Fluorine-free anti-droplet surface modification

In daily life, many surfaces become contaminated owing to dust/dirt accumulation via air pollution. Self-cleaning surface modification is one of the best ways to address this problem. Therefore, ultra-hydrophobic coatings have garnered significant attention owing to their potential applications featuring water resistance and self-cleaning ability. In the new study, a simple, fluorine-free, as well as eco-friendly technique was utilised to fabricate durable self-cleaning coatings.

This coating material consists of fluorine-free hexadecyltrimethoxysilane-altered SiO₂ nanoparticle (NPs)-coated carbon nanofibers (CNF/SiO₂-HDTMS) and a commercial gelatin based adhesive emulsion. Owing to the presence of the hydroxyl (−OH) functional groups of CNFs, SiO₂ NPs could accumulate on CNFs surface, hence creating hierarchical microstructures that generate air pockets for improved hydrophobicity.

Excellent anti-droplet behavior

In this study, the developed coating was applied onto a polyethylene sheet, glass fiber membrane, and glass via dip coating. These surfaces were targeted due to over-use in day-to-day life as well as in industrial applications such as plastic tents, umbrellas, windshields of vehicles, window and door glasses, skyscrapers, membranes, fabrics or papers.

Interestingly, after the introduction of the adhesive based CNF/SiO₂-HDTMS coating, the superhydrophilic microfiber filter became highly hydrophobic, with a water contact angle of 125°. Similar effect can be seen in case of the modified glass, where the average contact angle was determined to be around 141°. The CNF/SiO₂-HDTMS coated poly bag exhibited excellent anti-droplet behavior with water contact and rolling angles of 136° and 12°, respectively. The self-cleaning coatings maintained anti-droplet behavior even after tests such as sand impact abrasion, and finger touch.

The study has been published in Progress in Organic Coatings, Volume 154, April 2021.