Disarmingly simple, and humorous to watch, the writhing, jumping pieces of polymers are actually doing something serious by turning thermal energy into mechanical energy (the curling and unfurling) and harnessing electricity from it. The application, while still distant, ranges from large-scale commercial power generators to wearable electronics and sensors powered by the evaporation of sweat.
“We are very excited about this new material,” says Robert Langer, the David H. Koch Institute Professor at MIT, and senior author of the paper last month in Science, in a statement. “We expect as we achieve higher efficiency in converting mechanical energy into electricity, this material will find even broader applications.”
The secret is the mechanical properties of the film. The material is composed of two interlocking network of polymers: a hard, flexible matrix providing structural support and a soft gel called polyol-borate. Together, the two harness energy from the difference between dry and wet environments. When the film gel contacts water, it absorbs and swells, curling away from the wet surface. It is then exposed to the air. As the water evaporates, the film starts to flatten again and then the cycle repeats over again. A piezoelectric layer, which generates electricity as it moves, completes the device.
Although the energy is low–the film boasts a power density of less than 1% of a typical battery–this continuous motion is driven by free ambient heat, pointing towards some radically new ways to generate power in the future, says MIT. Eventually, the film could harvest energy from the environment, placed above a lake or river, say, generating electricity on a larger scale.
For now, the major problem is efficiency. “The current efficiency of the materials converting mechanical energy into electricity is low,” said a representative of the research team by email. The team is looking for better piezoelectric materials to convert the film’s motion into current. They’re also testing biomedical applications with electrodes involved with nerve regeneration.
“If we could improve this efficiency,” says the team, “the generator could find broader application.”