Sol-gel processed superhydrophobic plastic surfaces modified with perfluorooctyltriethoxysilane (POTS)

Abstract

Researches about nanomaterials related to properties such as superhydrophobicity, self-cleaning, corrosion and scratching resistance can be directly related to the materials' wettability. This characteristic is quantified by the contact angle made between the surface and a water droplet, in which angles above 90 degrees are considered to be hydrophobic and those above 150 degrees, superhydrophobic. The focus of this work was the development of a superhydrophobic self-cleaning surface, using silica nanoparticles with a particle diameter around 400 nm to 800 nm (produced via sol-gel, referring to the classic Stöber method) functionalized with perfluorooctyltriethoxysilane (POTS) on a polymeric substrate polymethyl methacrylate (PMMA). Four different surface treatment conditions were analyzed: untreated, treated with non-functionalized silica nanoparticles, treated only with POTS and treated with silica nanoparticles functionalized with POTS. For this last condition, a static water contact angle of (150.0 ± 0.44) degrees and a dynamic water contact angle of (7.5 ± 0.38) degrees were obtained, which is a typical value of a superhydrophobic surface. However, the surface treated with POTS alone had a contact angle of 115 degrees. The high contact angle value was due to the low surface energy obtained, which was of (1.45 ± 0.02) dyn/cm. The modified superhydrophobic surface revealed a superior self-cleaning performance by freely rolling spherical water drops on the non-wettable solid surface. The stability of the modified surface has been proven by water jet impact.