Static and dynamic hydrophobicity of alumina-based porous ceramics impregnated with fluorinated oil

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.