Asymmetric deposition on high-speed moving superhydrophobic surfaces†

Droplet deposition on high-speed moving superhydrophobic (HM-SHB) surfaces is important for industrial and agricultural purposes. However, current deposition additives for static SHB surfaces don't work well on HM-SHB surfaces. This is because the highly asymmetric balloon-string impact dynamics and the prompt air entrainment reduce the contact time for aqueous droplets by more than 63%, causing the deposition process to become more difficult. To solve this problem, the asymmetry between the upstream and downstream parts has been reduced to a spindle deposition shape. This was performed by adding a large quantity of synthetic polymer and small amounts of surfactant to increase viscosity and decrease surface tension, thereby reducing relative lateral solid–liquid velocity and consequently inhibiting air entrainment. Additionally, the relationship between the dynamic capillary number and dynamic contact angle is disclosed to be linear, taking into account viscosity, surface tension, and solid–liquid relative motion speed. The novel strategy results in a hundredfold increase in deposition coverage when imitating drone spraying. This work improves our understanding of the complicated impact dynamics on HM-SHB surfaces, enhances liquid deposition, and offers solutions for related applications.