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Even molecules have their own waltz

Methane is one of the most abundant organic gases on Earth and safer for the environment when considering it as an alternative fuel to burning petrol or gasoline. But, as it's a gas, storing it under normal pressure inside a fuel tank would only get you 100 meters or so down the road. Now, high-performance computer simulations are helping chemists virtually create thousands of new materials, so they can find the best one to store more methane within a fuel tank.

Last week, it was announced that, Christopher Wilmer, a researcher from Northwestern University in the US, won an honorable mention for his visualization called, 'High density energy storage using self-assembled materials' for the annual International Science & Engineering Visualization Challenge in 2011.

"There are many scientists who never really trust their own results until they can see them in the form of some visualization. Creating this movie was a very strenuous exercise for my so called 'right brain' - there are so many small decisions to make, you simply have to trust your artistic intuition," said Wilmer.

The video begins with a majestic introduction, which is an allusion to Stanley Kubrick's 1968 film, 2001: A Space Odyssey. This memorable scene is the dawn of a futuristic human space age shown with satellites and space stations spinning in a waltz to the symphony 'The Blue Danube' by Johann Strauss II.

But, instead of futuristic space ships, floating atoms and molecules are shown gently coalescing in Wilmer's film.

The film's narrator said, "through the phenomenon of self-assembly, new materials can be designed with atomic precision." One problem that it can help solve is that of finding new materials to better store concentrations of environmentally friendly fuels.

A CGI video showing a collection of new potential methane-storage materials.
This visualization shows how new algorithms perform computational experiments and is redefining the approach to materials discovery, which may influence how research is done by shifting more work that humans used to do onto computers. (Click on the image to watch the video.) Image courtesy Christopher Wilmer.

Forget liquid; it's all about gas

"In President Barack Obama's state of the union address, he mentioned the importance of natural gas vehicles for the US's future. Our work in creating better natural gas fuel tanks will help make this a reality by reducing the cost, and increasing the range, of natural gas vehicles," said Wilson.

Today's fuel tanks can only store large amounts of liquid fuels such as petrol (gasoline). Gaseous fuels like methane are much better for the environment. But, as gas molecules spread out as far as they can, at standard pressure, a tank of methane contains a little over one thousandth the energy of a tank of petrol.

The idea the researchers came up with was to find a material that would enable higher densities of methane to be stored.

Multiplying the possibilities

Researchers at Northwestern University created a crystal called NU-100, a self-assembled molecule comprised of an organic chemical and metal copper atoms - a metal-organic framework. Each crystal contains trillions of identical pores that allow methane molecules to get inside, multiplying the surface area for methane storage to 50 million square meters (60 million square yards). But, they thought there must be a better material than NU-100.

Wilmer and his colleagues called upon the QUEST high-performance computer at Northwestern University. They computationally simulated a better material by finding the right organic chemical and metal combination.

"To accelerate the discovery process, I wrote an algorithm that rapidly generates hundreds of thousands of hypothetical materials. This was a unique, but much needed contribution to the research literature," said Wilson. The research was published in Nature Chemistry last year.

He said, "we screened 137,953 materials for storing methane using 750 cores. We had very precise results in less than 72 hours." A chemist in the real world would take years just to create one material. All the materials they created can be found in their online database.

New materials were found that were better than NU-100 for methane storage. Wilson said, ""we found that, independent of the chemical composition - an ideal methane storage material has pores that are 80% empty space; the other 20% is composed of atoms that make up the material."

Now, this computational detective work is being used to find new porous materials for a range of applications such as carbon dioxide capture, chemical separations, hydrogen storage, and better filters for gas masks.

- Adrian Giordani

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