Water Repellent Surface Now Available for Wider Variety of Industrial Applications (2009.10.14)
Professor Kijung Yong (Department of Chemical Engineering) and his group have succeeded in developing an original technology utilizing the lotus effect, which may be used toward development of a variety of applications using coated surfaces.
Leaves of the lotus flower have very high water repellency due to the complex, nanoscopic structure of their surface. Superhydrophobic nanostructured surfaces, such as the lotus leaf, have shown potential for a variety of applications, including microfluidics in biotechnology, fog-resistant coatings, impermeable textiles, anti-contamination, and self-cleaning surfaces.
Nanostructures with low surface energies reduce the contact area of water droplets and prevent the penetration of water into spaces between nanoposts of aligned nanostructures under static conditions. However, superhydrophobicity must be maintained under dynamic rather than stationary droplet conditions for practical applications.
Professor Yong and his group conducted a study of the effects of dynamic impacts on tungsten oxide nanostructures having different surface energies due to the adsorption of self assembled monolayers (SAMs) with various alkyl chain lengths. The team also investigated the effects of ultraviolet (UV) irradiation on chemically modified tungsten oxide nanowire arrays, where the photodecomposition of SAMs caused changes in surface energies and the behavior of impinging droplets.
Through the research, three states of wetting – wetting, partial wetting, and bouncing states – were identified through the balance between anti-wetting and wetting pressures, opening up the way for establishment of technology for designing water-repellent surfaces for impinging droplets.
Professor Yong’s group made a change in the characteristics of a surface through two separate methods: by the bottom-up way which synthesizes nano-waves, and by the top-down which exposes the synthesized nano-waves to ultra-violet rays. Using a high-speed camera to monitor the variation of a water droplet’s dynamic behavior depending on different surface energies, the technology was demonstrated suitable for water-dropping daily conditions.
The results of the study were introduced as the cover paper in the October 12, 2009, online issue of Applied Physics Letters (2009, vol. 95, issue 15).