title: Superhydrophobicity on two-tier rough surfaces fabricated by controlled growth of aligned carbon nanotube arrays coated with fluorocarbon.
abstract: Considerable effort has been expended on theoretical studies of superhydrophobic surfaces with two-tier (micro and nano) roughness, but experimental studies are few due to the difficulties in fabricating such surfaces in a controllable way. The objective of this work is to experimentally study the wetting and hydrophobicity of water droplets on two-tier rough surfaces for comparison with theoretical analyses. To compare wetting on micropatterned silicon surfaces with wetting on nanoscale roughness surfaces, two model systems are fabricated: carbon nanotube arrays on silicon wafers and carbon nanotube arrays on carbon nanotube films. All surfaces are coated with 20 nm thick fluorocarbon films to obtain low surface energies. The results show that the microstructural characteristics must be optimized to achieve stable superhydrophobicity on microscale rough surfaces. However, the presence of nanoscale roughness allows a much broader range of surface design criteria, decreases the contact angle hysteresis to less than 1 degrees , and establishes stable and robust superhydrophobicity, although nanoscale roughness could not increase the apparent contact angle significantly if the microscale roughness dominates.
authors.affiliation: School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
authors.forename: Lingbo
authors.initials: L
authors.lastname: Zhu
authors.forename: Yonghao
authors.initials: Y
authors.lastname: Xiu
authors.forename: Jianwen
authors.initials: J
authors.lastname: Xu
authors.forename: Prabhakar A
authors.initials: PA
authors.lastname: Tamirisa
authors.forename: Dennis W
authors.initials: DW
authors.lastname: Hess
authors.forename: Ching-Ping
authors.initials: CP
authors.lastname: Wong
mesh_terms: D005466:Fluorocarbons / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D037742:Nanotubes, Carbon / Q000737:chemistry*; D012825:Silicon; D013499:Surface Properties; D017155:Wettability
chemical_list: D005466:Fluorocarbons; D037742:Nanotubes, Carbon; D012825:Silicon