  Electric voltage applied in electrowetting can induce speading, sliding and
even jumping of an individual droplet by changing the intrinsic balance of
three-phase interfacial tensions, which has been widely used for droplet
manipulating in microfluidics and lab-on-a-chip devices in over decades. In the
present paper, we present an analytical prediction of jumping velocity for
droplets electrowetting on textured hydrophobic surfaces with different wetting
states. In particular, we consider a liquid droplet wetting on a textured
hydrophobic substrate with a voltage applied between the droplet and the
substrate. Once the voltage is turned off, the energy stored in the droplet
during the electrowetting releases and could even result in the detachment of
the droplet. The effects of the initial and electro-wetting states, i.e.
Cassie-Baxter state and Wenzel state, on the jumping velocity of droplets are
systematically discussed. Based on energy conservation, the energy conversion
between the surface energy, internal viscous dissipation and the kinetic energy
of droplets in different wetting states are analysed. The close-form formulas
to predict the jumping velocity for different droplet wetting states are
systematically derived. Finally, the unified form for predicting the
electrowetting-induced jumping velocity of droplets on both flat and textured
substrates with different wetting states is obtained, which can describe the
jumping motion with various wetting conditions. This work provide theoretical
insights on accurate control of the electrowetting-induced jumping motion of
droplets on textured hydrophobic surfaces.
