Investigation of the dew condensation and subsequent spontaneous jumping of droplets on the highly hydrophobic surface under cooling

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Superhydrophobic coatings with nano-scale random roughness structure were prepared using boehmite and hydrophobic silanes. The samples were cooled by Peltier cooling element, and spontaneous jumping of water droplets formed on the coatings by dew condensation was observed from two different directions using high-speed camera systems. Spontaneous jumping of water droplets occurred subsequent to coalescence of more than two water droplets, deformation, and shape recovery. Small jumping droplets exhibited great initial jumping velocity. Initial jumping velocity decreased with increasing the difference in droplet sizes before coalescence. Actual jumping velocity was smaller than the theoretical value. When the sample was declined at 30 degrees, jumping frequency of water droplets repeated the increasing-decreasing cycle against cooling time and sustained droplet removal property. The jumping height of water droplets was remarkably increased under an external electric field.