Superhydrophobic cotton by fluorosilane modification

Abstract

Superhydrophobic materials are those having surfaces that are extremely difficult to wet, with water contact angle of > 150°. Since the hydrophobicity of a surface is determined by its chemical composition and topography (surface roughness), the superhydrophobicity can be obtained by lowering the surface free energy (by the treatment with fluorinated or silicon compounds) 1-4 and by enhancing the surface roughness with a fractal structure 5-8 . Cotton, a cellulose-based material, that is greatly hydrophilic, is more benefited when made hydrophobic. Modification of cotton to make it superhydrophobic extends the use of cotton even further to various other end-uses, like water-repellent, self-cleaning fabric or it could even be used in oil-spill clean-up where it would repel the water and absorb the oil. Different approaches have been used to obtain superhydrophobicity on cotton, including coating with different modified silica sols 9 , co-hydrolysis and polycondensation of hexadecyltrimethoxysilane, tetraethoxyorthosilicate, and 3-glycidyloxypropyltrimethoxysilane 10 , or treatment with densely packed aligned carbon nanotubes 11 , and polyacrylonitrile (PAN) nanofibres 12 . This paper reports a very simple and easy method of creating superhydrophobicity on a cotton fabric by lowering its surface energy by coating with a fluorosilane. Commercially available bleached cotton fabric (107 g/m 2 ) was used in all the experiments. A sample size of about 10 × 10 cm was used for the different treatments. 1H, 1H, 2H, 2H-fluorooctyl triethoxysilane (FOS) was purchased from Aldrich.