Fig. 2: CE between coalescence-induced jumping droplets and superhydrophobic surfaces.
a Molecular structure of FDT and DT, as well as the morphology of nano-structured copper oxide substrate with 12 minutes of etching. The scale bar is 5 μm. b The schematic of the setup that allows the observation of the contact electrification between superhydrophobic surfaces and coalescence-induced jumping droplets. The cooler aims to trigger the condensation of vapor and coalescence-induced jumping of condensate droplets by decreasing the temperature of superhydrophobic surfaces. Two electrodes build the directional electric field, allowing us to determine the charge polarity of jumping droplets by observing their motion trajectory. c On superhydrophobic FDT surfaces, jumping droplets experience a continuous ascent motion under the upward electric field, denoting the generation of positive charges in droplets during CE. d On superhydrophobic DT surfaces, jumping droplets acquire negative charges, leading to initial jumping and followed falling motion under the upward electric field. The contact angles of water droplets on FDT and DT surfaces are ∼ 156.2 o and ∼ 155.4o, respectively, shown in the insets.
