Bouncing, chasing, or pausing: Asymmetric collisions of active droplets

Chemically active droplets exhibit complex avoiding trajectories. While heterogeneity is inevitable in active matter experiments, it is mostly overlooked in their modeling. Exploiting its geometric simplicity, we fully resolve the head-on collision of two swimming droplets of different radii and demonstrate that even a small contrast in size critically conditions their collision and subsequent dynamics. We identify three fundamentally different regimes. The resulting high sensitivity of pairwise collisions is expected to profoundly affect their collective dynamics.