Directional Droplet Coalescence-Induced Jumping Regulated by Laplace Pressure

Coalescence-induced droplet jumping, a spontaneous droplet
transport
phenomenon, holds significant potential in anti-icing, anti-fogging,
self-cleaning, and enhancing condensation heat transfer. However,
droplet jumping has a low energy efficiency and an uncontrolled jumping
orientation, severely restricting its practical use. We demonstrate
experimentally that a pillar superhydrophobic surface may achieve
dimensionless jumping velocity vj* = 0.72 and outstanding energy efficiency η = 56%. Compared to a flat superhydrophobic surface, the energy efficiency
is raised by about 860%. The improvement in jumping efficiency is
due to the pillar limitations and regularization of the internal droplet
flow by restricting droplet deformation. For the first time, we have
accomplished controlled droplet directional jumping within the 45–130°
range by adjusting the magnitude and direction of the Laplace pressure.
In addition, we thoroughly investigate how directional droplet jumping
is affected by pillar geometric dimensions, droplet radius, and droplet
size mismatch. This work introduces a new avenue for increasing the
jumping velocity while managing the direction, resulting in better
droplet jumping performance in applications.