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Dielectric elastomers (DEs) can act as deformable capacitors that generate mechanical work in response to an electric field. DEs are often based on commercial acrylic and silicone elastomers. Acrylics require prestretching to achieve high actuation strains and lack processing flexibility. Silicones allow for processability and rapid response but produce much lower strains. In this work, a processable, high-performance dielectric elastomer (PHDE) with a bimodal network structure is synthesized, and its electromechanical properties are tailored by adjusting cross-linkers and hydrogen bonding within the elastomer network. The PHDE exhibits a maximum areal strain of 190% and maintains strains higher than 110% at 2 hertz without prestretching. A dry stacking process with high efficiency, scalability, and yield enables multilayer actuators that maintain the high actuation performance of single-layer films.

Summary In the field of skin-attachable electronics, debonding-on-demand (DoD) adhesives triggered by mild, efficient, and accessible stimuli can facilitate repeated usage with negligible damage to the skin. Here, a simple and versatile method has been developed to fabricate biocompatible bonding/debonding bistable adhesive polymers (BAPs) with skin temperature-triggered conformal adhesion and room temperature-triggered easy detaching. Its potential application in a mechanosensitive communication system is also explored. The BAPs are designed by incorporating stearyl acrylate (SA) and tetradecyl acrylate (TA) into a chemically crosslinked elastomer, where a semicrystalline-to-amorphous transition between 26°C and 32°C results in high adhesive flowability and large energy dissipation. An optically transparent and mechanically compliant debonding-on-demand triboelectric nanogenerator (DoD-TENG) is fabricated using the BAP as the DoD substrate, a polydimethylsiloxane elastomer as the electrification layer, and an ion-conductive elastomer as the electrode. Furthermore, the DoD-TENG can serve as a human-machine interface for a self-powered drone navigation system.

Nonvolatile and durable ionogels are emerging and promising stretchable ionic conductors for wearable electronics. However, the construction of reconfigurable and recyclable ionogels with high mechanical robustness, high stretchability, and autonomous healability, while heavily demanded, is very challenging. Here, we present a gradient-responsive cross-linking strategy for preparing a highly stretchable and reconfigurable thermoplastic engineering ionogel (TPEI). The design of both microcrystalline and dense hydrogen bonds in TPEI contributed to the formation of a unique gradient-responsive network. When the TPEI was melt-processed under heating, the microcrystalline network structure was destroyed to form entangled polymer chains, while the high-density hydrogen-bonded network structure was only partially destroyed. The remaining hydrogen-bonded network allowed the TPEI to have a high viscosity for melt processing. When the TPEI was cooled upon melting injection, extrusion, and spinning, the hydrogen-bonded network was rapidly reconstructed in tens of seconds, allowing it to be reconfigured and reshaped, while the microcrystalline network was further reconstructed to improve its mechanical strength and elasticity during subsequent aging. As a result, the TPEI exhibited engineering-hydrogel-level mechanical robustness (>100 kPa), extremely high stretchability (>1000%), wide-temperature tolerance (−20 to 80 °C), and ultrafast self-healability in few seconds. Due to its mechanical adaptability, high ionic conductivity, and reconfigurability, the TPEI was demonstrated to readily work as a self-healable and recyclable stretchable conductor in a wearable skin-inspired sensor for monitoring sophisticated human motions.

Dielectric elastomer actuators (DEAs) feature large, reversible in-plane deformation, and stacked DEA layers are used to produce large strokes in the thickness dimension. We introduce an electrophoretic process to concentrate boron nitride nanosheet dispersion in a dielectric elastomer precursor solution onto a designated electrode surface. The resulting unimorph nanocomposite dielectric elastomer (UNDE) has a seamless bilayer structure with 13 times of modulus difference. The UNDE can be actuated to large bending curvatures, with enhanced breakdown field strength and durability as compared to conventional nanocomposite dielectric elastomer. Multiple UNDE units can be formed in a simple electrophoretic concentration process using patterned electrode areas. A disc-shaped actuator comprising six UNDE units outputs large bidirectional stroke up to 10 Hz. This actuator is used to demonstrate a high-speed lens motor capable of varying the focal length of a two-lens system by 40 times.

