Borrowing an idea from metalsmiths and pastry chefs, researchers have created composite materials containing hundreds of layers that are just atoms thick but span the full width of the material -- a feat that could open new vistas in materials science.
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The work, described recently in the journal Science, could open up wide-ranging possibilities for designing new, easy-to-manufacture composites for optical devices, electronic systems, and high-tech materials.
Materials such as graphene, a two-dimensional form of pure carbon, and carbon nanotubes, tiny cylinders that are essentially rolled-up graphene, are "some of the strongest, hardest materials we have available," said Michael Strano from the Massachusetts Institute of Technology (MIT) .
Therefore, researchers have been searching for ways of using these nano-materials to add great strength to composite materials, much the way steel bars are used to reinforce concrete.
However, the biggest obstacle has been finding ways to embed these materials within a matrix of another material in an orderly way.
These tiny sheets and tubes have a strong tendency to clump together, so just stirring them into a batch of liquid resin before it sets doesn't work at all. The MIT team's insight was in finding a way to create large numbers of layers, stacked in a perfectly orderly way, without having to stack each layer individually.
They used a technique similar to that used to make ultra-strong steel sword blades, as well as puff pastries.
A layer of material -- be it steel, dough, or graphene -- is spread out flat. Then, the material is doubled over on itself, pounded or rolled out, and then doubled over and over again.
With each fold, the number of layers doubles, thus producing an exponential increase in the layering. Just 20 simple folds would produce more than a million perfectly aligned layers.
The MIT team produced composites with up to 320 layers of graphene embedded in them. They were able to demonstrate that even though the total amount of the graphene added to the material was minuscule -- less than 1/10 of a percent by weight -- it led to a clear-cut improvement in overall strength.
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The team also found a way to make structured fibers from graphene, potentially enabling the creation of yarns and fabrics with embedded electronic functions, as well as yet another class of composites.