Small Structures

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Some of the most fascinating natural structures around us are so tiny that we cannot see them with the naked eye. It wasn’t until the invention of the electron microscope in the 1930s by Ernst Ruska that we were able to finally visualize molecules at the cellular level.

Once you get to the nanoscale, forget everything you thought you knew about properties of matter: physical, chemical, electrical, and optical properties all behave differently. This includes color changes (such as nano-size gold particles appearing red) and changes in the ability to scatter light and block UV radiation. Furthermore, due to the ridiculously small scale of nanoparticles, gravity is pretty much a non-issue. Electromagnetic forces on the other hand have the ability to become very powerful at this scale.

These microscopic structures have been of major interest in the field of bioinspiration. One such example is the lotus plant and the subsequently bioinspired product: Lotusan paint.

Left: Lotusan Effect, Right: Microscopic Structures of lotus leaf. Source; Maryanne Alleyne

 The lotus leaf contains numerous microscopic hydrophobic structures. What these structures do is keep water in droplet form, which then slides down the slightly inclined leaves to the center of the flower effectively keeping it from sinking or becoming water-logged. This is termed the “Lotus Effect.” As the water droplet rolls down the leaf, it picks up dirt particles and carries them along with it, keeping the plant clean. This can be better illustrated in the animation that follows:

This natural phenomena has been adapted into a water-resistant paint known as Lotusan Paint

 The Namib Beetle is able to use a similar mechanism of hydrophobic structures located on its elytra to obtain water in the dry Namib desert:

Namib Beetle Water Collection Mechanism. Source: http://sky.scnu.edu.cn/life/class/ecology/image/5/5-8.jpg

Nano structures allow us to see the vibrant colors of the Morpho butterfly:

Source: Maryanne Alleyne

As photons of light pass into and through these nanostructures, some are bounced back providing the viewer with the vibrant colors seen above.

As mentioned earlier, Gecko feet are a well known source of bioinspiration. The pads of a gecko’s foot are lines with millions of tiny bristles, which then each branch off into hundreds more. These tiny bristles are what make contact with walls and other objects upon which the gecko is climbing. But how do they work? Many assumed they behaved sort of like a suction cup, but the truth is they are actually held together by Van der Waals forces. These normally weak electromagnetic forces are much more powerful at the nano level and allow the gecko (and other animals with similar bristle-y climbing mechanisms) to easily traverse a variety of surfaces.

File:Micro and nano view of gecko's toe.jpg

Source: Autumn, K; How gecko toes stick. American Scientist 94, 124-132.

Sources:

http://en.wikipedia.org/wiki/Electron_microscope

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