Hydrophobic textiles via bio-mimicking fabrication

Textile surfaces having high degree of water repellency or hydrophobicity are highly desirable for many applications. Currently, to achieve hydrophobicity, fluorochemicals are widely applied. Unfortunately, fluorochemicals are extremely persistent and bioaccumulative. Substances such as perfluorooctanoic acid (PFOA) are found widely existed in the environment, in animals, and even in human blood, which causes great concerns to the public. Major fluorochemicals producers will also phase out some of the products in near future. Therefore, in order to produce 'green' and highly effective hydrophobic finishes for textiles, it becomes necessary to explore fluorochemical-free hydrophobic materials. On the other hand, commonly used fluorochemical-free hydrophobic materials such as silicones are significantly inferior to fluorochemicals in terms of degree of water repellency. In order to achieve superhydrophobic surfaces, researchers turned to structures, especially nano- and micro-structures, found in nature for inspiration. Those structures including lotus leaf, Lady's Mantle, and desert beetle, etc. This proceeding firstly provides a critical review of the current state-of-the-art nano- and micro-structure fabrication techniques, their theoretical backgrounds, their advantages and disadvantages. Following the previous work, new methods of achieving superhydrophobic surfaces are reported, including the building of waterdispersible nanocomposites that consist of a silica nanoparticle component and a silicone water repellent component, carbon nanotubes for building a superhydrophobic surface that can repel hot water, and nanosctructures bio-mimicking lotus leaf. These new methods can functionalize textiles and other substrates. While the surface roughness bio-mimick that of the lotus leaf provides nano- or micro-structure, the use of fluorochemicals and silicone component reduces the surface energy so that superior hydrophobicity can be achieved. Among the new methods reported, one is a nonfluorochemical based system and this system is reported in detail. The material synthesis was done through the use of a long-chain aliphatic silane in a transesterification with poly(ethylene glycol). This is followed by the addition of silica nanoparticles with different surface properties to form a nanocomposite sol. The water contact angles (WCA) from the surfaces and textile fabrics treated by the coating of the nanocomposite and its variations were measured, with some samples achieving a larger than 150° WCA. Surface morphology of the nanocomposite treated surface was also examined using SEM.