A comparative study of alkyl chain silanes and poly dimethyl siloxane liquid-like brushes as PFAS-free liquid-repellent fabric coatings

• Published in: Progress in organic coatings 2024-10, Vol.195, p.108670, Article 108670
• Main Authors: Bagheri Kashani, Mohammad, Rahimi, Bahareh, Morose, Gregory, Salierno, Gabriel, Kumar, Jayant, Nagarajan, Ramaswamy
• Format: Article
• Language: English
• Subjects: Fabric substrate; Liquid-like coating; Liquid-repellency; Long chain silanes; PFAS; Siloxane
• ISSN: 0300-9440; 1873-331X
• DOI: 10.1016/j.porgcoat.2024.108670

Liquid-repellent fabrics have attracted significant attention due to their resistance to hazardous chemicals and reduced maintenance cost. Traditionally, Poly-Perfluoroalkyl substances (PFAS) have been widely used due to their intrinsic low surface energy, which renders them omniphobic (oil and water-repellent) properties. However, due to health hazard issues, there is a growing movement to phase out PFAS use in consumer and industrial products. Recent studies showed that coating low-surface tension flexible brushes to a flat glass substrate, results in the formation of liquid-like slippery surfaces, which impart repellency to various liquids. In this study, two PFAS-free liquid-like coatings were covalently attached to the porous, rough surface of cotton fabric: long alkyl chain silanes, and a hydrolysable trimethoxy silyl polydimethylsiloxane (TMS-PDMS). PDMS is non-toxic, biocompatible, and cost-effective. Importantly, it provides low surface energy of approximately 20 mN/m and has the added benefit of a very low glass transition temperature (Tg = −127 °C), creating a highly smooth structure on the surface. Long alkyl chain silanes also feature low surface energy and flexible brush structures that offer a slippery surface. Silanes with different carbon chain lengths and PDMS brushes with different molecular weights were evaluated. PDMS-treated fabric with MW = 3600 g/mol (F-3600) and fabric treated with n-dodecyl triethoxy silane (FC12) showed superhydrophobic properties with a water contact angle>150° and oil repellency to castor oil with contact angle>80°. The mechanical properties of the PDMS-treated fabrics were comparable or even superior to the control sample. Using a novel toxicity assessment method (P2OAsys), linear PDMS demonstrated a moderate toxicity score of 4.5, in contrast to silanes, with a high toxicity score > 6, and PFAS>8. •Novel PFAS-free omniphobic fabric coatings are compared: long-chain silane and PDMS•The coatings have facile application methods and maintain mechanical properties•Durable liquid-like brushes on fabric show omniphobicity and alcohol repellency•Coated fabrics exhibit liquid-repellency even after abrasion and washing cycles•Both omniphobic coatings were less toxic than PFAS (P2OAsys toxicity assessment)