Nano in Nature How can we be covered in water and not get wet? To answer this question, nanoscientists turned to the lotus flower. It was noticed that the striking white flowers of the lotus plant stayed dirt free and dry even after being submerged in muddy river water. This helps the lotus in two ways: • • Stops bacteria sticking to the surface. Keeps the lotus cool. How does the lotus keep clean? The Lotus leaf has two interesting features: • The surface of the leaf is covered in a waxy material which makes it water fearing or hydrophobic. To understand the second feature we have to take a And closer… closer still… closer look… • The surface of the lotus leaf is actually quite rough. • The projections increase the surface area reducing the amount of contact water droplets have with the surface. When water falls on of a leaf and it clumps form The combination of the the surface waxy coating roughtogether surfacetoallow large droplets.to roll right off taking dirt and micro-organisms that the droplets sit on the surface with them. How does this benefit us? We can create surfaces that stay dry and clean in the same way as the lotus leaf. Self cleaning windows Waterproof clothes But some animals are doing the opposite! • Instead of shedding water the Namib Desert Beetle uses nanostructures to capture it. • A combination of hydrophilic ridges and hydrophobic furrows allows collection of moisture from fog. • By applying this idea to buildings we could trap moisture and use as a water source. What do you need to walk upside down on the ceiling? To answer this question, nanoscientists turned to the • Geckos have the amazing ability to cling to any surface at any orientation. • This is due to the structure of their feet which maximises surface area. A closer look • The soles of geckos’ feet are made up of overlapping lamella. • These lamella are covered with tiny hairs called setae. • Each setae branches out into hundreds of spatula shaped structures. How does a gecko stick? • Most Geckos’ surfaces feet are when flexible you look enough at them to fit into appear the nooks smooth and but at a molecular crannies of any level surface. they can be quite rough. •• At such close contact, attractionall called ‘Van der Objects may look like forces they’reoftouching the surface but Waals’ they areforces not. arise between the setae and the surface creating grip. Gecko glue • Scientists are taking inspiration from the nanofibres in geckos’ foot hairs to develop adhesives that will bind to wet and dry surfaces. • Adhesives made from carbon nanotubes which imitate the setae on geckos’ feet have been developed. To answer this question, nanoscientists turned to the Can we make fibres stronger than steel? How strong is spider silk? • Very strong! • It is the material with the highest known strength, about 5 times that of steel of the same weight. • It is also elastic; spider silk can stretch up to 10 times its own length. More about spider silk • Spider silk is produced from about six silk glands beneath the spider’s abdomen. • The silk consists of protein molecules, long chains comprising thousands of amino-acid elements. • The protein is formed as a liquid by silk glands and squeezed out -the liquid thread hardens as it leaves. Spider goat? • Reports that goats have been genetically modified to secrete silk proteins in their milk. • The milk from the goats was made into a superstrong silk strand. • The thread could be weaved to make strong materials. Caterpillar cocoons • The fibres in caterpillar cocoons are almost as strong as steel. • In CRANN, researchers are taking inspiration from these cocoons. • They are synthesising fibres that are stronger than steel but 5 times lighter - by mixing plastic (PVA) with carbon nanotubes. What type of materials? • Ultra-tough bullet-proof vests. • Sports equipment. • Aeronautics industry. • Car parts. • Household goods. To answer this question, nanoscientists turned to the How is light manipulated at the nano-scale? But first colours… • Colours of some materials are determined by a chemical pigment that absorbs some light and reflects the rest (“chemical colour”). • For example, chlorophyll in plants absorbs light in the blue and red part of the spectrum but reflects green. • This is why leaves appear green. Physical colour… • An object can change colour when the light interacts with the physical structures (“physical colour”). • When light waves strike a transparent surface some of the light is reflected. A few light waves penetrate the material and reflect off the bottom of the surface. These waves pass upwards and re-join the original waves. •• When When the the crests crests of of the the reflected reflected waves waves do they ‘outand of phase’ and linenot upline theyup are ‘in are phase’ destructive constructiveinterference interferenceisisobserved. observed.The waves cancel each other out colours and colours The waves combine and the appear appear dimmer. brighter. The Morpho butterfly • The extraordinary colours on the butterfly come from the interaction of light on the nanometre size structures on their wings. • The same effect can be seen on a CD when you tilt it. Let’s take a closer look at the butterfly Here issection a colour clearer image of the thecan scales taken using an AIf cross of of these ridges show The we true take a closer look the wings at scales, bethe seen wenanostructures can when seelight ridges. is The iridescent colours on its wings are not created by electron microscope. The scales on the wings are that reflect the The microribs are shaped like Each passed ridge through is light. approx. the 800 wing nm butwide not and reflected. contains The blue morpho butterfly is native of central and south pigments, but by the way light interacts with the nano arranged tiles onisaknown roof. is approx. 70 x evergreen trees (short branches atscale the long branches structures thatEach reflect thetop light. America,like the male for its iridescent blue colour. structures on the scales. 200 µm. at the base) allowing for wings’ multiple reflections. Applications Scientists are using their understanding of the structure of butterfly wings to develop new fabrics, dye-free paints, and anti-counterfeit technologies for currency. Summary • Natural nanomaterials are inspiring scientists! • Lotus effect: – Self-cleaning windows. – Waterproof clothing. • Gecko feet: – Adhesives. • Spider silk and caterpillar cocoons: – Stronger, lighter materials. • How many more natural nanomaterials can you remember?