Excitability induced binary interactions in self-propelled Belousov-Zhabotinsky droplets

The Belousov-Zhabotinsky (BZ) reaction is an example of a nonlinear chemical oscillator, where the reagents undergo successive oxidation and reduction over a period of time. When a droplet containing the BZ reaction is placed in an oily medium, it can move without external force. This self-propelled motion of the BZ droplet is caused by the chemical oscillation inside the BZ droplet and the Marangoni effect at its boundary. In this experimental work, we explore the interaction of the BZ droplet as a function of excitability (sodium bromate). We find that the frequency of oscillations, the speed of the BZ droplet, and changes in the direction of motion increase as a function of sodium bromate. When there are multiple droplets, the interaction time between droplets decreases with sodium bromate. We also analysed the interaction of the two droplets when their volumes are different. We observed three types of interactions: the droplets can approach head-on, they move along parallel paths, or the big droplet follows the smaller droplet. The interaction time is maximum when the big droplet follows the small droplet. These findings offer insights into controlling and understanding emergent phenomena in active matter systems.