrate this strategy, we put an aqueous droplet of nonlinear chemical reaction, the Belousov-Zhabotinsky (BZ) reaction, into an oil phase including a surfactant, where an aqueous droplet was driven by an interfacial reaction of the surfactant and bromine. The results exhibited oscillation of speed, and it was synchronized with the redox oscillation of the BZ reaction in the droplet. Bromine is one of the intermediates of the BZ reaction, and thus the droplet motion well-reflected the characteristics of the BZ reaction.