Chemical Approaches for Reliable Superhydrophobic Coatings: Synthesis and Applications

A doctoral dissertation conducted under a convention for the joint supervision of thesis at Aalto University (Finland) and Indian Institute of Technology Madras (India) for the degree of Doctor of Science (Technology) at Aalto University and the degree of Doctor of Philosophy at Indian Institute of Technology Madras.Biologically available surfaces having unique liquid repelling properties have become some of the most intensely pursued materials in the past few years. In this context, several living creatures have already been studied in great detail. Surface roughness (nano/microscale) and chemical functionalities being the underlying reason for such phenomena, artificially designed these surfaces have already proven their application potential in different fields of science and technology, directed to solving many global challenges. Although various methods have been proposed for the development of these bio-mimicked surfaces, most of the time, complex multi-step processes, affordability of initial materials, large-scale production, and durability restrict the use of these in day-to-day life. Again, use of organic solvents pose concerns related to safety, environmental pollution, operational cost, storage and transport. From an industrial point of view, these limit the commercialization of these materials and their bulk production. In view of the current scenario, our work mostly focused on the development of coating materials through green and industrially adaptable or feasible ways that provide durable liquid repelling films over diverse array of substrates. Water being an economic and environmentally accepted solvent system, fabrication of these materials was carried out solely in water at room temperature. With regard to primary ingredients, use of affordable materials like clay and cellulose enhanced the possibility of scale up. Along with the mechanical and chemical durability of the coated surfaces, application domains of these materials were identified and demonstrated. In the introduction (Chapter 1), evolution of the concept of "bio-mimicry" followed by its influence on the development of liquid repelling surfaces are discussed. Objectives and motivations of the work are presented in Chapter 2. Chapter 3 covers the details of ingredients, synthesis, experiments and fabrication of the working prototypes. Chapter 4 (publication I) & 5 (publication II) focus on the fabrication of waterborne superhydrophobic coating materials from cellulose nanofiber and clay. Fabrication of durable multi-functional waterproof paper was demonstrated for both cases, needed for various upcoming technologies including microfluidics and various paper-based technologies. In addition, publication II showed the under oil superhydrophobic property of the coated material. Chapter 6 (publication III) reports the fabrication of transparent solid slippery surface and its use in atmospheric water capture through a working prototype. Chapter 7 summarizes the above-mentioned results and gives a future perspective on this research area. We believe that the methodologies and materials presented here can be successfully implemented to various technologies or translated to useful products or devices that will be helpful for human civilization.