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Study of the Classical Cassie Theory and Wenzel Theory Used in Nanoscale

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Abstract

Recently, there are hesitations in the application scope of the classical Cassie theory and Wenzel theory. In this paper, Molecular Dynamics (MD) simulations are used to study these two theories used in the nanoscale and find their limitations. The effect of parameters including solid fractions (or roughness factors), arrangement of pillars (with same solid fractions), pillar height, and droplet size on contact angles was investigated. It shows that the Cassie equation is suitable for droplets on uniform pillared surfaces including different solid fractions, arrangement of pillars and pillar height, when there is no meniscus of droplets. The Wenzel equation is also suitable for droplets on uniform pillared surfaces including different roughness factors, arrangement of pillars and pillar heights. Moreover, whether the droplet size has an influence on the contact angle depends on the pinned place of the contact line. In the Wenzel state, the contact line is pinned although increasing the droplet size, resulting in increasing the contact angle, while the contact angle decreases to the initial value again when the droplet size increases enough to allow the contact line moving to the next pillar. The results provide insights toward the wettability of droplets on surfaces in nanoscale.

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Acknowledgment

This work was supported by the National Natural Science Foundation of China (51905315), Shandong Provincial Natural Science Foundation (ZR2019 BEM012), the Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents (2019RCJJ001), the Fundamental Research Funds for the Central Universities (20CX02317A), the Opening Fund of National Engineering Laboratory of Offshore Geophysical and Exploration Equipment, and the Project of Shandong Province Higher Educational Young Innovative Talent Introduction and Cultivation Team (Environment function material innovation team).

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Authors and Affiliations

  1. School of Material Science and Engineering, Shandong University of Science and Technology, Qingdao, 266590, China

    Hao Li & Xiaolei Feng

  2. College of Pipeline and Civil Engineering, China University of Petroleum (East China), Qingdao, 266580, China

    Kai Zhang

  3. National Engineering Laboratory of Offshore Geophysical and Exploration Equipment, China University of Petroleum, Shandong, 266580, China

    Hao Li

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  1. Hao Li
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  2. Xiaolei Feng
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  3. Kai Zhang
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Correspondence to Kai Zhang.

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Li, H., Feng, X. & Zhang, K. Study of the Classical Cassie Theory and Wenzel Theory Used in Nanoscale. J Bionic Eng 18, 398–408 (2021). https://doi.org/10.1007/s42235-021-0029-8

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