On the mechanism of droplet rolling and spinning in inclined hydrophobic plates in wedge with different wetting states

Bekir Sami Yilbas,Abba Abdulhamid Abubakar,Ahmet Sahin,Mubarak Yakubu,Hussain Al-Qahtani,Abdullah Al-Sharafi

doi:10.1038/s41598-021-94523-8

Bekir Sami Yilbas, Abba Abdulhamid Abubakar + Show 4 more

Open Access

https://doi.org/10.1038/s41598-021-94523-8

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Abstract

A water droplet rolling and spinning in an inclined hydrophobic wedge with different wetting states of wedge plates is examined pertinent to self-cleaning applications. The droplet motion in the hydrophobic wedge is simulated in 3D space incorporating the experimental data. A high-speed recording system is used to store the motion of droplets in 3D space and a tracker program is utilized to quantify the recorded data in terms of droplet translational, rotational, spinning, and slipping velocities. The predictions of flow velocity in the droplet fluid are compared with those of experimental results. The findings revealed that velocity predictions agree with those of the experimental results. Tangential momentum generated, via droplet adhesion along the three-phase contact line on the hydrophobic plate surfaces, creates the spinning motion on the rolling droplet in the wedge. The flow field generated in the droplet fluid is considerably influenced by the shear rate created at the interface between the droplet fluid and hydrophobic plate surfaces. Besides, droplet wobbling under the influence of gravity contributes to the flow inside the rolling and spinning droplet. The parallel-sided droplet path is resulted for droplet emerging from the wedge over the dusty surface.

Highlights

A water droplet rolling and spinning in an inclined hydrophobic wedge with different wetting states of wedge plates is examined pertinent to self-cleaning applications
The contact angle measured for the surface one is 160° ± 2° and hysteresis are of 5° ± 1° The contact angle of the second surface is 145° ± 2° and hysteresis is of 5° ± 1°
The ratio shows that the droplet spinning velocity is considerably smaller than the rolling speed. This demonstrates that the momentum created for the droplet rolling is considerably larger than that of the tangential momentum because of the droplet retention forces generated over the threephase contact length of the droplet on the hydrophobic wedge surfaces

Summary

Introduction

A water droplet rolling and spinning in an inclined hydrophobic wedge with different wetting states of wedge plates is examined pertinent to self-cleaning applications. In the first case (case (a) in Fig. 1e), the water droplet (20μL) is considered to roll down over 10° inclined wedged fixture, which is formed by two surfaces having same hydrophobic states, i.e. both surfaces have the contact angle of 150°.

Results

Conclusion