Silica Nanoparticles and Surface Silanization for the Fabrication of Water-Repellent Cotton Fibers

Water-repellent and anticorrosive superhydrophobic cotton fabrics were produced via an eco-friendly water-based coating with core–shell fluorescent silica nanoparticles (SiPs) and subsequent immersion in a mixture of two fluorine-free organosilanes (3-(aminopropyl)trimethoxysilane and trimethoxy(octadecyl)silane). Transmission electron microscopy confirmed the spherical and core–shell structure of SiPs, and Fourier-transform infrared spectroscopy characterized their chemical composition. Scanning electron microscopy with energy-dispersive X-ray spectroscopy confirmed the high coating coverage even after realistic laundering cycles. In confocal laser scanning microscopy, the fluorescent core–shell SiPs were used as probes to characterize the coating coverage on the surface of the cotton fibers. The high fluorescent signal provided by the fluorescent core–shell SiP cores enabled their visualization over large surface areas of the modified cotton fibers, before and after several washing cycles. The hydrophobic property of the cotton fiber treatments was evaluated considering the type of particle coating (monolayer or hierarchization), covalent bond with silanes, and a final curing process. Monolayer coating with fluorescent core–shell SiPs and further silanization yielded cotton fibers with high hydrophobicity and excellent durability (tested up to 10 washing processes), maintaining water contact angle (WCA) values above 150°, repellency grade 3, and lower water uptake (165%) compared to pristine (600%) or silanized cotton fibers (340%). Principal component analysis showed that the silanization process increased the SiP-coated cotton fiber resistance to laundering sustaining nonwetting properties up to 10 washing cycles, which was not observed for SiP-coated fibers subjected to no silanization process. Additionally, the silanized and noncured SiP-coated fibers were tested against solvents and corrosive aqueous media, for which high resistance to toluene, chloroform, and strong acid was observed, with the maintenance of static and dynamic WCAs. Thus, this systematic study allowed us to verify the main factors associated with superior hydrophobicity and durability and achieve an optimized and less toxic approach that combines the deposition of fluorescent core–shell SiPs and binary silanization.