electroactive polymer

EAP is a polymer actuator that converts electrical power into mechanical force. In principle it consists of a thin layer of very elastic acrylic tape sandwiched between two electrodes.  Once the voltage in the range of several kilovolts is applied between the electrodes, the polymer rubber changes its shape in two ways. 

First, due to the attraction of the opposing charges, the film is squeezed in the thickness direction (up to 380%), secondly, the repelling forces between equal charges on both electrodes result in a linear expansion of the film. 

As a result, after actuation, the film becomes thinner and its surface biggerarea increases.
If the supportive frame is flexible, due to the initial pre-stretching of the acrylic film, the frame bends. After application of voltage, the material expands, and the component flattens out.


EAP on wikipedia