Hydrophilic Poly(vinylidene Fluoride) Film with Enhanced Inner Channels for Both Water- and Ionic Liquid-Driven Ion-Exchange Polymer Metal Composite Actuators

This study presents a novel and facile strategy to fabricate a hydrophilic poly(vinylidene fluoride) (PVDF) electrolyte film with enhanced inner channels for a high-performance and cost-effective ion-exchange polymer metal composite (IPMC) actuator. The resultant PVDF composite film is composed of hierarchical micro/nanoscale structures: well-defined polymer grains with a diameter of ∼20 μm and much finer particles with a diameter of ∼390 nm, producing three-dimensional interconnected, hierarchical inner channels to facilitate ion migration of IPMC. Interestingly, the electrolyte matrix film has a high porosity of 15.8% and yields a high water uptake of 44.2% and an ionic liquid (IL, EMIm·BF4) uptake of 38.1% to make both water-driven and IL-driven IPMC actuators because of the introduction of polar polyvinyl pyrrolidone. Compared to the conventional PVDF/IL-based IPMC, both water-driven and IL-driven PVDF-based IPMCs exhibit high ion migration rates, thus effectively improving the actuation frequency and producing remarkably higher levels of actuation force and displacement. Specifically, the force outputs are increased by 13.4 and 3.0 folds, and the displacement outputs are increased by 2.2 and 1.9 folds. Using an identical electrolyte matrix, water-driven IPMC exhibits stronger electromechanical performance, benefiting to make IPMC actuator with high levels of force and power outputs, whereas IL-driven IPMC exhibits a more stable electromechanical performance, benefiting to make long lifetime IPMC actuator in air. Thus, the resultant IPMCs are promising in the design of artificial muscles with tunable electromechanical performance for flexible actuators or displacement/vibration sensors at low cost.