Abstract
Droplet bouncing on repellent solid surfaces (e.g., the lotus leaf effect) is a common phenomenon that has aroused interest in various fields. However, the scenario of a droplet bouncing off another droplet (either identical or distinct chemical composition) while moving on a solid material (i.e., ricocheting droplets, droplet billiards) is scarcely investigated, despite it having fundamental implications in applications including self‐cleaning, fluid transport, and heat and mass transfer. Here, the dynamics of bouncing collisions between liquid droplets are investigated using a friction‐free platform that ensures ultrahigh locomotion for a wide range of probing liquids. A general prediction on bouncing droplet–droplet contact time is elucidated and bouncing droplet–droplet collision is demonstrated to be an extreme case of droplet bouncing on surfaces. Moreover, the maximum deformation and contact time are highly dependent on the position where the collision occurs (i.e., head‐on or off‐center collisions), which can now be predicted using parameters (i.e., effective velocity, effective diameter) through the concept of an effective interaction region. The results have potential applications in fields ranging from microfluidics to repellent coatings.
Highlights
The capillary pressure of the super-repellent coating has been estimated to be about seven times greater than that of the wetting pressures, considering a water droplet is released at a height of 10 cm and impacts on the surface without wetting
We find that the trend in contact time of droplet–droplet bouncing is similar to that of single droplet bouncing on superrepellent surfaces, and that the contact time directly relates to the surface tension of the liquid (Figure S10 and Video S7, Supporting Information)
The maximum deformation of the drops and contact time between drops are highly dependent on the position where the collision occurs; both parameters decrease with increasing angle of incidence
Summary
The understanding of droplets bouncing on surfaces (i.e., solid or liquid) has implications for diverse fields and applications including self-assembly,[1,2,3] self-cleaning,[4] imaging,[5] anti-icing,[6] heat transfer,[7] fire extinguishing,[8] fluid transfer,[9,10] force measurements,[11] droplet logic,[12] microfluidics,[13] sensing,[14] electronics,[15] splash dynamics,[16] wrapping,[17] and coatings.[18]. We found that as the collision becomes more off-center, the maximum deformation and contact time decreases, but can be scaled to the oscillation period through the use of “effective parameters” that scale the velocity or radius (or both) in relation to the interacting region of each droplet. These results demonstrate the important role of super-repellent surfaces for studying bouncing dynamics of liquid droplets across a wide range of contact scenarios, and we anticipate that the present study will catalyze investigations into other interfacial repulsion and droplet bouncing phenomena, as well as the engineering of repellent surfaces that display superior liquid mobility
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
