Static and dynamic hydrophobicity of alumina-based porous ceramics impregnated with fluorinated oil
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Munetoshi Sakai Kanagawa Academy of Science and Technology, Takatsu-ku, Kawasaki-shi, Kanagawa 213-0012, Japan
Toshihiro Isobe and Sachiko Matsushita Department of Metallurgy and Ceramic Science, Graduate School of Science and Engineering, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8552, Japan
Akira Nakajimaa) Department of Metallurgy and Ceramic Science, Graduate School of Science and Engineering, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8552, Japan; and Kanagawa Academy of Science and Technology, Takatsu-ku, Kawasaki-shi, Kanagawa 213-0012, Japan (Received 15 April 2014; accepted 23 June 2014)
Using phase separation, alumina-based porous ceramics with three-dimensional frameworks were prepared, with fine structural roughness created by subsequent hot-water treatment. The pore volume of the porous alumina and its specific surface area increased concomitantly with increasing hot-water treatment time. Porous alumina/fluorinated oil bulk composites were prepared by coating hydrophobic silane onto the porous ceramic surface and subsequently impregnating fluorinated oil. A wetting ridge formed at the bottom of the water droplets on the composites. Partial contact between the water and solid surface was inferred from a comparison of interface energies in the system. The composites provided a smaller sliding angle (SA) than that of the sample without impregnating fluorinated oil. The composite with fine roughness exhibited longer sustainability of a small SA than that without fine roughness. Particle image velocimetry revealed that the dominant sliding mode for water droplets on this composite was slipping. The droplets moved on the surface under an external electric field. Coulombic force contributes to this motion.
I. INTRODUCTION
Wetting of a solid surface has been the subject of research at the border separating physics and chemistry for many years. Wettability control of a solid against a liquid is widely investigated in industry because it can support various beneficial physical and chemical phenomena related to solids and liquids. Wettability is commonly compared by the contact angle (CA) (h), which is given by Young’s equation as cSG ¼ cSL þ cLG cos u
;
ð1Þ
where cSL, cSG, and cLG, respectively, represent the interfacial free energies per unit area of solid–liquid, solid–gas, and liquid–gas interfaces. This equation is valid for the wettability of a homogeneous smooth solid surface.
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.168 1546
J. Mater. Res., Vol. 29, No. 14, Jul 28, 2014
http://journals.cambridge.org
Downloaded: 30 Mar 2015
Hydrophobic coatings, representing an important technology for wettability control, are anticipated for use in various industrial applications such as anti-wetting, antisnow (or ice)-adherence, anti-rusting, and reduced friction resistance by decreasing solid–liquid interaction. Generally, a hydrophobic surface is one on which water forms a round droplet (water CA .90°) that is removed easily. The maxim
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