Surface 2019, surface charge density
(SCD) gradient printing-driven
droplet transport, has attracted considerable attention as a novel
and effective approach, which adopts the water droplet impacting a
nonwetting surface to create a reprintable SCD gradient pathway conveniently
and realizes the high-velocity and long-distance transport of droplets.
In the present work, we further investigated the effects of electrothermal
behavior on SCD gradient printing on hydrophobic surfaces by considering
the droplet impact dynamics. After the electrothermal function was
activated, the wettability of the hydrophobic surface improved in
terms of the spreading factor history and the infiltration depth,
which increased the probability of solid/liquid contact electrification
to generate a more favorable SCD gradient. Since the hydrophobic surface
was negatively charged by droplet impact, polarized droplets rolled
forward along the preprinted SCD gradient pathway due to opposite
charge attraction. Based on these results, we designed a SCD gradient
printer with an electrothermal function for hydrophobic surfaces.
Subsequently, the kinematic parameters of rolling droplets on hydrophobic
surfaces were observed and quantified to evaluate the improvements
resulting from the electrothermal function.