Abstract
Water droplet impact on surfaces is a ubiquitous phenomenon in nature and industry, where the time of contact between droplet and surface influences the transfer of mass, momentum and energy. To manipulate and reduce the contact time of impacting droplets, previous publications report tailoring of surface microstructures that influence the droplet - surface interface. Here we show that surface elasticity also affects droplet impact, where a droplet impacting an elastic superhydrophobic surface can lead to a two-fold reduction in contact time compared to equivalent rigid surfaces. Using high speed imaging, we investigated the impact dynamics on elastic nanostructured superhydrophobic substrates having membrane and cantilever designs with stiffness 0.5–7630 N/m. Upon impact, the droplet excites the substrate to oscillate, while during liquid retraction, the substrate imparts vertical momentum back to the droplet with a springboard effect, causing early droplet lift-off with reduced contact time. Through detailed experimental and theoretical analysis, we show that this novel springboarding phenomenon is achieved for a specific range of Weber numbers (We >40) and droplet Froude numbers during spreading (Fr >1). The observation of the substrate elasticity-mediated droplet springboard effect provides new insight into droplet impact physics.
Highlights
Water droplet impact on surfaces is a ubiquitous phenomenon in nature and industry, where the time of contact between droplet and surface influences the transfer of mass, momentum and energy
Through detailed experimental and theoretical analysis, we show that this novel springboarding phenomenon is achieved for a specific range of Weber numbers (We >40) and droplet Froude numbers during spreading (Fr >1)
In contrast to previous studies, we show that droplet dynamics can be altered and contact times reduced by introducing a second energy storage mechanism during impact – elastic energy of the substrate – in addition to surface energy of the droplet
Summary
Water droplet impact on surfaces is a ubiquitous phenomenon in nature and industry, where the time of contact between droplet and surface influences the transfer of mass, momentum and energy. For high speed impacts (We >1 2), droplets lift off near their maximum spreading diameter in a pancake-like shape, reducing their contact time by a factor of 4. These previous approaches require fabrication of miniature features on the impacted surface, and that the impacting droplet is precisely aligned www.nature.com/scientificreports/. Taking inspiration from nature (leaves) and human technology (springboards), we study droplet impact dynamics on elastic superhydrophobic substrates as a passive mechanism for controlling and reducing contact time. Further experimental observation and theoretical analysis elucidates a surface mediated energy storage mechanism arising from the coupling of the substrate elastic response to impact, and the droplet internal flow dynamics. We present new fundamental knowledge of droplet impact physics and provide a starting point for more advanced approaches to enhance the performance of droplet-based applications by using substrate elasticity to achieve enhanced thermal, mass, or momentum transport
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