Sessile droplets coalescing on superhydrophobic substrates spontaneously jump
from the surface. In this process, the excess surface energy available at the
initiation of coalescence overcomes the minimal surface adhesion and manifests
as sufficient kinetic energy to propel the droplets away from the substrate.
Here, we show that the coalescence induced droplet jumping velocity is
significantly curtailed if the superhydrophobic substrate is flexible in
nature. Through detailed experimental measurements and numerical simulations,
we demonstrate that the droplet jumping velocity and jumping height can be
reduced by as much as 40 % and 64%, respectively, by synergistically tuning the
substrate stiffness and substrate frequency. We show that this hitherto
unexplored aspect of droplet coalescence jumping can be gainfully exploited in
water harvesting from dew and fog harvesting. Additionally, through an exemplar
butterfly wing substrate, we demonstrate that this effect is likely to manifest
on many natural superhydrophobic substrates due to their inherent flexibility