Recent approaches to highly hydrophobic textile surfaces

A super-hydrophobic character is increasingly required for high-performance technical textiles in order to attain effective liquid repellence, self-cleaning, uni-directional liquid transport, or to create barrier coatings on fiber surfaces. Accordingly, numerous novel approaches to decrease the surface free energy of fibers have been studied in the last years, either employing wet-chemical finishes based on modem chemical developments such as silane chemistry, nanocomposite structures, or physically applied thin layers. Similar to other branches, textile researchers have also tried to mimic the extreme water repellence of several plant and animal surfaces according to the understanding by Cassie and Baxter. The scope of this paper is to give a critical overview of the principles, advantages and disadvantages of several concepts. While leading to high water or even oil repellence, chemical finishes applied using conventional methods - i.e. dipping or padding and ensuing thermal fixation - mostly fail to withstand influences such as mechanical stress - e.g. abrasion, high tensile forces -, climate, aggressive chemical environments, and high temperatures, to which technical textiles are subjected to in use. This is true for conventional fluorocarbons or novel finishes such as silicones. Here, cross-linked layers of non-polar character prove to be superior. These can either be obtained by deposition of inorganic-organic nanocomposites, e.g. using the sol-gel technique, or by deposition of thin layers by physical methods. With regard to the effects of microrough fiber surfaces, present knowledge indicates an inferior durability due to the destruction of the delicate topography in use. In natural systems such as plants, this effect is overcome by self-healing mechanisms which technical products do not possess. (c) Koninklijke Brill NV, Leiden, 2008.