Ellipsoidal droplet formation on anisotropic superhydrophobic copper surface

• Published in: Surface topography metrology and properties 2019-07, Vol.7 (3), p.35001
• Main Authors: Taher, Md Abu, Prasad, Hitheswar, Navanith Krishnan, P K, Desai, Narayana Rao, Naraharisetty, Sri Ram G
• Format: Article
• Language: English
• Subjects: anisotropic contact angles; laser writing; superhydrophobicity; TCL theory; wetting
• ISSN: 2051-672X; 2051-672X
• DOI: 10.1088/2051-672X/ab2d80

Superhydrophobic copper surfaces with contact angle (CA) as high as 158° are fabricated using the one-step process of femtosecond fiber laser writing. Low spacing between the laser scanning lines was chosen purposefully to observe the anisotropic surface structures on the copper surfaces. This resulted in the formation of an ellipsoidal water droplet with anisotropic CAs, which are different along the major and minor axes. We quantified an experimentally measured parameter that correlates the droplet anisotropy and is related to the one-dimensional root mean square surface height deviation (1D RMS SHD). Theoretical CAs prediction based on triple contact line (TCL) theory on an ellipsoidal droplet volume is formulated and the calculations are in excellent agreement with experimentally observed anisotropic CAs. We presented an analytical expression for effective volume function relating the anisotropic contact angles, height, and the three semi-major axes of the ellipsoidal droplet. These functional values and observed contact angles are falling within the experimental errors of less than 5%. This work strengthens the validity of TCL theory. Our method of fabrication, high CAs results, correlation with 1D RMS SHD and theoretical prediction of elliptical CAs on an anisotropic surface will guide to design surfaces for many future applications.