Jumping force of coalescing droplets on a superhydrophobic surface

We report a method to directly measure the jumping force during the coalescence of two water droplets on a superhydrophobic surface using a MEMS-based force sensor as shown in Figure 1(a). The sensor is designed to measure the jumping force during the coalescence of two droplets whose radii are several hundred μm. The measurement results show that the maximum jumping force could be more than 10 times larger than the total weight of the merged droplet. Moreover, the impulse calculated from the measured force was on the same order with the jumping momentum of the droplet. Therefore, our sensor is a useful tool to investigate the mechanism of coalescence-induced droplet jumping.