Geometrical and chemical sensing of an active droplet

A self-propelled droplet of 1-pentanol was found to sense its geometrical and chemical asymmetry in its environment. Experimentally, it is found that in its environment, the drop was able to sense geometrical asymmetry with 80% probability and chemical asymmetry with 100% probability. In our liquid-on-a-liquid system, the main reason behind this geometrical sensing is the unbalanced forces induced because of the geometrical imbalance in the environment while in chemical asymmetry, a fixed drop of 1 pentanol renders asymmetry in the concentration profile in the surroundings. For a better physical understanding of a drop in a Y-shaped channel, we developed a minimal numerical model considering suitable Marangoni forces caused by the surface tension gradient and Yukawa-type interaction. The numerical model and statistical analysis corroborated the experimental findings qualitatively as well as quantitatively.