Smart materials and self-cleaning bathrooms
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The waxy lotus leaf is useful in designing self-cleansing windows. Through a rigorous study of the leaf structure, engineers have arrived at a suitable density and pattern of placing tiny bumps on glass surface. Since they are smaller than a droplet and closely laid, they do not allow the droplets to stay. The drops roll off keeping the surface clean. Self-cleaning paint, ever-sparkling cement and materials with memory... . smart materials can change the way you live.
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RESILIENCE: Water pearls off from the surface of the Lotus leaf (right). Surfaces applied with smart paint never allow water drops to stay. They are kept clean and dry. COURTESY: STOAG
Imagine a self-cleaning bathroom. No more drudgery of scrubbing the wall, floor and the shower curtain. Tiles clean themselves and keep the toilet clean. Surprised? Welcome to the era of smart materials. What is in store are a set of new materials like self-cleaning paint, ever-sparkling cement and materials with memory.
The world of construction has moved beyond brick and mortar. Curtain glass walls and aluminium panels are not the end of material advancement. The construction industry is looking at materials that push their performance. Researchers are mimicking nature and modifying material behaviour that will enhance building function and make maintenance easier.
Wilhelm Barthlott, a German scientist, studied the behaviour of how lotus leaves pearled off the water from its surface. After careful study of the microstructure of the leaf, he patented a technique called the Lotus effect. This technology was built into a new kind of paint with a brand name StoLotuscan colour. When this paint is applied on a surface, it never allows water drops to stay. As a result, the surfaces are kept clean and dry. They give no room for micro organisms to grow. No fungus, no algae to dirty your painted wall.
Effective simulation
Lotus leaves inspired another group of engineers differently. Engineers at Ohio University found the waxy lotus leaf useful in designing self-cleansing windows. Through a rigorous study of the leaf structure, engineers have arrived at a suitable density and pattern of placing tiny bumps on glass surface. These bumps imitate the leaf structure. Since they are smaller than a droplet and closely laid, they do not allow the droplets to stay. The drops roll off keeping the surface clean.
Andrew R. Parker and Chris Lawrence, in the United Kingdom, studied the African Namib beetle to develop a new hybrid surface to harvest water from fog. The Namib beetle lives in the desert and depends on fog for its water. It positions its body at 45 degrees and spreads its bumpy wing against the wind that carries moisture. The moisture collects on the surface as minute droplets, which then combine and roll as a water droplet directly into the mouth of the beetle. The scientists have developed a surface with small-waxed glass beads imitating the betel wings. When held at angle these surfaces can collect water from the fog. These surfaces also come very useful where the temperature difference between inside and outside is significant.
Engineers and scientists now design and engineer materials. The state-of-art advancement is the nanomaterials. Nanomaterials or nanocrystaline materials are those possessing very small sizes of grains in the order of a billionth of meter. When the materials are produced with such small grain sizes, their property changes. They can radically change to provide useful innovations. For example, porcelain that has excellent thermal properties but brittle after nano processing can become so flexible that it can function as tiny spring in a computer and take care of the heat that is produced.
Oxidisation
Italcementi, the big cement manufacturer in Italy, produced a special type of cement for the famed Dives in Misericordia Church project in Rome. Richard Mier, the American architect who designed this church, is known for his obsessive use of white surfaces. The new invention promised him that his designed white concrete surfaces would always remain white, thanks to the new white cement that contains titanium dioxide. Titanium oxide with photo catalytic action breaks various organic air pollutants that touch the cement surface. It constantly oxidizes the pollutants into carbon dioxide. As a result, the pollutants never get a layer to stick to. The surface remains clean and white. The same catalytic properties of titanium oxide are used in some of the buildings in Japan like Marunouchi building to reduce the discolouring of its walls due to pollution.
Two researchers in Australia pushed this concept little further. The photocatalytic of titanium requires sunrays.
Hence such self-cleaning properties of titanium oxide could only be mobilised for external use. Rose Amal and Professor Michael Brungs of University of New South Wales have developed a nano material with titanium oxide that can work with interior light. Lab tests have shown when this material is applied over tiles and curtains they can activate titanium oxide.
As a result, microbes like Escherchia coli are killed and other organic compounds are disintegrated. This, it is hoped, will lead to designing a self-cleaning bathroom.
Memory alloys
Another important discovery are the Shape Memory Alloys. Shape memory alloys are materials that have memory effect or materials that can remember their original shape and geometry. These materials, at a particular temperature, can come back to their original shape even after they are strained or deformed. Alloys such as Nickel-titanium and copper-aluminum-nickel possess these properties. This innovation has found its way into various applications from construction to art and interior.
Nendo, a Japanese product design company, has invented a new lamp called Hanabi. Hanabi in Japanese means fire flower. When the lights are turned on, the heat of the bulb makes this shape-memory alloy spread open as if it is a flower and reveals the light. Applying similar principle, Etienne Krähenbühl and Rolf Gotthardt, an artist and scientist pair, came together to make a sculpture called Onibaba or magical reeds. Thin oxidized plates were planted on the floor. When visitors came closer, the reeds raised and a path to move through was revealed. When the visitors left, the reeds fall back to cover the ground. A bunch of shape memory alloy wires does this trick to everyone's amusement and wonder.
These smart alloys are also used to produce composite concrete structures. In thin walled members pre-stressing has been hitherto not possible. Now a new method embeds smart alloy wires in mortar, making pre-stressing possible.
The flip side of all this is the high embedded energy value and cost of the material. What is also less known is the nature of waste they would produce. However, this creative step gives hope for a smart and constructive future.
A. SRIVATHSAN
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