NOVEL ROUTE TO ACHIEVE HIERARCHICAL ORDERING OF COLLOIDAL CRYSTALS

Colours are one of the most striking ways in which Nature showcases her beauty. Be it the vividly-patterned wings of the butterfly, the elegant feathers of the peacock or the myriad-coloured birds—they all enthral, mesmerize and charm each of us alike—from a child to an adult, a layman to a scientist, a writer to a poet.

However, unlike the colours due to dyes and pigments, most of the colours observed in living organisms are primarily due to underlying periodic structures. Nature remarkably self-assembles these structures from individual building blocks that could be as small as a millionth of a millimetre. Apart from their aesthetic appeal, realization of these structural colours has tremendous applications in our everyday life. Structural colours can have a significant impact on modern electronic gadgets such as smartphones and laptops. The display panel of the devices based on structural colours will use the ambient light itself to power themselves, which in turn can also solve the problems of poor visibility of screens in excess glare.

Over the last decades, scientists across the world are striving hard to realize structural colours in laboratory that can mimic the beautiful colours seen in nature. However, the major impediments in realizing them have been the low mobility of the building blocks, namely colloids and nanoparticles, on surfaces. Owing to their large size, these particles do not diffuse significant distances on the surfaces before meeting another one of their kind, so that they would grow further on. For any useful application, tuning of this separation between the growing centres is very crucial.

In a major breakthrough, scientists at the city’s Jawaharlal Nehru Centre for Advanced Scientific Research and Indian Institute of Science have developed a new strategy wherein they can precisely control the spacing between these growing centres. They have taken recourse to soft-lithography to engineer surfaces with inhomogeneous yet periodic structures. With great ingenuity, they have been able to introduce attraction between the building blocks and the engineered surfaces that locomote the building blocks to the desired sites before the ensuing growth could begin. This technique gives a facile control over the growing structures and that too with much-needed simplicity in the growth techniques. These findings that will shortly appear in prestigious scientific journal “Proceedings of National Academy of Sciences, U.S.A. (2016)” are expected to have a crucial impact on the photonics industry.

Chandan K. Mishra, A. K. Sood and Rajesh Ganapathy, _Site-Specific Colloidal Crystal Nucleation by Template-enhanced Particle Transport_, Proceedings of National Academy of Sciences (PNAS), U.S.A. vol 113 (43), 12094 (2016)”.

http://www.thehindu.com/sci-tech/science/Bengaluru-researchers-mimic-nature-to-produce-richer-colour/article16896281.ece

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