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plant nanotechnology

Started by VEDPRIYA ARYA. Last reply by Nano May 25, 2008. 1 Reply

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Comment by Nano on April 13, 2008 at 3:58pm
Color without dye stuffs: Nano structures by way of self-organization

Some bright, iridescent butterflies are colorful, even though their wings contain no dye stuffs. This color is exclusively produced by the surface structure on the wings. The size of this structuring is in the order of the wave-length of visible light - hence in the nanometer scale - and leads to such a colorful dispersion. This phenomenon in nature is known as "color without dye stuffs" and BASF researchers are also making good use of it: In watery dispersion, containing nano components of a standard size, the color is obtained through their formation of a crystal lattice. The waves of incoming rays of light are scattered over these ordered nano components and are superimposed in such a way that only one defined wave length, that is one color of the incoming white rays, emerges at a specific angle. The important question is: How is the crystalline ordering of the dispersion film maintained during drying in order to produce a stabile and brilliantly colored surface?

In order to use this dispersion to obtain a color effect, the water contained must be replaced by a matrix polymer. Only then can the ordered nano structure remain even after drying. The essential component is the formation of mono dispersed, in other words identically-sized, core shell components in the nanometer scale. If these components are structured in such a way that the core does not form a film, yet the shells form a film during drying, then the matrix water can be replaced by the shell material. If the thickness of the shells and therefore the distance between the nano components changes slightly, this leads to a color shift. A decrease in size of the core-shell components leads to a color shift, when viewed in face angle, from red to yellow then green and even into the blue range. In addition, the color also changes when the film is rotated, because the distance between the components changes. The color of this film depends on the viewing angle, according to the Bragg equation. The film is not bleached with sun light as there are no chemical dye stuff molecules; the color is physically produced instead.

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