Sevketcan Sarikaya1,Frank Gardea2,Jeffrey Auletta3,Alex Langrock3,David Mackie3,Mohammad Naraghi1
Texas A&M University1,DEVCOM Army Research Laboratory South2,DEVCOM Army Research Laboratory3
Sevketcan Sarikaya1,Frank Gardea2,Jeffrey Auletta3,Alex Langrock3,David Mackie3,Mohammad Naraghi1
Texas A&M University1,DEVCOM Army Research Laboratory South2,DEVCOM Army Research Laboratory3
Conductive redox polymers that change shape in response to chemical reactions can serve as actuators and provide great utility in a variety of technologies, including biomimetic artificial muscles and robotics. Their polymeric nature facilitates direct robot-human interfaces, while the redox-based actuation allows for self-lock in actuation. Despite the benefits of the state-of-the-art redox actuators as artificial muscles, their demonstrated actuation mechanisms, such as the need for liquid electrolytes, external driving voltages and/or extreme environmental pH conditions, poses major challenges for many applications. Herein, we introduce for the first time an all-solid and electrolyte-free redox-induced polymer actuator, which generates motion solely in gas environments. We employed wet-spun polyaniline (PANI), which provides scalable, long, conductive, and flexible micro-size fibers. Catalyst (Pt) coated PANI fibers were exposed to H<sub>2 </sub>and O<sub>2 </sub>environments, leading to actuation behavior. The actuation mechanism was studied and it was concluded that configurational changes occur in PANI due to H<sub>2</sub> being oxidized to H<sup>+ </sup>in the presence of the catalyst on the fiber surface which then reduced the PANI fiber, generating a volume contraction. On the other hand, O<sub>2 </sub>oxidized the polymer by reacting with the reduced PANI in the presence of the catalyst, leading to a volume expansion.<br/>The fibers contracted in H<sub>2</sub> and expanded in O<sub>2</sub> with an actuation magnitude of 3.5% under 1 MPa load. The maximum achieved load was staggeringly high for artificial muscles, a value of 12 MPa (compared to <1 MPa strength of human muscle) with 0.5% actuation. The maximum work capacity the PANI fibers generated was 120 J/kg. The redox-triggered actuation was proven by a change in electrical resistance and polymer color. No temperature change was detected and no external voltage was applied. The gas-driven actuators developed in this work create new avenues for the application of PANI and other redox polymers in soft robotics.