The Role of Electric Pressure/Stress Suppressing Pinhole Defect on Coalescence Dynamics of Electrified Droplet

Jaehyun Lee,Sunghwan Jung,Jihoon Kim,Doyoung Byun,Ehsan Esmaili,Hyunggun Kim,Hosung Kang,Giho Kang,Baekhoon Seong

doi:10.3390/coatings11050503

Jaehyun Lee, Sunghwan Jung + Show 7 more

Open Access

https://doi.org/10.3390/coatings11050503

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Abstract

The dimple occurs by sudden pressure inversion at the droplet’s bottom interface when a droplet collides with the same liquid-phase or different solid-phase. The air film entrapped inside the dimple is a critical factor affecting the sequential dynamics after coalescence and causing defects like the pinhole. Meanwhile, in the coalescence dynamics of an electrified droplet, the droplet’s bottom interfaces change to a conical shape, and droplet contact the substrate directly without dimple formation. In this work, the mechanism for the dimple’s suppression (interfacial change to conical shape) was studied investigating the effect of electric pressure. The electric stress acting on a droplet interface shows the nonlinear electric pressure adding to the uniform droplet pressure. This electric stress locally deforms the droplet’s bottom interface to a conical shape and consequentially enables it to overcome the air pressure beneath the droplet. The electric pressure, calculated from numerical tracking for interface and electrostatic simulation, was at least 108 times bigger than the air pressure at the center of the coalescence. This work helps toward understanding the effect of electric stress on droplet coalescence and in the optimization of conditions in solution-based techniques like printing and coating.

Highlights

The coalescence of a droplet is one of the fundamental fluid dynamic phenomena that commonly occur in nature [1,2,3]
In surfaces and elucidated the suppression mechanism for dimple formation based on electric surfaces and elucidated the suppression mechanism for dimple formation based on elecpressure (Pelectric ) and electric Weber number (Weelec )
When the electrically neutral collides on the dry surface, the droplet interface of the bottom apex is distorted owing droplet collides on the dry surface, the droplet interface of the bottom apex is distorted to the local pressure inversion, and the dimple with air entrapment occurs

Summary

Introduction

The coalescence of a droplet is one of the fundamental fluid dynamic phenomena that commonly occur in nature [1,2,3]. The additional external conditions (multi-physics such as thermodynamics or electromagnetics) can affect the coalescence behaviors and sometimes create unexpected phenomena. For this reason, many studies on droplet coalescence under a multi-physics condition have been reported diversely until nowadays. Even though droplet coalescence is universally observable and has been researched for a long time, we cannot stop emphasizing the importance of continuous studies on novel droplet coalescence

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