Effect of biaxial tensile extension on superhydrophobicity of rayon knitted fabrics

Abstract

Superhydrophobicity is generally dependent on a material's surface energy and surface roughness, which controls the formation of a stable composite interface with air pockets between the solid substrate and liquid. Therefore, stretching of the nano-structured surface can produce remarkable changes in surface wettability, and may even result in complete loss of surface hydrophobicity. This study aims to develop superhydrophobic rayon knitted fabrics that maintain superhydrophobicity even under biaxial extension. The contact angles (CAs) and shedding angles (SAs) of stretchable rayon knitted fabrics treated with plasma-induced O₂ etching and hexamethyldisiloxane (HMDSO) vapor coating were investigated for various biaxial extensions of the knitted fabrics during treatment and/or measurement. It was shown that the superhydrophobicity of the rayon knitted fabrics, which were plasma-treated in the relaxed state, was reduced when the treated surface was stretched by applying the biaxial tensile extension. However, superhydrophobicity could be maintained under biaxial stretching when the plasma coating was applied in the extended state. In this study, after the fabrics were subjected to plasma etching followed by HMDSO vapor coating under 30% stretching, the rayon knitted fabrics with nanostructured surface exhibited a water CA of 180° and a water-droplet bouncing behavior with a SA of <8° under 50% extension, and their vapor permeability even increased by 17% compared to the untreated specimen. Thus, the developed stretchable self-cleaning rayon knitted fabrics satisfy various clothing material requirements, including superhydrophobicity, mechanical strength, and vapor permeability even under stretched conditions.