Abstract
The wetting property between liquid and solid is very important in many industries besides natural systems. The simplest method to determine the wetting property is just dropping a liquid drop on a solid surface and measuring a contact angle from the shape of the drop. Since the Young’s equation has been used as a basic equation to relate a contact angle and interfacial tensions over 200 years, it is important to understand a derivation and limits of the Young’s equation. We derived the Young’s equation following energy minimization with simple mathematics. By expanding the derivation, the modified forms of the Cassie-Baxter equation and the Wenzel equation were also derived. From analyses of the derivations, it was deduced that a contact angle on an ideal surface is only related to the infinitesimal region in the vicinity of contact line, not internal area surrounded by the contact line. Although the Cassie-Baxter model and the Wenzel model were not rigorously built, they have been widely used for a superhydrophobic surface, because the apparent forms are similar to those of rigorously derived models when the contact line can easily move on the surface.
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This paper is based on an invited lecture presented by the corresponding author at the 13th International Symposium on Applied Rheology (ISAR), held May 23, 2013, Seoul.
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Seo, K., Kim, M. & Kim, D.H. Validity of the equations for the contact angle on real surfaces. Korea-Aust. Rheol. J. 25, 175–180 (2013). https://doi.org/10.1007/s13367-013-0018-5
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DOI: https://doi.org/10.1007/s13367-013-0018-5