Stretching old material yields new results for energy- and environment-related devices

Simply put, the researchers stretched Nafion, a polymer electrolyte membrane, or PEM, commonly used in fuel cells and increased the speed at which it selectively filters substances from ions and water.

The resulting process could be important to a number of energy and environment-related applications such as any of several industrial processes that involve filtering, including improving batteries in cars, water desalination and even the production of artificial muscles for robots.

The journal Nature Materials published the results in its June 19 issue in the article, "Linear coupling of alignment with transport in a polymer electrolyte membrane," by Jing Li, Jong Keun Park, Robert B. Moore and Louis A. Madsen, all with the chemistry department in the College of Science and the Macromolecules and Interfaces Institute at Virginia Tech.

"I got the idea for some of these experiments after I saw Bob Moore give a talk at the University of North Carolina about Nafion when I was a post-doc there working with liquid crystals," said Madsen, an assistant professor of physical, polymer and materials chemistry who led the study.

In order to improve PEMs, Madsen and Virginia Tech Chemistry Professor Robert Moore studied exactly how water moves through Nafion at the molecular level and measured how changes in the structure of the material affected water flow. They found stretching it caused channels in the PEM material to align in the direction of the stretch, allowing water to flow through faster.

"Stretching drastically influences the degree of alignment," said Madsen. "So the molecules move faster along the direction of the stretch, and in a very predictable way. These materials actually share some properties with liquid crystals--molecules that line up with each other and are used in every LCD television, projector and screen."

"This is a very clever approach which demonstrates the advantages of interdisciplinary materials research and which may offer important benefits to both energy technologies and sustainability of our natural resources," said Andy Lovinger, polymers program director in the National Science Foundation's Division of Materials Research, which funded the study.

Nafion was discovered in the 1960's and is made up of molecules that combine the non-stick and tough nature of Teflon with the conductive properties of an acid. It is one of many PEMs used to filter water and ions that the researchers say could benefit from the stretching process.