Elastic polymer with piezo-effect A rubber power plant

Flexible, organic, thin – properties that aren’t usually associated with power plants or sensors. But a new material developed by Empa researchers is exactly that: a thin, organic, flexible film that generates electricity if stretched and compressed. This rubber film could be incorporated into control buttons, clothing, robots or even people, and monitor activities, record touches or generate electricity when stressed to power implanted devices such as pacemakers, for example.

Thanks to the piezoelectric effect, the specially designed rubber is able to convert mechanical movements into electrical charges. The trick behind the generated current is the internal polarization which changes when the rubber film is mechanically stressed.

This effect is used in sound pick-ups on analogue record players, for instance: the needle is guided through the grooves in the record in such a way as to generate mechanical vibrations. In a piezoelectric crystal, these vibrations are converted into electrical impulses, which in turn can be amplified and transformed into sound waves.

For a long time, the piezoelectric effect was only known for crystals. As these are heavy and solid, the effect could only be used in certain applications. However, Empa researcher Dorina Opris and her colleagues have now succeeded in giving elastomers piezoelectric properties. Nevertheless, the new material is not easy to produce. The rubber is a composite material made of polar nanoparticles and an elastomer (silicone in the prototype). First of all, Yee Song Ko, a PhD student at Empa, has to shape the two materials before connecting them. This yields a thin, elastic film, in which the polar moieties of the nanoparticles are still randomly oriented.

In order to create a piezoelectric material, Song Ko has to introduce an internal polarization using a strong electrical field. To achieve this, the film is heated until the glass transition temperature of the nanoparticles has been exceeded and they change from a solid, glassy state into a rubbery, viscous one. Under these conditions, the polar moieties are oriented by the electrical field. The orientation achieved is eventually frozen by cooling the material to room temperature.