Self-cleaning superhydrophobic surfaces

New products and new properties of products can be developed by learning from principles and functions in nature. ITV Denkendorf is working in basic and applied science in networks of botanic institutes, chemical companies, textile producers and consumers in different fields on bionic ideas. One of the main focuses of current work with nanotechnology within these networks is the development of self-cleaning superhydrophobic surfaces on textiles. 

The characteristic property of self-cleaning or so-called Lotus-Effect surfaces is the capacity of complete cleaning only by means of water, for example, in the form of rain. The attribute is often called the self-cleaning effect, as there 

There is a variety of applications for fiber-based surfaces with self-cleaning characteristics. This includes outdoor apphcations, such as textile roofs for airports and railways, sunscreen textiles, outdoor clothing, but also indoor applications, which come into contact with water or water-based solutions (Fig. 15.10).  

One of the specific features of textiles in this context is that they readily bring rough structures with at least two topological structure elements represented by the filament s fiber arrangement within the yam stmcture and the yarn arrangement within the fabric stmcture. Subsequent approaches to 

10 Honey droplet on a fabric with self-cieaning surface characteristic. 

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From a commercial point of view, cleaning of windows is expensive and cumbersome, especially if the windows are on a skyscraper. The hydrophilic route to self-cleaning windows has meanwhile been reaUzed by several companies and has been released to the market. How far these windows will be a commercial success remains to be seen. The Germany-based website Lotus-EflFekt.de, dedicated to the commercial application of patented self-cleaning superhydrophobic micro-to-nano structured surfaces, states the following ... 

Furstner R, Barthlott W, Neinhuis C, Walzel P (2005) Wetting and self-cleaning properties of artificial superhydrophobic surfaces. Langmuir 21 956-961... 

The lotus effect has inspired scientists to design superhydrophobic surfaces for applications such as self-cleaning windows and water-repellent clothing. To understand the lotus effect and other phenomena involving liquids and solids, we must understand intermoiecuiar forces, the forces that exist between molecules. Only by understanding the nature and strength of these forces can we understand how the composition and structure of a substance are related to its physical properties in the liquid or solid state. 

The lotus plant grows in aquatic environments. To thrive in such an environment the surface of a lotus leaf is highly water repellent. Scientists call surfaces with this property superhydrophobic. The superhydrophobic character of the lotus leaf not only allows it to float on water but also causes any water that falls on the leaf to bead up and roll off. The water drops collect dirt as they roll off, keeping the leaf clean, even in the muddy ponds and lakes where lotus plants tend to grow. Because of its self-cleaning properties, the lotus plant is considered a symbol of purity in many Eastern cultures. 

Surface wettability is a significant factor in determining the physical and chemical properties of materials. Superhydrophobic surfaces have found application in a variety of settings, including self-cleaning surfaces, prevention of snow sticking, oxidation and heat conduction processes and others [1-3], Considering the... 

Natural superhydrophobic surfaces [1, 2] as observed with leaves of some plants or feathers of some birds, correspond to hydrophobic surfaces whose water contact angle (0) is higher than 150° [3], Such surfaces are sometimes called self-cleaning surfaces since a water droplets will take up the dirt particles and roll off the surface [2], The values of water contact angles cannot be obtained with real surfaces, as... 

UV-Resistant and Superhydrophobic Self-Cleaning Surfaces Using Sol-Gel Processes... 

The amazing water repellent properties of many biological surfaces, especially plant leaves, have prompted great research interest. With certain leaves, when water droplets fall on the surface, they can easily pick up contaminants, roll off the surface and thereby clean the leaves. Because the first observation of this self-cleaning phenomenon occurred on lotus leaves, the effect is generally termed lotus effect . Detailed inspection of the leaves showed that micrometer and submicrometer structures as well as hydrophobic materials exist on the leaf surface. The combination of these factors leads to superhydrophobicity. Wenzel [1,2] showed that surface... 

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