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Home > Blogs > Anthony Harrington > Cheaper, stronger, faster materials from fractal nano-structures

Cheaper, stronger, faster materials from fractal nano-structures

Cheaper, stronger, faster materials from fractal nano-structures Anthony Harrington

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Disruptive technologies just keep coming. A breakthrough by researchers at the California Institute of Technology (CalTech), reported by Gizmag, which specializes in reporting innovation of all kinds, is set to completely revolutionize the way in which manufacturing and engineering uses materials.

Until now, a material's strength has tended to be quite closely coupled to its density. Moreover the characteristics of each material have been a "given" that engineers have had to work with or work around. Since a material's density, strength and weight are closely coupled, this has meant that strong materials like steel come with a severe weight penalty. One of the Holy Grails in engineering is to find materials that have extreme strength and that are very significantly lighter than current "strong" materials.

The CalTech breakthrough is based on building fractal nano-scale structures with a polymer, using a process called "two-photon lithography" to build the structures. The "fractal" part comes from the fact that the 3D model structures, built up in a CAD design system, consist of a series of self similar nested triangles and polygons (this is the "fractal" part). The researchers use a very finely focused laser to "write" the resulting 3D pattern into the polymer. Wherever the laser touches the polymer it hardens and the rest can then be dissolved away, leaving the "micro-truss" 3D frame intact. The components of the structure produced by the process can be as small as five nano-meters in scale.

Once the researchers have their micro-truss the next step is to coat the structure with their material of choice. The coating is continuous and ultra thin. The polymer frame is then dissolved away, leaving the material with a very different "cellular" type structure to its natural crystalline structure.

This new "cellular" structure gives the material completely new and different properties. Rigid materials can be made ductile, brittle materials such as ceramics can be made deformable, so that when squashed out of shape they will simply rebound to the original form without coming apart or shattering. The exploration of the capabilities of this new way of working with materials is still in embryonic form, but the implications are huge.

R&D Magazine, which also reported the Caltech team's research, quotes Julia Greer, professor of materials science and mechanics at Caltech, on the implications of the research:

"Having full control over the architecture gives us the ability to tune material properties to what was previously unattainable with conventional monolithic materials or with foams. For example, we can decouple strength from density and make materials that are both strong (and tough) as well as extremely lightweight. These structures can contain nearly 99% air yet can also be as strong as steel. Designing them into fractals allows us to incorporate hierarchical design into material architecture, which promises to have further beneficial properties."

Gizmag points out that once researchers solve the non-trivial problem of how to get their production processes up to an industrial scale, the combination of lightness and strength will take manufacturing into uncharted territory and unleash a vast array of new products and building processes.

The flaw in the argument, however, is precisely that it is non-trivial to go from building very small scale nano-structures to building macro structures from these nano scale materials. However, this is basically an engineering problem and once properly posed, it should be capable of being resolved. Just don't hold your breath. The move from the lab to the real world could take a decade or three...

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Further reading on disruptive technologies:

Tags: California Institute of Technology , Caltech , disruptive technology , lithography , materials science , nanostructures , nanotechnology
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