Superhydrophobic and water-repellent polymer-nanoparticle composite films

Abstract

The wetting properties of the surfaces of polymer films changed dramatically from the usual inherent hydrophobicity (or slight hydrophilicity) to superhydrophobicity (contact angle, CA > 150°) by embedding oxide nanoparticles into the polymer matrices. The desired hierarchical roughness at the micrometer and nanometer scale was induced in poly(methyl methacrylate), polystyrene, and four poly(alkyl siloxane) films enriched with silica, tin oxide, alumina, and zinc oxide nanoparticles, ranging from 7 to 70 nm in mean diameter. Particles were added in the polymer solutions which were afterward sprayed on various substrates, such as glass, silicon, concrete, aluminum, silk, paper, wood, marble (white), sandstone, and mortar. It is stressed that superhydrophobicity was accompanied by water repellency, as evidenced by the low contact angle hysteresis (CAH < 10°). Consequently, it is demonstrated that the simple suggested method for transforming the wetting properties of polymer films to achieve extreme nonwetting is flexible as it can be effectively applied using different materials, including polymers and nanoparticles of low cost. Moreover, the method can be easily used for the surface treatment of large and various substrates. The effects of the (1) concentration and size of the nanoparticles, (2) chemical nature of the polymer matrix, and (3) treated substrate on the wetting properties of the films were investigated and interpreted using scanning electron microscopy (SEM). Finally, it is shown that depending on the color of the underlying substrate, the superhydrophobic water-repellent polymer-nanoparticle films may have a negligible effect on the aesthetic appearance of the treated substrate.