Dynamic behaviors of water droplets on superhydrophobic polyester films and woven and knitted fabrics

In this study, the behaviors of water droplets on superhydrophobic polyester (PET) films as well as on woven and knitted fabrics with different surface microstructures were analyzed. The water droplet volume, height of release ( h), and surface inclination were modified to study the dynamic behavior of water droplets using a pressure balance and the Weber number ( We). The droplet volume did not affect the static contact angle. However, the shedding and sliding angles decreased with an increase in droplet volume. The water droplets rebounded on the surface of the superhydrophobic PET films with nano-roughness regardless of the surface inclination angle or h. However, the water droplets with h = 10 cm were pinned on the horizontal surfaces of the woven and knitted fabrics with micro-sized pores, where the dynamic pressure ( Pd) exceeded the capillary pressure. On an inclined surface, the water droplets rebounded on the surface of the woven fabric, owing to a decrease in Pd and an increase in the surface inclination angle. However, on the surface of the knitted fabric, pinning was observed even when the surface was tilted, regardless of the inclination angle. The sliding velocity of the droplets after rebound decreased in the following order: film, knitted fabric, woven fabric. With an increase in the inclination angle of the surface and the droplet volume, the sliding velocity increased, which was accompanied by a decrease in vertical impact velocity ( V) and an increase in the gravitational force. In terms of We, the droplets with a low We rebounded on all superhydrophobic surfaces, whereas the droplets with a high We were pinned on the surface of the woven and knitted fabrics.