Enhanced Marangoni flow to fabricate uniform and porous SiO 2 films: Toward superior high transparency, antifogging, and self- cleaning properties

Fogging on transparent substrate greatly impacts transmittance, causing inconvenience and potential hazards. Increasing surface roughness to enhance hydrophilicity often reduces transmittance. Here, by enhancing the Marangoni flow to inhibit the coffee-ring effect during SiO 2 droplet drying, we propose for the first time to manufacture superhydrophilic and high-transmittance coatings with porous structures on various substrates, including glass and resin. This approach relies on a simple, potentially large-scale ultrasonic spray method to enhance the Marangoni flow of SiO 2 dispersion with different particle sizes by adding multiple surfactants to reduce the surface tension of the dispersion. The water contact angle of the SiO 2 film decreases to below 5° within 0.5 s, imparting anti-fogging properties to the substrate. The film exhibits a transmittance of 93.1 % at 580 nm, surpassing the inherent 90.8 % transmittance of the bare glass. Notably, the film shows remarkable self-cleaning properties due to potent hydration from eco-friendly SiO 2 nanoparticles and the porous structure. Owing to the hydrogen bonding between tightly packed small-sized SiO 2 particles as well as between the particles and substrate, the surface morphology of the film on glass remains intact even after washing, and soaking. The porous SiO 2 film, with a contact angle dropping to below 5° within 0.5 s, maintains its superhydrophilicity even after being exposed to high temperatures, UV irradiation, and humidity conditions. The simple production process of the porous SiO 2 films offers a promising method for preparing high-transmittance anti-fogging films with significant industrial potential.