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Nafion which was discovered at DuPont in the 1960s is a polymer membrane that conducts ions and water through its nanostructure. This property makes the material important for a number of industrial energy applications, such as fuel cells, organic batteries, and reverse-osmosis water purification.
But the material, which is a polymer electrolyte, has also tickled the curiosity of researchers because they haven’t been able to get the details of how it works. A research team led by chemist Louis Madsen recently described in an article in Nature Materials how they found a way to understand Nafion’s internal structure. In doing so, they discovered how they can tweak the material to make it work even better for various applications.
As Research Division Communications Manager at Virginia Tech News, Susan Trulove, explains:
Nafion is made up of molecules that combine the non-stick and tough nature of Teflon with the conductive properties of an acid, such as battery acid. A network of tiny channels, nanometers in size, carries water or ions quickly through the polymer. “But, due to the irregular structure of Nafion, scientists have not been able to get reliable information about its properties using most standard analysis tools, such as transmission electron microscopy,” said Madsen, assistant professor of physical, polymer, and materials chemistry.
The researchers used nuclear magnetic resonance (NMR) to look at molecular motion. They also applied a combination of NMR and X-ray scattering to analyze molecular alignment within the Nafion membrane. The researchers were surprised to see the polymer line up in places on the nanoscale, “like strands of dry spaghetti lined up in a box,” as Trulove quotes Madsen. The lining up of the polymers produced channels through which water molecules could move.
The researchers saw that the alignment of the channels had an impact on the speed and direction of the movement of the water molecules. But the researchers weren’t prepared for the surprise when they stretched the Nafion to see what happened.
Trulove writes:
‘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.’
Alignment and stretching haven’t been correlated before in polymer electrolytes. If the polymer can be made to better align, its performance can be dramatically improved to produce more energy-efficient processes in fuel cells, batteries, and other applications. The fundamental understanding of Nafion’s behavior also opens doors to designing new polymer electrolytes that act as better batteries and membranes for water purification.
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