Abstract
Droplet impacting on solid or liquid interfaces is a ubiquitous phenomenon in nature. Although complete rebound of droplets is widely observed on superhydrophobic surfaces, the bouncing of droplets on liquid is usually vulnerable due to easy collapse of entrapped air pocket underneath the impinging droplet. Here, we report a superhydrophobic-like bouncing regime on thin liquid film, characterized by the contact time, the spreading dynamics, and the restitution coefficient independent of underlying liquid film. Through experimental exploration and theoretical analysis, we demonstrate that the manifestation of such a superhydrophobic-like bouncing necessitates an intricate interplay between the Weber number, the thickness and viscosity of liquid film. Such insights allow us to tune the droplet behaviours in a well-controlled fashion. We anticipate that the combination of superhydrophobic-like bouncing with inherent advantages of emerging slippery liquid interfaces will find a wide range of applications.
Highlights
Droplet impacting on solid or liquid interfaces is a ubiquitous phenomenon in nature
It is generally accepted that the air layer entrapped between the impinging droplet and underlying liquid plays an important role in modulating the outcome of droplet impact[41,47,48], though it is susceptible to rupture at high-impacting velocity
De Ruiter et al.[52,53,54] reported that a liquid droplet even bounces off from the flat hydrophilic solid surface with the aid of thin air cushion, whose evolution during droplet impact was studied with the reflection interference contrast microscopy (RICM)
Summary
Droplet impacting on solid or liquid interfaces is a ubiquitous phenomenon in nature. Complete rebound of droplets is widely observed on superhydrophobic surfaces, the bouncing of droplets on liquid is usually vulnerable due to easy collapse of entrapped air pocket underneath the impinging droplet. Through experimental exploration and theoretical analysis, we demonstrate that the manifestation of such a superhydrophobiclike bouncing necessitates an intricate interplay between the Weber number, the thickness and viscosity of liquid film. Despite significant progress on the air layer entrapment dynamics, it remains elusive that how and to what extent the liquid substrate can modulate the bouncing behaviour of an impinging droplet. Since there is an air layer entrapped on the thin liquid film, we can treat the film as composite interfaces Such interfaces are in striking contrast to superhydrophobic solid surfaces. It is expected that the impact dynamics of droplet on liquid interfaces will be totally different from that on superhydrophobic surfaces
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