Scientists at the University of Georgia have discovered a new way to grow molecular wire brushes that conduct electrical charges. According to the researchers, this discovery is the first step in developing fuel cells for devices such as cochlear implants, prosthetic limbs and pacemakers.
UGA chemist Jason Locklin and two graduate students grew polymer brushes, made up of chains of benzene and thiophene, aromatic molecules sometimes used as solvents, attached to metal surfaces as ultra-thin films. “The molecular wires are actually polymer chains that have been grown from a metal surface at very high density,” said Locklin, who has a joint appointment in UGA’s Franklin College of Arts and Science and on the Faculty of Engineering. “The structure of the film resembles a toothbrush, where the chains of conjugated polymers are like the bristles. We call these types of coatings polymer brushes. To get chains to pack tightly in extended conformations, they must be grown from the surface, a method we call the ‘grafting from’ approach.”
Using a controlled polymerization technique, the researchers laid down a single layer of thiophene as the film’s initial coating, then built up chains of benzene or thiophene. “The beauty of organic semiconductors is how their properties change, based on size and the number of repeating units,” said Locklin, who is a member of UGA’s Nanoscale Science and Engineering Center. Thiophene itself is an insulator, said Locklin, “but by linking many thiophene molecules together in a controlled fashion, the polymers have conducting properties. This technique gives us the control to systematically vary polymer architecture, opening up the possibility for various uses in electronic devices such as sensors, transistors and diodes.” Even under a high-powered optical microscope the ultra-thin films are too small to see, having between 5 and 50 nanometers.
In the future Locklin wants to develop similar applications. For example, his polymer brush technique might be used in a range of devices that interface with living tissue, or “The film itself might be used in transistors-or in photovoltaic devices such as solar cells,” as he said.