Influence of micro and nano-scale roughness on hydrophobicity of a plasma-treated woven fabric

A superhydrophobic fabric surface was fabricated by forming a dual roughness structure in combination with lowered surface energy. The contribution of the innate micro-scale roughness resulting from the waviness of filaments and yarns in a woven fabric on hydrophobicity was investigated in comparison with a smooth film surface. Though the micro-scale roughness coming from the multi-filaments of fabric was conducive in enhancing the hydrophobicity of the surface, the micro-scale roughness itself was not enough to create superhydrophobicity. Thus a nano-scale roughness was introduced by an anisotropic etching employing oxygen plasma etching followed by plasma enhanced chemical vapor deposition. As for the nano-scale roughness, however, it was possible to achieve the superhydrophobicity only with nano-scale roughness, but with a very large aspect ratio of nano-pillar structure. In the presence of dual-scale roughness consisting of both micro- and nano-scale structures, the superhydrophobic characteristic was effectively achieved even at a small aspect ratio of nano-pillar. By adjusting the number of filaments in a yarn and by controlling the plasma process time, it was possible to control the dual-scale roughness of a woven fabric and its wettability. An excessive thinning and lengthening of nano-pillars may negatively affect the hydrophobicity by the collapse and aggregation of pillar tips, and an appropriate processing condition is critical to design a durable superhydrophobic surface.