Wetting Effect on Patterned Substrates

• Published in: Advanced materials (Weinheim) Vol. 35; no. 25; pp. e2210745 - n/a
• Main Authors: Wang, Fei, Wu, Yanchen, Nestler, Britta
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.06.2023
• Subjects: anisotropic wetting morphology; Contact angle; Droplets; Heterogeneity; Hydrophobicity; Materials science; Morphology; patterned substrates; Substrates; Wetting; anisotropic wetting morphology; patterned substrates; wetting
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202210745

A droplet deposited on a solid substrate leads to the wetting phenomenon. A natural observation is the lotus effect, known for its superhydrophobicity. This special feature is engendered by the structured microstructure of the lotus leaf, namely, surface heterogeneity, as explained by the quintessential Cassie–Wenzel theory (CWT). In this work, recent designs of functional substrates are overviewed based on the CWT via manipulating the contact area between the liquid and the solid substrate as well as the intrinsic Young's contact angle. Moreover, the limitation of the CWT is discussed. When the droplet size is comparable to the surface heterogeneity, anisotropic wetting morphology often appears, which is beyond the scope of the Cassie–Wenzel work. In this case, several recent studies addressing the anisotropic wetting effect on chemically and mechanically patterned substrates are elucidated. Surface designs for anisotropic wetting morphologies are summarized with respect to the shape and the arrangement of the surface heterogeneity, the droplet volume, the deposition position of the droplet, as well as the mean curvature of the surface heterogeneity. A thermodynamic interpretation for the wetting effect and the corresponding open questions are presented at the end. Droplet wetting on patterned substrate is addressed by the Cassie–Wenzel theory (CWT). This review discusses recent applications of CWT and its limitations. Anisotropic wetting effects beyond the scope of CWT are summarized for droplet size comparable to the pattern dimension. An additional focus is placed on the case when droplet partially wets the pore for mechanically patterned substrate.