Direct Assembly of Silica Nanospheres on Halloysite Nanotubes for “Green” Ultrahydrophobic Cotton Fabrics

Abstract This paper presents a sustainable biomimetic approach to create ultrahydrophobic cotton fabrics. Cotton fabrics are modified using biobased raw materials to create multiple scale roughness and low surface energy on their surfaces. Naturally occurring halloysite nanotubes (HNT) are modified by silanization and direct assembly of silica (SiO 2 ) nanospheres on the surface of HNTs. HNTs “decorated” with SiO 2 nanospheres are covalently bonded onto the surface of cotton fabrics, creating a durable multiple scale surface roughness. Surface modified cotton fabrics are further grafted with fatty acid without using any solvent, via esterification. The combination of the hierarchical roughness pattern created on the surface through modified HNT, and fatty acid treatment results in ultrahydrophobic fabrics with water contact angles (WCAs) above 150°. Surface topographies of modified HNT particles and chemical changes are fully characterized. Attenuated total reflectance Fourier‐transform infrared and WCA studies are used to confirm the grafting of modified HNT particles and aliphatic fatty chains on surface of fabrics. The ultrahydrophobic cotton fabrics washed for five standard laundry cycles (25 home washings) show that the ultrahydrophobicity is durable. Moreover, the ultrahydrophobic fabrics are oleophilic, making them suitable for use in oil–water separation, anti‐biofouling and packaging, and other applications apart from water repellent clothing.