LAUSR

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°. Fabrics with dual-shaped particles (spherical and cone-shaped) exhibited a higher WCA of 157° while fabrics with single-shaped (needles) particles showed a slightly lower WCA of 153°. 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.