Rare bi-wetting TiO2-F/SiO2/F-PEG fabric coating for self-cleaning and oil/water separation

Abstract

A TiO₂-F/SiO₂/F-PEG coating (TiO₂-F:TiO₂ modified with fluorocarbon surfactant; F-PEG: resin modified with fluorocarbon surfactant and polyethylene glycol) was fabricated via a three-step mild addition polymerization, followed by uniform dispersion of inorganic nanoparticles. The organic fluorine and hydrophilic polyether groups were introduced by surface grafting, in which the fluorinated polymer provided low surface energy. Surface characteristics of TiO₂-F/SiO₂/F-PEG coated polyester fabric were analyzed by contact-angle measurement (CA), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS). Oil/water separation efficiency was proven via thermogravimetric analysis (TGA). SiO₂ particles, as fine as about 200 nm, were dispersed over the fabric with the as-fabricated coating. The hierarchical roughness structure featured two length scales; the microstructure of the polyester fabric and the nanostructure of the inorganic particles. This unique structure brought about a rare bi-wetting property, through which the coating was both super-hydrophilic (θ_water ≈ 0° in air) and super-oleophobic (θ_oil ≈ 146° in air, and θ_oil,max ≈ 164° under water). Oil/water separation efficiency reached 99% solely via gravity-driven separation at room temperature. Furthermore, the coated fabric still maintained 98% separation efficiency after 16 cycles. Moreover, it offered good high temperature resistance, acid and alkali resistance and mechanical tensile strength. The rare bi-wetting ability of the TiO₂-F/SiO₂/F-PEG coating can be expected to contribute to other desirable properties of functional surface materials, such as self-cleaning and oil–water separation.