The role of chemical microstructures and compositions on the actuation performance of dielectric elastomers: A materials research perspective

Abstract

Dielectric elastomer actuators (DEAs) are one of the emerging areas of investigation in smart elastomer research and have attracted considerable interests due to their wide‐ranging applications, for instance in automation and soft robotic components. Commonly utilized dielectric elastomers (DEs) such as nitrile butadiene rubber (NBR) and its hydrogenated and carboxylated derivatives along with the dielectric fillers (titanium oxide, barium titanate, etc.) were considered to be one of the most established composite systems demonstrating high actuation performance. When subjected to external electrical field, the DEAs derived from the composites were, therefore, capable of reproducing high energy density and large deformation with fast response time. The recent research emphasizes that tunable material properties eventually triggered the improved actuation performance. The exploration of compliant electrodes fabricated by the conventional and state‐of‐the‐art lithographic methods was also crucial to improve actuation performance for the soft robotic applications. This review summarizes the commonly used DEs and dielectric fillers, their performances and challenges, and outlines the research progress (experimental and theoretical) in the field of actuators. Finally, a brief introduction to DEA‐based soft robotics application is also presented.

Network Formation, Properties, and Actuation Performance of Functionalized Liquid Isoprene Rubber

“…On applying voltage across opposing electrodes, a DE film contracts in thickness and expands in the plane direction, converting applied electrical energy into mechanical energy, which defines the actuation principle of a DEA. The strain S in thickness direction is defined by the following equation introduced by Pelrin et al, where E is the electric field strength, Y the elastic modulus, ε the dielectric constant of the dielectric film, and ε 0 the dielectric constant of vacuum ,, S = ε ε 0 E 2 Y . The expansion–contraction characteristics of DEs are unique, which have been exploited in various studies in an attempt to develop soft actuators and robotic assemblies. Mostly, DEs such as silicone, acrylic, nitrile-butadiene rubber (NBR), , hydrogenated nitrile-butadiene rubber (HNBR), , carboxylated nitrile-butadiene rubber (XNBR), , polyurethane, silicone rubber, , etc., have been reported for potential applications as soft actuators. ,− Among various dielectric elastomers, liquid rubbers offer benefits of fabrication ease, design flexibility, and compositional uniformity. , Such characteristics also made liquid rubbers as attractive materials for emerging fabrication technologies such as the 3D printing process for fabricating DEAs in various geometric possibilities. − The use of liquid rubbers is also advantageous for producing intricate structures such as adaptive fiber–elastomer composites with integrated actuators.…”

“…Electroactive polymers (EAPs) of ionic and electronic types are called “artificial muscles” and have attracted considerable research and innovation interest from the scientific community for soft robotic applications. The electronic EAPs such as dielectric elastomers (DEs) are important materials for soft actuators that exhibit large voltage-induced shape deformations, high elastic energy density, and fast responsiveness. − Such exceptional properties made dielectric elastomer actuators (DEAs) appropriate for many fields of applications such as soft actuators, medical devices, automotive, aerospace, wearable technology, etc. − A DEA comprises a flexible elastomer film sandwiched between two compliant electrodes. On applying voltage across opposing electrodes, a DE film contracts in thickness and expands in the plane direction, converting applied electrical energy into mechanical energy, which defines the actuation principle of a DEA.…”

“… 1 − 4 Such exceptional properties made dielectric elastomer actuators (DEAs) appropriate for many fields of applications such as soft actuators, medical devices, automotive, aerospace, wearable technology, etc. 5 − 7 A DEA comprises a flexible elastomer film sandwiched between two compliant electrodes. On applying voltage across opposing electrodes, a DE film contracts in thickness and expands in the plane direction, converting applied electrical energy into mechanical energy, which defines the actuation principle of a DEA.…”

“…On applying voltage across opposing electrodes, a DE film contracts in thickness and expands in the plane direction, converting applied electrical energy into mechanical energy, which defines the actuation principle of a DEA. The strain S in thickness direction is defined by the following equation introduced by Pelrin et al, 8 where E is the electric field strength, Y the elastic modulus, ε the dielectric constant of the dielectric film, and ε 0 the dielectric constant of vacuum 5 , 9 , 10 The expansion–contraction characteristics of DEs are unique, which have been exploited in various studies in an attempt to develop soft actuators and robotic assemblies. Mostly, DEs such as silicone, acrylic, nitrile-butadiene rubber (NBR), 11 , 12 hydrogenated nitrile-butadiene rubber (HNBR), 6 , 13 carboxylated nitrile-butadiene rubber (XNBR), 14 , 15 polyurethane, 16 silicone rubber, 17 , 18 etc., have been reported for potential applications as soft actuators.…”

Preparation and Characterization of Fluorine-Containing Polyimide Films with Enhanced Output Performance for Potential Applications as Negative Friction Layers for Triboelectric Nanogenerators

“…Typically, a TENG device comprises a combination of triboelectric materials possessing distinct surface electrical potentials, which function as a tribo-positive layer and a tribonegative layer, respectively, to realize the generation and transfer of an electric charge when they come into contact with each other. Therefore, the performance and application areas of the TENG technique are highly related to the designed triboelectric materials, with a high charge density and diversified functions [20][21][22][23][24]. A series of well-known polymers containing extensive amounts of electron-withdrawing groups are widely utilized as a negative friction layer to assemble TENG devices, such as poly(vinylidene fluoride) (PVDF), polydimethylsiloxane (PDMS), polytetrafluoroethylene (PTFE), and polyimide (PI) [25][26][27].…”