Urethane-acrylate based Polymeric Superhydrophobic Coatings

Abstract

The study of self-cleaning lotus leaf surface in 1997 by Barthlott and Neinhuis combined with the knowledge of surface wetting phenomenon investigated by Thomas Young, Wenzel, and Cassie-Baxter paved the way for the development of artificial superhydrophobic surfaces. The novel surfaces exhibited immense application potential and ability to solve numerous ubiquitous challenges by functioning as self-cleaning surfaces, demonstrating anti-corrosion, anti-icing, anti-fouling, and drag reduction properties, and ability for oil-water separation, and material degradation prevention. Several fabrication methods have been implemented in literature to develop superhydrophobic surfaces by utilizing materials such as metals, ceramics, polymers, and composites. However, the importance of polymers in the development and commercialization of durable superhydrophobic surfaces is often overlooked. The use of polymer binders such as cross-linked polyurethane-poly(methyl methacrylate) (PU-PMMA) system demonstrate significant durability enhancement of superhydrophobic surfaces compared to bare low surface energy coatings. However, the long-term storage stability of colloidal dispersions of such polymeric binders is an essential requirement to develop superhydrophobic coatings with consistent properties. In this work, the significance of polymers is highlighted by reviewing the numerous techniques involved in the fabrication of superhydrophobic surfaces and their potential to achieve novel properties such as reversible switching, durability enhancement, flame retardancy, UV and chemical stability due to the ability of polymers to be synthesized with tunable properties. Further, the colloidal stability and gelation prevention of PU-PMMA is investigated by varying the isocyanate to hydroxyl index (NCO:OH) and examining the role of water in the system while considering the side reactions of isocyanate-based urethane systems. In addition, the study of rheological and mechanical behaviour of the urethane-acrylate system for formulations with varying water content further explains the colloidal stability and gelation of PU-PMMA system via packing theory. Lastly, a green eco-friendly aqueous poly(urethane-acrylate) system is synthesized as a sustainable alternative for solvent-borne PU-PMMA colloid while completely eliminating the use of volatile organic compounds and exhibiting excellent coating durability and superhydrophobic performance. Show more