Large-Area Fabrication of Droplet Pancake Bouncing Surface and Control of Bouncing State

Abstract

Superhydrophobic pillar arrays, which can generate the droplet pancake bouncing phenomenon with reduced liquid-solid contact time, have huge application prospects in anti-icing of aircraft wings from freezing rain. However, the previously reported pillar arrays, suitable for obtaining pancake bouncing, have a diameter ≤100 μm and height-diameter ratio >10, which are difficult to fabricate over a large area. Here, we have systematically studied the influence of the dimension of the superhydrophobic pillar arrays on the bouncing dynamics of water droplets. We show that the typical pancake bouncing with 57.8% reduction in contact time with the surface was observed on the superhydrophobic pillar arrays with 1.05 mm diameter, 0.8 mm height, and 0.25 mm space. Such pillar arrays with millimeter diameter and <1 height-diameter ratio can be easily fabricated over large areas. Further, a simple replication-spraying method was developed for the large-area fabrication of the superhydrophobic pillar arrays to induce pancake bouncing. No sacrificial layer was needed to reduce the adhesion in the replication processes. Since the bouncing dynamics were rather sensitive to the space between the pillars, a method to control the contact time, bouncing shape, horizontal bouncing direction, and reversible switch between pancake bouncing and conventional bouncing was realized by adjusting the inclination angle of the shape memory polymer pillars.

Smart Wetting Control on Shape Memory Polymer Surfaces

“…Superhydrophobic surfaces with tunable microstructures can overcomet he shortcomings of surfaces with static microstructures, for which the bouncing propertyi sc onstanta nd uncontrollable, and thus, are more attractive for complex intelligent devices.Agood example of this research is reported by Songe tal. [32] As showni n Figure 8a,h ierarchically structuredp illars with ad iameter, height, and spacingo fa bout1 .05, 0.8, and 0.25 mm, respectively,w ere prepared on the same substrate as that used in our work. [13] The SMP pillarsw ere easily pressed aslant for differenti nclination angles( a)u nder heatingc onditions.…”

“…SEM images of SMP pillars with titling angles (a)o fabouta)90, b) 32, and c) 08.Inset:aschematic illustrationo fthe tilting pillars. d) Different bouncingp henomena for aw ater droplet on SMP pillars with different a. Reproduced with permission from ref [32]…”

Pillars of Life: Is There a Relationship between Lifestyle Factors and the Surface Characteristics of Dragonfly Wings?

“…Droplet contact times were approximately threefold longer than the calculated theoretical time and significantly higher than synthetic surfaces that exhibit similar pancake bouncing behavior. 37 , 38 This extended droplet contact time is likely a function of the dynamic nature of the dragonfly wing surface which displays bending upon droplet impact. Dragonfly wings are flexible and are able to rapidly deform, allowing them to withstand stresses associated with flight.…”

“…Comparatively, synthetic surfaces examined in previous droplet bouncing studies are typically flat or uniformly angled with limited or no flexibility in the macrostructure. 37 , 38 , 40 , 44 , 45 While we focused on the wing surface nanoarchitecture in this study, it is likely that interactions of macroscale features such as membrane corrugations, veins, and microtrichia contribute to the behavior of impacting water droplets. These findings warrant further work to understand more about this complex natural system.…”

Computational Intelligence‐Assisted Understanding of Nature‐Inspired Superhydrophobic Behavior

“…On such surfaces water droplets are able to bounce, and the contact time between bouncing water droplets and superhydrophobic surfaces becomes a key factor of their dynamic characterization 7. The water bouncing motion is well studied by physicists and the contact time can be further reduced by tuning the surface micromorphology and droplet Weber number to achieve “nonaxisymmetric bouncing,”8 “pancake bouncing,”9 and “sausage bouncing”10 of water droplets.…”