Know your neighbor? - Short-cuts to crystallization
Scientists at the Max Planck Institute for Dynamics and Self-Organization in Göttingen demonstrate a new route to make artificial opals by allowing complex materials to build themselves.
A pile of sand does not arrange itself like a stack of oranges. Obviously, if the grains come in all sizes, then every grain has a unique size, different from all others, and this makes it impossible to arrange them all into a regular structure, like a crystal. In many applications, this makes the pile or stack worthless. Thus in the field of nano-materials, although we can recreate the iridescence of a butterfly wing, or the play of light of a fiery opal, to do so requires precision-made ingredients – tiny particles that are the size of the wavelength of light – that are all exactly identical in size. Until now.
Laissez faire approach for the lazy physicist or chemist
Here the scientists, including Lucas Goehring from the Max-Planck-Institute for Dynamics and Self-Organization and his colleagues in France, present a laissez faire alternative for the lazy physicist, or chemist. Starting from a broad mix of nano-particles, they show how colloidal crystals can build themselves up, recruiting just the right-sized particles from what is available, and rejecting all the rest. In other words, if the particles interact in the right way – if they can sense their neighbors at a distance, while remaining mobile – then they show how complex colloidal crystals can collect the different parts to build themselves.
Opportunities for new materials
This approach opens the door to the manufacture of a broad range of new materials, with photonic properties, which can grow out of cheap, industrially-produced raw ingredients. It also solves a long-standing problem – such materials have been predicted for decades, but never before seen. Finally, it could show how real opals form, by naturally self-assembling out the ‘soup‘ of particles that would be typically available in a messy geological environment.