UV-stable photoactive superhydrophobic coatings utilizing “inverse vulcanization” sulfur polymers

Abstract

“Inverse vulcanization” sulfur polymers present an environmentally friendly approach for producing highly water repellent (superhydrophobic) materials. However, exposure to UV irradiation can lead to the degradation of these polymers into hydrophilic compounds, thereby compromising the long-term superhydrophobic properties of the coatings. In this study, 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (TVTSi) was employed to synthesize sulfur polymers (poly(S-TVTSi) capable of withstanding UV exposure while preserving the photocatalytic properties. Employing a central composite design, poly(S-TVTSi) was combined with inorganic nanoparticles (SiO2 and TiO2) to fabricate superhydrophobic coatings. A variation in the materials composition was used to investigate the influence on the properties of the coatings. Including polymer composition (sulfur:TVTSi ratio), roughness agent composition (TiO2:SiO2 ratio), concentration of nanoparticles (roughness agent), and relative amount of poly(S-TVTSi). The concentration of nanoparticles was identified as the main factor affecting the water contact angle (WCA), whereas all factors (above) generally influenced transmittance, photocatalysis, and UV stability. Using a tailored desirability function, this study demonstrated that a high-performing coating exhibited superior UV stability (up to 300 min) and superhydrophobicity (WCA > 150°). The study also identifies a number of coatings with robust superhydrophobicity, maintaining WCA > 150° across extreme pH and varying concentrations of aqueous NaCl. The coatings also displayed versatile photocatalytic activity against diverse organic contaminants of emerging concern in water bodies, such as caffeine and saccharin. The superhydrophobic coatings made with poly(S-TVTSi) surpass the limited UV stability of sulfur polymers. These materials demonstrate a combined long-term superhydrophobic and photocatalytic performance superior to those previously reported, they present a viable alternative polymer for the production of environmentally friendly and durable superhydrophobic materials.