Sonochemical Routes to Superhydrophobic Soft Matter Coatings: Comparing Silica and Copper Oxide Coatings on Polyester Fabric

Reliable and long-lasting water repellency, ideally based on fluorine-free additives, is a desired utility in functional textiles, e.g., for outdoor active wear, workwear, and even protective medical garments. To date, such coating treatments have usually been accomplished by pad-dry-cure, electrolysis, or similar methods that tend to be time-consuming and often yield unsatisfactory coating results. In this study, hydrophobic-coated polyester substrates were prepared using a sonochemical coating process. Comparisons were made between the performances and associated morphological variations of amorphous nano-dimensional silica versus nanocrystalline cupric oxide hydrophobic coatings, which were separately made and successfully loaded, via a random distribution, onto mesoporous polyester-woven fabric substrates. Shorter sonication times seem to allow for retention of preformed morphologies into the subsequent coating patterns. The nanocomposite coatings and their components were characterized using Xray diffraction (XRD), attenuated total reflectance-infrared Fourier transform infrared (ATR-FTIR), SEM, scanning electron microscope (SEM), UV-vis, dynamic light scattering (DLS), and Raman spectroscopy measurements. Almost all coatings displayed highly hydrophobic static water contact angle values -for CuO, these values further increased with time, a rarely reported aging effect thought due to the presence of mixed oxides that likely formed in the coating due to the spallative ultrasonic approach. In addition, the efficacy of these hydrophobic semipermeable fabrics to hexane-water mixture separations, with varying concentrations of Na2SO4, was found to be >99% for optimized membranes, with an associated permeation flux of similar to 5.9 +/- 2 L m-2 h-1, a water content of similar to 0%, and a salt rejection capability of similar to 94%. Thus, non-fluorine-containing sonochemical coating formulations and processes are ideal in the coating of soft matter, polymeric textiles.