Biomimetics by Primrose Sandy B.;

Author:Primrose, Sandy B.; [Primrose, Sandy B.]
Language: eng
Format: epub
Publisher: John Wiley & Sons, Incorporated
Published: 2020-06-22T00:00:00+00:00

Figure 4.9 The 2016–2017 Research Pavilion at the University of Stuttgart. The final pavilion after construction (top) and the method of construction by spinning fibres (bottom).

Source: Reproduced courtesy of ICD Institute for Computational Design and Construction, Faculty of Architecture and Urban Planning.

4.3 Self‐Cleaning Surfaces

In the 1970s, Wilhelm Barthlott was the first botanist to study biological surfaces using scanning electron microscopy. His main interest was plant systematics and he was interested to know if the fascinating nano‐ and micro‐structures that he saw could be used for classifying different plant taxa. To study these surface structures the leaves had to be prepared and cleaned. Barthlott soon realized that the leaves of some species were always clean whereas the surfaces of other species were always dirty. Surprisingly, there was a correlation between cleanliness and wettability. The smooth hydrophilic leaf surfaces were markedly dirty whereas the water‐repellent, hydrophobic leaf surfaces with microscale roughness were always clean. A publication detailing these observations went unnoticed outside of a small group of plant taxonomists.

In the 1990s, Barthlott1 and his student Christoph Neinhuis began a detailed investigation on the structural and functional basis of the self‐cleaning ability of certain plant leaves. They chose the lotus plant (Nelumbo nucifera) as their model because its leaves are always clean even though it grows in very muddy water. The cleanliness of the leaves in such an environment is so noticeable that the lotus has become a symbol of purity in many Eastern cultures. Examination of the surface of lotus leaves under a microscope revealed that the surface of the outer layer of cells (epidermis) is not smooth but is bumpy. This bumpy epidermis is covered by a thin layer of wax crystals that are water‐repellent (Figure 4.10). These two properties make the leaf super‐hydrophobic (contact angle >140°) and self‐cleaning. Water falling onto the surface of the leaf forms nearly spherical beads that easily roll off; any dirt clings to the water droplet rather than to the waxy, bumpy surface of the leaf, and so is carried away. It is this complex surface coating that enables the leaf to be self‐cleaning, a phenomenon dubbed the ‘lotus effect’ (now trademarked as Lotus‐Effect®).

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