They were not able to explain why the ionic liquids they tested had piezoelectric properties but suggest that applying pressure likely serves to separate charge within the fluid, allowing some to be released. In some instances, the researchers found changes in how the liquid bent light. Further testing showed that the optical properties of the ionic liquids changed when they released electricity.

They also found that the amount of electricity released was proportional to the amount of pressure applied. To their surprise, they found that this led to the release of electricity. The liquid piezoelectric material was discovered as the researchers applied pressure with a piston to a sample of an ionic liquid in a cylinder. Electricity builds up within them and is released when they are pressed or squeezed. The researchers were studying properties of ionic liquids, which are made from salts with unsymmetrical, flexible organic cations and symmetrical weakly coordinating anions. In this new research, the pair in Michigan found the first known example of a piezoelectric material that exists in liquid form at room temperature.

These materials are currently used in products such as sonar equipment, guitar pickups and cellphone speakers. Such materials get their name due to a property that allows them to hold an electric charge and then to release it when stress is applied. Up until now, all piezoelectric materials have been solid.

Piezoelectric effect