title: Design and fabrication of a superhydrophobic glass surface with micro-network of nanopillars.
abstract: The wetting property of a superhydrophobic glass surface with a micro-network of nanopillars fabricated from colloidal lithography and plasma etching is investigated in this paper. The micro-network distribution of nanospheres can be modulated by diluting the nanosphere concentration and controlling the spin rate. The micro-network of nanospheres spun on the glass surface serves as a mask for nanopillars during the plasma etching process. After the fabrication, the nano-structured surface is treated with fluoroalkylsilane self-assembled monolayers to obtain superhydrophobicity. Among several spin rates, the minimum colloidal network area density from a 100 nm polystyrene nanosphere solution diluted to 0.026% was found at a spin rate of 4000 rpm. The sample with the lowest network area density shows a good quality of superhydrophobicity, having the highest water contact angle and the lowest sliding angle among samples with other network area densities. In particular, samples with a micro-network of pillars also showed mechanical robustness against finger rubbing. To assess the superhydrophobic behavior in-depth, a size-dependent contact angle equation is proposed for use with a high contact angle (>135°) and with a Bo (Bond number) ≪ 1. Furmidge's sliding angle equation is also modified; it is derived considering a static contact angle to simplify the prediction of the sliding angle. The contact and sliding angle measurements from samples with a micro-network of nanopillars show good agreement with the proposed equations.
authors.affiliation: Department of Nature-Inspired Nanoconvergence Systems, Korea Institute of Machinery and Materials, Yuseong-gu, Daejeon, Republic of Korea.
authors.forename: Joonsik
authors.initials: J
authors.lastname: Park
authors.forename: Hyuneui
authors.initials: H
authors.lastname: Lim
authors.forename: Wandoo
authors.initials: W
authors.lastname: Kim
authors.forename: Jong Soo
authors.initials: JS
authors.lastname: Ko