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No more heat and beat

Metals can now ‘self-assemble’ into form with new technique.

Metal work for 5,000 years has been a processes of ‘heat and beat’ to make new shapes.

Now, Cornell University researchers have developed a method to self-assemble metals into complex forms with structural details about 100 times smaller than a bacterial cell by guiding metal particles into the desired form using soft polymers.

"I think this is ingenious work that takes the fundamental concepts of polymer science and applies them to make metals in a totally novel way," said Andrew Lovinger, the director of the Polymers Program at the National Science Foundation. "In so doing, it opens the door to all kinds of new possibilities."

Led by Uli Wiesner at Cornell University, his team took metal nanoparticles (measuring two nm in diameter) and coated them with an organic material called ligand. Ligands form a jacket around metal atoms, changing their surface chemistry.

The jacketed metal atoms are then put in a solution containing block co-polymers - a kind of nano-scaffolding material. The thinness of the ligands allows then for the metal nanoparticles to be dissolved.

After the ligand-coated nanoparticles and polymers assemble in regular patterns, the material is heated to high temperatures in the absence of air to convert the polymers to a carbon scaffold. The scaffold is then allowed to cool.

Using this process, the carbon scaffold can be etched away with an acid, leaving behind a structured solid metal.

Applications for this type of metal include making more cost effective catalysts for fuel cells and industrial processes.

"The polymer community has tried to do this for almost 20 years," said Uli Wiesner, Cornell professor of materials science and engineering, who reports on the new method in the 27 June, 2008, issue of the journal Science. "But metals have a tendency to cluster into uncontrolled structures."

The research was funded by the National Science Foundation and the Cornell Fuel Cell Institute.

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