In this work, the effect of temperature, in the range of 25 to 250 °C, on deformation twinning in textured polycrystalline pure magnesium (Mg) was investigated. Compression loading was applied perpendicular to the c-axis texture direction. The yield strength and strain hardening rate are shown to drastically decrease with increasing temperature with total suppression of twinning at 200 °C. This behavior is attributed to the decrease in the critical resolved shear stress for prismatic slip and temperature insensitivity of tensile twinning. These results provide a first step in fundamentally understanding the deformation of Mg at elevated temperatures and quantify the mechanisms that lead to their improved formability at elevated temperatures.

Bistable electroactive polymers (BSEP) combine shape memory with large-strain actuation at the rubbery state to achieve rigid-to-rigid actuation. The stiffness of the BSEP is tunable via glass transition or phase changing. The reversible melting-crystallization of the polymer chains in the phase changing BSEP contributes to the stiffness change within a narrow temperature range. A modulus change of more than 1000 folds can be achieved within 3 °C. Additionally, large actuation strains rivaling those of VHB acrylic elastomers can be obtained at the rubbery state. Explorations regarding potential applications of this material have been focused on tactile displays. In one design, Joule heating of a serpentine-shaped compliant electrode coated on a BSEP film, coupled with a pneumatic pressure source has been employed to raise diaphragm dots with 1.5 mm base diameter to heights up to 0.7 mm. The resulting Braille electronic readers could thus be actuated with low voltages.

Creating an artificial muscle has been one of the grand challenges of science and engineering. The invention of such a flexible, versatile, and power efficient actuator opens the gate for a new generation of lightweight, highly efficient, and multifunctional robotics. Many current artificial muscle technologies enable low-power mobile actuators, robots that mimic efficient and natural forms of motion, autonomous robots and sensors, and lightweight wearable technologies. They also have serious applications in biomedical devices, where biocompatibility, from a chemical, flexibility, and force perspective, is crucial. It remains unknown which material will ultimately form the ideal artificial muscle. Anything from shape memory alloys (SMAs) to pneumatics to electroactive polymers (EAPs) realize core aspects of the artificial muscle goal. Among them, EAPs most resemble their biological counterparts, and they encompass both ion-infusion and electric field based actuation mechanisms. Some of the most investigated EAPs are dielectric elastomers (DEs), whose large strains, fracture toughness, and power-to-weight ratios compare favorably with natural muscle. Although dielectric elastomer actuators (DEAs) only entered the artificial muscle conversation in the last 20 years, significant technological progress has reflected their high potential. Research has focused on solving the core issues surrounding DEAs, which includes improving their operational ranges with regard to temperature and voltage, adding new functionality to the materials, and improving the reliability of the components on which they depend. Mechanisms designed to utilize their large-strain actuation and low stiffness has also attracted attention. This Account covers important research by our group and others in various avenues such as decreasing viscoelastic losses in typical DE materials, increasing their dielectric constant, and countering electromechanical instability. We also discuss variable stiffness polymers, specifically bistable electroactive polymers, which, notably, open DEAs to structural applications typically unattainable for soft-actuator technologies. Furthermore, we explore advancements related to highly compliant and transparent electrodes, a crucial component of DEAs capable of achieving high actuation strain. We then cover noteworthy applications, including several novel devices for soft robotics and microfluidics, and how those applications fit within other major developments in the field. Finally, we conclude with a discussion of the remaining challenges facing current DEA technology and speculate on research directions that may further advance DE-based artificial muscles as a whole. This Account serves as a stepping stone into the field of EAPs, which, through the work of researchers worldwide, are positioned as a potential challenger to conventional actuator technologies.