Dynamic Characteristic of Droplet Collision at Hydrophilic-hydrophobic Interface

Droplet collision with different wettability surfaces will exhibit different dynamic behaviors. To study the dynamic behavior of droplets collision at the hydrophilichydrophobic interface, a superhydrophilic-superhydrophobic hybrid wettability surface was prepared. The droplets (the initial diameter D₀ is 1.80 mm) were controlled to collide on the superhydrophilic-superhydrophobic interface at different speeds. The results show that when the droplets collide with the hydrophilichydrophobic interface, the adjacent two extreme wettability surfaces will generate the driving force for droplet spreading. And the droplets will spread completely in the superhydrophilic region. The maximum spreading diameter can reach 5.51 mm and the droplet spreading coefficient β can be up to 2.93. When the droplet collides with the hydrophilic-hydrophobic interface at a certain speed, the droplet spreading and the droplet bounce occur simultaneously. The droplet spreading coefficient first increases, then decreases, and there is a “spike” in the spreading coefficient curve. The final spreading coefficient gradually increases and tends to be stable. The greater the impact speed, the larger the spreading coefficient in the early stage of spreading. The energy analysis during the droplet spreading process shows that the mutual conversion of droplet kinetic energy and surface energy is the key to droplet motion and spreading.