ORNL discovers amazing electrical properties in polymers

September 26, 2011
Piezoelectric properties

Piezoelectric properties in non-polar block copolymers are found to be up to an order of magnitude higher compared to classic piezoelectric materials (credit: ORNL)

Researchers at Oak Ridge National Laboratory (ORNL) have discovered a material that has 10 times the piezoelectric effect of crystals and ceramics, making it suitable for perhaps hundreds of everyday uses.

ORNL’s Volker Urban and colleagues at Technical University Aachen in Germany noticed the reverse piezoelectric effect (creating a mechanical strain by applying an electrical voltage) while conducting fundamental research on polymers.

“We thought about comparing the effects that we observed to more ‘classic’ piezoelectric materials and were surprised by how large the effects were by comparison,” said Urban, a member of the Department of Energy lab’s Neutron Scattering Science Division.

Until now, scientists did not believe that non-polar polymers were capable of exhibiting any piezoelectric effect, which occurs only in non-conductive materials. This research, however, shows as much as 10 times the measured electro-active response as compared to the strongest known piezoelectric materials, typically crystals and ceramics.

“We observed this effect when two different polymer molecules like polystyrene and rubber are coupled as two blocks in a di-block copolymer,” Urban said.

Temperature-dependent studies of the molecular structure revealed an intricate balance of the repulsion between the unlike blocks and an elastic restoring force found in rubber. The electric field adds a third force that can shift the intricate balance, leading to the piezoelectric effect.

“The extraordinarily large response could revolutionize the field of electro-active devices,” said Urban. He listed a number of examples, including sensors, actuators, energy storage devices, power sources and biomedical devices. .

Ref.: Pester et al., Piezoelectric Properties of Non-Polar Block Copolymers, Advanced Materials, 2011 [doi: 10.1002/adma.201102192]