Scientists at Georgia Institute of Technology have invented a way to generate tiny amounts of electricity when two different kinds of plastic materials rub against one another. This may offer a new way to produce active sensors to replace technology now used for touch-sensitive device displays.
The flexible polymer materials create a triboelectric generator, which could supplement power produced by nanogenerators that use the piezoelectric effect to create current from flexing zinc oxide nanowires, reports PhysOrg.com. Piezoelectricity is the charge that accumulates in certain solid materials in response to applied mechanical stress. The flexible polymer materials creating the triboelectric generator could provide alternating current from activities such as walking.
“The fact that an electric charge can be produced through this principle is well known,” says Zhong Lin Wang, a Regents professor in the School of Materials Science and Engineering at the Georgia Institute of Technology. “What we have introduced is a gap separation technique that produces a voltage drop, which leads to a current flow, allowing the charge to be used. This generator can convert random mechanical energy from our environment into electric energy.”
To create the generator, Wang’s team placed a sheet of polyester against a sheet made of polydimethysiloxane (PDMS). The polyester donates electrons and the PDMS accepts them. Immediately after the two materials rub together, they are separated, creating an air gap that isolates the charge on the PDMS surface that can be harnessed in a circuit. Repeating the rubbing and separation creates an alternative current.
The technique can be used to create very sensitive pressure sensors (as low as 13 millipascals) for potential use with organic electronic or opto-electronic systems. For example, the force of a feather or water droplet touching the surface of a generator produces a current that can be detected to indicate the contact.
The devices can be made approximately 75 percent transparent, allowing them to be used with touch screens to replace existing sensors. “Transparent generators can be fabricated on virtually any surface,” Wang says. “This technique could be used to create very sensitive transparent sensors that would not require power from a device’s battery.”
Wang says that the production process is simple and low-cost, making it possible to be scaled up for larger electrical production and practical applications. “Friction is everywhere, so this principle could be used in a lot of applications,” he says. “We are combining our earlier nanogenerator and this new triboelectric generator for complementary purposes. This triboelectric generator won’t replace the zinc oxide nanogenerator, but it has its own unique advantages that will allow us to use them in parallel.”
Source: “Polymer Power: Triboelectric Generator Produces Electricity by Harnessing Friction Between Surfaces,” PhysOrg.com, 7/9/12
Dale McGeehon has been a journalist and editor for more than 25 years, covering chemical regulation and testing for Pesticides and Toxic Chemical News and innovations in material sciences for the National Technology Transfer Center. His writing credits include Omni and College Park magazines and The New York Times.