Performance enhancement of ionic polymer-metal composite actuators based on radiation-grafted Poly(ethylene-co-tetrafluoroethylene)

To develop a high-performance ionic polymer-metal composite (IPMC) actuator, a series of poly(styrene sulfonate)-grafted poly(ethylene-co-tetrafluoroethylene) (ETS) membranes with ion exchange capacity (IEC) ranging from 2.16 to 3.01 meq/g was synthesized by gamma-radiation grafting. The degree of grafting and the IEC of the ETS were regulated by adjusting the grafting conditions, such as the total irradiation dose and polymerization time. The bending displacement and generating force of the actuators assembled with the ETS membranes increased monotonically in proportion to the IEC. All the prepared actuators exhibited much larger displacement and a faster response than those of the Nafion-based actuators without straightening-back. The excellent performance of the actuators was attributed to the inherent high IEC of the ETS and the consequent high number of available mobile cations and free water molecules in the ETS, leading to large volume expansion on the cathode side. Improved morphological and electrical properties of the platinum layer on the ETS as well as the high bending flexibility of the actuators also contributed to the increase in actuation performance.