Abstract

The motion of a water droplet in a hydrophobic wedge fixture was examined to assess droplet rolling and spinning for improved dust mitigation from surfaces. A wedge fixture composed of two inclined hydrophobic plates had different wetting states on surfaces. Droplet rolling and spinning velocities were analyzed and findings were compared with the experiments. A wedge fixture was designed and realized using a 3D printing facility and a high speed recording system was adopted to evaluate droplet motion in the wedge fixture. Polycarbonate sheets were used as plates in the fixture, and solution crystallization and functionalized silica particles coating were adopted separately on plate surfaces, which provided different wetting states on each plate surface while generating different droplet pinning forces on each hydrophobic plate surface. This arrangement also gave rise to the spinning of rolling droplets in the wedge fixture. Experiments were extended to include dust mitigation from inclined hydrophobic surfaces while incorporating spinning- and rolling droplet and rolling droplet-only cases. The findings revealed the wedge fixture arrangement resulted in spinning and rolling droplets and spinning velocity became almost 25% of the droplet rolling velocity, which agrees well with both predictions and experiments. Rolling and spinning droplet gave rise to parallel edges droplet paths on dusty hydrophobic surfaces while striations in droplet paths were observed for rolling droplet-only cases. Spinning and rolling droplets mitigated a relatively larger area of dust on inclined hydrophobic surfaces as compared to their counterparts corresponding to rolling droplet-only cases.

Highlights

  • The rate of dust storms around the globe is increasing because of climate change

  • Rolling and spinning liquid droplets on inclined wedge fixture (V-shape) consisting of hydrophobic surfaces with different wetting states were studied towards achieving improved droplet path geometry on dusty surfaces

  • This arrangement enabled the movement of a rolling and spinning droplet smoothly transiting onto the inclined flat hydrophobic surface

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Summary

Introduction

The rate of dust storms around the globe is increasing because of climate change. Devices in open environments are exposed to dusty weather conditions for long durations, which gradually degrade device performances. Increasing droplet pinning causes sliding and rolling of droplet motion on hydrophobic surfaces, which alters droplet dynamics and the amount of dust mitigation from surfaces. Roundness, and pore diameter, droplet motion changes from rolling to sliding This becomes critical as pore sites are partially filled with liquid such as water condensate in humid air ambient. The rolling mode of large size droplets (≥30 μL) suffers from large puddling, which gives rise to striation edge features in the droplet paths on dusty hydrophobic surfaces. This creates geometrically-irregular cleaned surfaces as compared to that created by small volume droplets [20]. Dust mitigation from inclined hydrophobic flat surfaces by a rolling-only droplet, and a rolling and spinning droplet was compared in the frame of self-cleaning applications

Experimental
Results and Discussion
Hydrophobizing of Wedge Surfaces and Dust Properties
Droplet Rolling and Spinning Dynamics
10. Predicted
Conclusions
R2 dvy m
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