CONSPECTUS: 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 ioninfusion 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 include improving their operational ranges with regards to temperature and voltage, adding new functionality to the materials, and improving the reliability of the components they depend on. 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 softactuator 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 DEbased 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.

Paper has remained the world's most-widely accessible information medium even as sustainable and reusable paper replacements have attracted increasing attention. Here, an ink-free rewritable paper concept is developed that combines recent developments in photonic crystals, shape memory polymers, and electroactive polymers in a nanocomposite that matches the benefits of paper as a zero-energy, long-term data storage medium, but provides the additional advantage of rewritability. The rewritable paper consists of a ferroferric oxide-carbon (Fe 3 O 4 @C) core-shell nanoparticle (NP)-based photonic crystal embedded in a bistable electroactive polymer (BSEP). Electrical actuation induces large deformation in the z-axis of the nanocomposite, creating distinct color change in the actuated area. This nanocomposite stores high fidelity color images without inks, the images remain stable after more than a year of storage in ambient conditions, and the stored images can then be rewritten over 500 times without degrading. A seven-segment numerical display is also demonstrated.

The synthesis of (Co and Ni) ferrite nanoparticles followed the methods reported in the literature, 1, 2 with the following modifications. Regarding the materials, Benzyl ether (99%), 1,2hexadecanediol (90%), oleic acid (OA) (90%), oleylamine (OAm) (70%), cobalt (II) acetylacetonate, nickel (II) acetylacetonate, iron (III) acetylacetonate were purchased from Sigma-Aldrich Inc. Absolute ethanol and hexane (95%) were purchased from Fisher Chemical.