Superhydrophobicity of Textile Membrane with Hierarchical Structured Roughness

Abstract

Superhydrophobic surfaces have drawn a lot of interest both in academia and in industry because of the usability and their wide applications. Inspired by the extreme wetting states displayed by the natural materials, superhydrophobic surfaces have been widely fabricated by various techniques. In this work, superhydrophobic surfaces were manufactured by the spray-coating the hydrophobized silica nanoparticles on cotton textiles and superhydrophobic polyvinylidene fluoride webs were produced by electrospinning. First of all, superhydrophobic and transparent surfaces on the cotton fabrics have been developed using the silica nanomaterials. Initially, trichlorododecylsilane was treated on the silica nanoparticles to lower the surface energy of the fabric. By simply spraying alcohol suspensions containing hydrophobized silica nanoparticles, the extremely water repellent coatings were formed on the textile fabrics. The effect of three type of alcohol solvent on the hydrophobicity of the coated cotton fabrics were examined by measuring the surface wettability. The treated cotton textiles in methanol exhibited the extremely water-repellent behavior with the water contact angles higher than 170° and the contact angle hysteresis lower than 10°. It proved to be essential to form the hierarchical morphology in achieving superhydrophobicity. Then, highly hydrophobic electrospun poly(vinylidene fluoride) (PVDF) films have been developed from the electrospinning system by controlling the surface morphology. The PVDF was dissolved in a solvent with different concentrations of 8, 12, 16, and 20 w/v% to investigate the effect of the viscosity on the surface roughness and the hydrophobicity of the electrospun webs. The PVDF material was used due to its low surface energy, thus showing the inherent hydrophobicity. By controlling the surface structure by changing the concentrations, the PVDF webs with the hierarchical morphology, both nanometer- and micrometer-sized roughness, were successfully obtained. The beaded fiber structures with nano-sized fibers and micro-scaled beads and the highest roughness factor about 1.2µm were formed and that surface exhibited the contact angles about 150° with the contact angle hysteresis of 11°, and showing good water repellency. The fabricated PVDF membranes also showed the good oil-water separation ability and oil absorption capabilities as well, demonstrating as the stable oil sorbent material. With the excellent mechanical properties, the electrospun superhydrophobic PVDF membrane is expected to be applied to industrial oil-polluted water treatment material.