Droplet sliding on a rotating surface mediated by an asymmetric gas layer

Droplet impact can be widely seen in many applications, such as aircraft anti-icing, spray coating, and inkjet printing. In these applications, droplets always impact moving surfaces. The impact of droplets on a rotating surface and the gas layer beneath the droplet has rarely been studied while previous research mainly focused on the droplet dynamics after it impacts a stationary surface. Droplets may slide on a rotating surface mediated by an asymmetric gas layer. In this study, we experimentally study the droplet sliding during the impact of droplets on a rotating liquid film by using colored interferometry and high-speed imaging. Results show that an asymmetric micrometer-sized gas layer beneath the droplet can significantly prevent it from wetting the rotating liquid film. The peak of the gas layer profile moves along the rotating direction of the liquid film as the droplet slides. As the rotational angular velocity increases, the movement distance of the peak of the gas layer profile increases, and the droplet slides faster. The contact time of the droplet is almost constant when the rotational angular velocity of the liquid film ranges from 0 to 50 degrees/s. The dimensionless acceleration of the droplet during sliding is controlled by both the Bond and Capillary numbers a/g similar to Bo(1/2)Ca(1/3). In addition, as the Ohnesorge number increases, the maximum diameter of the gas layer during the droplet spreading decreases. A larger liquid viscosity can restrain the droplet bounce during the sliding of the droplet.