MIT engineers have created a new synthetic polymer film that changes its shape when it absorbs water vapor. When the composite film is placed on a surface with even a small amount of moisture, the bottom layer begins to absorb the moisture and the film curls in on itself. Once curled up, the surface of the polymer is exposed to the air and the moisture almost immediately evaporates, causing the film to once again straighten out. This small motion might not seem like a big deal, but these researchers have essentially found a way to use the water gradient to generate power.
Researchers attempting to do something similar have synthesized polymers before but they relied on one single polymer. For this MIT team the key was in the combination of two different polymers; polypyrrole which gives the film its strength and stiffness and the other, polyol-borate, a gel that expands when in contact with moisture.
When in contact with even a small amount of water, this polymer is able to lift glass slides which are 380 times heavier than its own weight and transport silver wire ten times heavier. When combined with a polyvinylidene fluoride film (a piezoelectric material that, when compressed by mechanical force, converts the mechanical energy into electric charge,) it is able to output electricity at about 0.3 hertz with a peak voltage of 1 volt.
While this material may not be on its way to your vacuum cleaner, it could simulate the function of a muscle to control robotic limbs or power nanoelectronic or microelectricalmechanical systems (MEMS) such as carbon monoxide detectors, which currently use small batteries that must eventually be replaced. “If you have this device, you can harvest energy from the environment, so you don't have to replace it very often,” said Mingming Ma, a postdoc at the David H. Koch Institute for Integrative Cancer Research.
In the future this material could potentially be placed above a large body of water such as a lake, ocean or river and be able to draw energy from the environment itself. Currently the researchers are investigating ways of making this new synthetic muscle even more efficient in the hope that smaller and smaller films could power larger devices.
This work was supported in part by AFIRM (the US military’s major effort in Regenerative Medicine that also includes the National Institutes of Health and National Institute of Biomedical Imaging and Bioengineering) and is an excellent example of how diverse funding streams can coalesce to realize the promise of bold new ideas from talented investigators. It is also funded by the National Heart, Lung, and Blood Institute and National Cancer Institute.