Bioinspired process using anisotropic silica particles and fatty acid for superhydrophobic cotton fabrics

Superhydrophobic cotton fabrics having lotus leaf-like dual scale surface roughness were prepared via a 2-step 'green' process. First, silica particles with different shapes were synthesized using a water-in-alcohol emulsion and polyvinyl pyrrolidone (PVP) of different molecular weights (MWs). Lower MW PVP resulted in a combination of spherical and cone-shaped particles while high MW PVP resulted in needle-shaped particles. These anisotropic particles were covalently bonded to the fabrics to create desired permanent surface roughness. Second, fatty acid was grafted using a novel solvent-free grafting process of fatty acid to lower the surface energy of fabrics. Grafting of fatty acid and silica particles onto the fabric surface was confirmed using ATR-FTIR. The facile 2-step process consisting of obtaining surface roughness through silica particles and low surface energy through grafted fatty acid resulted in superhydrophobic cotton fabrics with water contact angles (WCA) above 150 degrees. Fabrics with dual-shaped particles (spherical and cone-shaped) exhibited a higher WCA of 157 degrees while fabrics with single-shaped (needles) particles showed a slightly lower WCA of 153 degrees. Covalent bonding of both particles and fatty acid resulted in highly durable superhydrophobic characteristics. The 'green', fluorine-free process developed in this study can be easily scaled up for other cellulosic materials such as viscose rayon, paper, micro-fibrillated cellulose, etc., to expand their applications in self-cleaning surfaces, water-repellent protective coatings, packaging, polymer composites, electronics and others.