Large strain actuation in polypyrrole actuators

A typical limitation of polypyrrole based conducting polymer actuators is the low achievable active linear strains (2 % recoverable at 10 MPa, 7 % max) that these active materials exhibit when activated in a common propylene carbonate / tetraethylammonium hexafluorophosphate electrolyte. Mammalian skeletal muscle, on the other hand, exhibits large recoverable linear strains on the order of 20%. Such large linear strains are desirable for applications in life-like robotics, artificial prostheses or medical devices. We report herein the measurement of recoverable linear strains in excess of 14 % at 2.5 MPa (20 % max) for polypyrrole activated in the 1-butyl-3-methyl imidazolium tetrafluoroborate liquid salt electrolyte. This advancement in conducting polymer actuator technology will impact many engineering fields, where a lightweight, large displacement actuator is needed. Benefits and trade offs of utilizing ionic liquid electrolytes for higher performance polypyrrole actuation are discussed.