Transparent and superhydrophobic room temperature vulcanized (RTV) polysiloxane coatings loaded with different hydrophobic silica nanoparticles with self-cleaning characteristics

Superhydrophobic coatings based on room temperature vulcanized (RTV) polysiloxane matrix loaded with organically modified silica (ORMOSIL) nanoparticles were successfully prepared using the cost-effective and scalable one-step spraying coating approach. ORMOSIL nanoparticles were prepared by sol-gel treatment at ambient conditions through the reaction between the commercial hydrophilic silica (R200) and octyl-triethoxysilane (R200.OTS), (1H,1H,2H,2H-nonafluorohexyl)-triethoxysilane (R200.NFS) and a mixture of both (R200.OTS/NFS). The functionalization of the silica was followed by Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). Commercial hydrophobic silica particles functionalized with siloxane (R202) and octyl-silane (R805) were also used for comparison. The presence of 20 % of R202 and R200.NFS resulted in coatings with water contact angle (WCA) higher than 160°, sliding angle <5°, high transparency and an effective self-cleaning behavior. Increasing the amount of nanoparticles increased the superhydrophobic response but the translucence decreased. Coatings containing R200.OTS particles presented high translucence and high WCA, but the sliding angle was also high, which limits their use as self-cleaning material.