Effect of surface roughness on the angular acceleration for a droplet on a super-hydrophobic surface
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ISSN 2223-7690 CN 10-1237/TH
RESEARCH ARTICLE
Effect of surface roughness on the angular acceleration for a droplet on a super-hydrophobic surface Longyang LI1, Jingfang ZHU2, Zhixiang ZENG1,*, Eryong LIU3, Qunji XUE1 1
Key Laboratory of Marine Materials and Related Technologies, Zhejiang Key Laboratory of Marine Materials and Protective Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China
2
SEU-FEI Nano-Pico Center, Key Laboratory of MEMS of Ministry of Education, Southeast University, Nanjing 210096, China
3
School of Materials Science and Engineering, Xi'an University of Science and Technology, Xi'an 710054, China
Received: 01 November 2019 / Revised: 04 March 2020 / Accepted: 27 March 2020
© The author(s) 2020. Abstract: The motion of droplets on a super-hydrophobic surface, whether by sliding or rolling, is a hot research topic. It affects the performance of super-hydrophobic materials in many industrial applications. In this study, a super-hydrophobic surface with a varied roughness is prepared by chemical-etching. The adhesive force of the advancing and receding contact angles for a droplet on a super-hydrophobic surface is characterized. The adhesive force increases with a decreased contact angle, and the minimum value is 0.0169 mN when the contact angle is 151.47°. At the same time, the motion of a droplet on the superhydrophobic surface is investigated by using a high-speed camera and fluid software. The results show that the droplet rolls instead of sliding and the angular acceleration increases with an increased contact angle. The maximum value of the angular acceleration is 1,203.19 rad/s2 and this occurs when the contact angle is 151.47°. The relationship between the etching time, roughness, angular acceleration, and the adhesion force of the forward and backward contact angle are discussed. Keywords: super-hydrophobic surface; adhesive force; rolling friction; contact angle
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Introduction
In the industrial field, there are several great potential applications of super-hydrophobic surfaces. Some examples include drag reduction [1, 2], lubrication [3], anticorrosion [4–6], self-cleaning [7, 8], and antiicing [9]. As a result, the design, preparation, application, and theoretical model of super-hydrophobic systems have investigated [8, 10, 11]. There are many techniques that can fabricate super-hydrophobic surfaces, which include sol-gel [12–14], chemical-etching [15–17], chemical vapor deposition (CVD) [18], anodicoxidation [19, 20], and vapor-deposition [21, 22]. Super-hydrophobic surfaces are commonly defined by having a contact angle greater than 150° and
the rolling angle is less than 10° when the droplet contacts the solid surface. Although many factors influence super-hydrophobicity, surface roughness and surface energy are the dominant factors. To improve the hydrophobicity, it is necessary to provide an appropriate surface roughness for the materials with a low surface energy. There are many movement models of dro
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