Fluorine-free, Nanoparticle Coatings on Cotton Fabric: Comparing the UV-protective, Hydrophobic Capabilities of Silica Nanoparticles vs. Silica-ZnO Nanostructures

Robust, hydrophobic woven cotton fabrics was obtained through the sol-gel dip coating of different nanoparticle architectures; silica and silica-ZnO. For water repellency, average values as high as ~148° and relatively low tilt angles for fibrous fabrics (~12°) were observed. In all cases, this enhanced functionality was achieved with the simultaneous retention of excellent water vapour permeability characteristics (i.e.; less than 10% decrease). By scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, and Fourier-transform infrared spectroscopy analyses, the physico-chemical effects of coatings on cotton fibres were observed. In cases where the photoactive ZnO-containing additives were used, several order of magnitude increases in UV-protective capability were also achieved, that were absent in non-ZnO containing samples. Such water repellency and UPF capabilities were also found to be stable to UV-exposure; resisting the otherwise commonly encountered UV-induced wettability transitions for photoactive ZnO. These results suggest that ZnO-containing silica nanoparticle coatings confer excellent and persistent surface hydrophobicity, as well as UV-protective capability, with realistic potential uses in wearables and broader functional textiles applications.