Super water repellent fabrics produced by silica nanoparticle-containing coating

In this paper, we report on superhydrophobic fabrics (polyester, wool and cotton) produced by a wet-chemical coating technique. The coating solutions were synthesized by the co-hydrolysis of two silane precursors, tetraethyl orthosilicate (TEOS) and an alkylsilane, in an alkaline condition. Without any purification, the as-hydrolyzed solutions were directly used to treat fabrics, and the treated fabrics had water contact angles (CA) as high as 170º and sliding angles (SA) as low as 5º. Three alkylsilanes have been used for the synthesis of the coating solutions, and all contain three hydrolysable alkoxyl groups and one non-hydrolysable alkyl, but with different chain lengths (C1, C8 and C16). It was found that the CA value increased with an increase in the alkyl chain length, while the SA showed a reverse trend. When the functional group had a C16 alkyl, the treated fabric surfaces were highly superhydrophobic, with the CA not being affected much by the fabric type, while the SA values were slightly affected by the original wettability of the fabric substrates. The superhydrophobic feature was attributed to a highly rough surface formed by the particulate coating. Aside from the superhydrophobicity, the influence of the coating on the fabric softness was also examined.