The Fabrication of Fluorine-Free Stretchable Superhydrophobic Films Using Inverse Vulcanization Sulfur Polymer

Stretchable superhydrophobic materials have gained attention in recent years though challenges remain for widespread use, including the need for rapid, energy-efficient, high-throughput, and fluorine-free fabrication methods. In this study, a stretchable superhydrophobic material is developed by coating parafilm with inverse vulcanization sulfur polymers. Silica (SiO2) nanoparticles are incorporated to create a Cassie-Baxter wetting state, achieving superhydrophobicity. The sulfur polymers are synthesized using perillyl alcohol (PER) at varying sulfur-to-PER ratios. The optimal coating formulation is determined to be 70 mg mL-1 of polymer, 50 mg mL-1 of SiO2 nanoparticles, and a sulfur-to-PER ratio of 1:1 (50% sulfur and 50% PER). The films maintained functionality when stretched due to controlled fragmentation that preserved the Cassie-Baxter wetting state. Mathematical modeling revealed a scaling relation between fragment area and thickness, showing that thicker layers produced larger fragments, impairing superhydrophobicity. This study also showcase the successful use of more sustainable bio-based solvents (2-methyltetrahydrofuran), where previous reports of similar processes have used chloroform. The fabricated films also demonstrated improved ultraviolet (UV-C) stability (150 min) compared to other sulfur polymer coatings reported in the literature. This coating of flexible substrates presents a simple and environmentally friendly method for producing stretchable superhydrophobic films.