A new polymer film that can generate electricity by drawing on a ubiquitous source - water vapour was created by engineers at MIT.
The new material changes its shape after absorbing tiny amounts of evaporated water, allowing it to repeatedly curl up and down.
Harnessing this continuous motion could drive robotic limbs or generate enough electricity to power micro- and nanoelectronic devices, such as environmental sensors.
"With a sensor powered by a battery, you have to replace it periodically. If you have this device, you can harvest energy from the environment so you don't have to replace it very often," lead author Mingming Ma, a postdoc at MIT's David H. Koch Institute for Integrative Cancer Research said.
"We are very excited about this new material, and we expect as we achieve higher efficiency in converting mechanical energy into electricity, this material will find even broader applications," Robert Langer, the David H. Koch Institute Professor at MIT and senior author of the paper said.
Those potential applications include large-scale, water-vapor-powered generators, or smaller generators to power wearable electronics.
The new film is made from an interlocking network of two different polymers. One of the polymers, polypyrrole, forms a hard but flexible matrix that provides structural support. The other polymer, polyol-borate, is a soft gel that swells when it absorbs water.
Previous efforts to make water-responsive films have used only polypyrrole, which shows a much weaker response on its own.
The film harvests energy found in the water gradient between dry and water-rich environments.
When the 20-micrometer-thick film lies on a surface that contains even a small amount of moisture, the bottom lay