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Multiphase Science and Technology
SJR: 0.183 SNIP: 0.483 CiteScore™: 0.5

ISSN Печать: 0276-1459
ISSN Онлайн: 1943-6181

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Multiphase Science and Technology

DOI: 10.1615/MultScienTechn.v27.i2-4.40
pages 147-158

CONTACT ANGLE VARIATION IN WATER DROPLETS ON LOW-SURFACE-ENERGY SOLIDS

Yukihiro Yonemoto
Priority Organization for Innovation and Excellence, Kumamoto University, 2-39-1 Kurokami, Chuo, Kumamoto 860-8555, Japan
Tomoaki Kunugi
Department of Nuclear Engineering, Kyoto University, Kyoto Daigaku-Katsura, Nishikyo-ku, Kyoto, Japan

Краткое описание

After deposition on solid surfaces, evaporating droplets affect the cooling of heat sources, ink-jet printing, and painting. During evaporation, the behavior of interfaces is very important because heat transfers occur through interfaces. As a droplet on a surface decreases its volume, its contact angle is not constant; a variation is generally observed, implying that the Young equation cannot explain this phenomenon. Moreover, the contact line recedes as the contact angle changes. This is referred to as the size dependence of the contact angle. This behavior is mainly explained based on the concept of line tension. From long-established research, line tension was found to depend on the contact line radius and contact angle, and takes negative, positive, or zero values. However, their relationship remains an unexplained problem to the present day. In this study, water droplet behavior under natural evaporation is experimentally observed and analyzed. The observed behavior, specifically the size dependence of the contact angle, is modeled based not on the line tension concept but on the concept of work of adhesion and the free energy of the contact area. Our model shows good agreement with the experimental data in regard to the size dependence of the contact angle during natural evaporation of water droplets. In addition, the size and contact angle dependences of the line tension are elaborated based on our model.


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