A superhydrophobic surface is a surface with a water contact angle close to or higher than 150°. In this feature article, we review the historical and present research on superhydrophobic surfaces, including the characterization of superhydrophobicity, different ways to fabricate rough surfaces, and low-surface-energy modifications on inorganic and organic rough surfaces. It is the combination of surface roughness and low-surface-energy modification that leads to superhydrophobicity. Notably, research on superhydrophobic surfaces has not only fundamental interest but various possible functional applications in micro- and nano-materials and devices.

Superhydrophobic surfaces: from structural control to functional application

Design, and Applications Shutao Wang,†,‡ Kesong Liu, Xi Yao, and Lei Jiang*,†,‡,§ †Laboratory of Bio-inspired Smart Interface Science, Technical Institute of Physics and Chemistry, and ‡Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry and Environment, BeiHang University, Beijing 100191, People’s Republic of China Department of Biomedical Sciences, City University of Hong Kong, Hong Kong P6903, People’s Republic of China

Bioinspired Surfaces with Superwettability: New Insight on Theory, Design, and Applications

Mimicking natural superhydrophobic surfaces and grasping the wetting process: A review on recent progress in preparing superhydrophobic surfaces

Super-Hydrophobic Surface of Aligned Polyacrylonitrile Nanofibers

We demonstrate a layer-by-layer processing scheme that can be utilized to create transparent superhydrophobic films from SiO2 nanoparticles of various sizes. By controlling the placement and level of aggregation of differently sized nanoparticles within the resultant multilayer thin film, it is possible to optimize the level of surface roughness to achieve superhydrophobic behavior with limited light scattering. Transparent superhydrophobic films were created by the sequential adsorption of silica nanoparticles and poly(allylamine hydrochloride). The final assembly was rendered superhydrophobic with silane treatment. Optical transmission levels above 90% throughout most of the visible region of the spectrum were realized in optimized coatings. Advancing water droplet contact angles as high as 160 degrees with low contact angle hysteresis (<10 degrees ) were obtained for the optimized multilayer thin films. Because of the low refractive index of the resultant porous multilayer films, they also exhibited antireflection properties.

Transparent superhydrophobic films based on silica nanoparticles

Transparent, superhydrophobic coating films have been prepared on polymer substrates at low temperatures through the sol-gel method. Al2O3 gel films were prepared on poly(ethylene terephthalate) substrates from Al(O-sec-C4H9)3 chemically modified with ethyl acetoacetate. A small roughness of about 20–50 nm was found to form on the surface of the Al2O3 gel films dried at room temperature and then immersed in hot water at 60°C. The electron diffraction measurements have shown that this roughened surface consists of pseudoboehmite nanocrystals. The coating of hydrolyzed fluoroalkyltrimethoxysilane on the Al2O3 gel films with the small roughness produced transparent, superhydrophobic films with contact angle for water larger than 150°.

Formation of Superhydrophobic Alumina Coating Films with High Transparency on Polymer Substrates by the Sol-Gel Method

Al2O3 gel films were prepared on poly(ethylene terephthalate) substrates from Al(O–sec-C4H9)3 chemically modified with ethyl acetoacetate A small roughness of about 20–50 nm was found to form on the Al2O3 gel films dried at room temperature and then immersed in hot water at 60 °C When hydrolyzed fluoroalkyltrimethoxysilane was coated on the Al2O3 films, transparent thin films with contact angle for water to be more than 150° were obtained

Kaori Kitamuro

Papers

Formation of Superhydrophobic Alumina Coating Films with High Transparency on Polymer Substrates by the Sol-Gel Method

Preparation of Super-Water-Repellent Alumina Coating Film with High Transparency on Poly(ethylene terephthalate) by the Sol–Gel Method