Silica Percolated Ionic Dielectric Elastomer with High Electromechanical Energy for Soft Robotic Application

Efforts to introduce soft actuators based on ionic electroactive polymer (i-EAP) in futuristic soft robotic systems are steadily underway. The i-EAPs offer many advantages for improving the performance of soft actuators through lightweight, flexibility, a straightforward manufacturing process, and low power consumption. Despite these advantages of i-EAPs, there are some limitations to their use in various soft robotic applications. Among them, a critical limitation is that i-EAP based actuators have low actuation force due to the flexibility of the material. To overcome this limitation, many studies have been attempted to improve the mechanical modulus of i-EAPs. However, improved modulus of materials reduces the flexibility, which inevitably decreases actuation strain. Therefore, these endeavors have delayed their implementation into soft robots due to the conflicting relationships between force and strain of i-EAP actuators.<br/>In this study, we introduced an innovative approach to overcome the trade-off relationship between force and displacement in soft actuators based on ionic electroactive polymers (i-EAP). We present a novel material referred to as an ions-silica percolated ionic dielectric elastomer (i-SPIDER), which exhibits ionic liquid-confined silica microstructures that effectively resolve the chronic issue of conventional i-EAP actuators. Furthermore, by incorporating resistive polymers (PEDOT:PSS) and using ionic liquids and DMSO as additives, we could control the interface between ionic polymers and electrodes. The i-SPIDER is combined with ionic liquid-confined silica microstructures, thus enhancing electromechanical conversion capabilities at low voltage, thanks to improved ion accumulation facilitated by interpreting electrode polarization at the electrolyte-electrode interface. Through these characteristics, we successfully demonstrated that i-SPIDER containing IL-confined silica microstructures shows simultaneous improvement in both force and strain of electrically driven soft actuators by overcoming the chronic conflicting inverse relationship between them. As a result, ion accumulation was improved on the i-SPIDER -electrode interface, achieving a unique combination of high strain (by approximately 1.52%) and force (by roughly 1.06 mN) even at low Young's modulus (merely 5.9 MPa) based on high electromechanical energy density at a low voltage (2 V) compared to conventional i-EAP soft actuators. Additionally, by demonstrating arachnid-inspired soft robots endowed with user-desired tasks through control of various form factors, we have demonstrated the potential for i-SPIDER-based soft robots to concomitantly enhance strain and force, ushering in the next generation of miniaturized, low-powered, low-voltage soft robotics.