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Dielectric elastomer (DE) actuators have been shown to have promising applications as soft electromechanical transducers in many emerging technologies. The DE actuators, which are capable of large actuation strain over a wide range of excitation frequencies, are highly desirable. Here, the first single-component DE of a triblock copolymer with attractive electromechanical performance is reported. Symmetric poly(styrene-b-butyl acrylate-b-styrene) (SBAS) is designed and synthesized. The SBAS actuator exhibits about 100% static actuation area strain and excellent dynamic performance, as evidenced by a wide half bandwidth of 300 Hz and a very high specific power of 1.2 W g -1 within the excitation frequency range of 300-800 Hz., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Dielectric elastomer actuators (DEAs) are promising soft electromechanical transducers for soft robotics. Fabricating a high‐performance DEA actuated by sub‐kV voltage remains challenging. Here, a facile method not only to fabricate ultrathin dielectric elastomer films of triblock copolymers but also to enhance the dielectric breakdown strength and thus enhance the electromechanical performance is reported. A thick thermoplastic elastomer film of poly(styrene‐b‐butyl acrylate‐b‐styrene) from solution blading is symmetrically pre‐stretched and relaxed at 120 °C to fabricate a freestanding ultrathin DE film. Compared with the pristine DE film of the same thickness (12 µm), the thermally‐relaxed DE film with equally biaxial pre‐stretch ratio 3.5 × 3.5 exhibits increased electrical breakdown strength by a factor of 1.9 (from 43 to 82 V µm−1), maximum actuation area strain by a factor of 1.9 (from 11.7% to 22.4%), and highest energy density by a factor of 5.7 (from 4.5 to 25.8 kJ m−3). The enhancement may be ascribed to the self‐reinforcement of the dielectric breakdown strength due to the morphology change of polystyrene nanodomains from spheres to oblate spheroids. Thanks to the ultra‐thinness, the high electromechanical performance is achieved within sub‐kV driving voltage in all cases. [ABSTRACT FROM AUTHOR]

Dielectric elastomers can generate large voltage-induced deformation and have been widely used as soft actuators. Dielectric elastomer multilayer structures function as bending-type actuators, enhancing their stiffness and ability to resist external loads. Modeling a dielectric elastomer multilayer bending actuator allows analyzing its bending performance, and obtaining the stress and strain distributions in each layer of the actuator. It is of practical importance to develop a simple, yet accurate model. This work develops a model to analyze the electromechanical behavior of the dielectric elastomer multilayer bending actuator with various pre-stretch, material, and structural parameters. We also propose a simplified model for a bilayer slender beam, which is a typical multilayer structure. The simplified model describes the relation between the beam bending curvature and the applied voltage, achieving fast calculation with little accuracy sacrificed. Both the model for the dielectric elastomer multilayer and the simplified model for the bilayer beam agree well with the experiment results, validating the models for practical applications in soft robots, flexible sensors, and smart structures. [ABSTRACT FROM AUTHOR]

The manufacture of 3D mesostructures is receiving rapidly increasing attention, because of the fundamental significance and practical applications across wide-ranging areas. The recently developed approach of buckling-guided assembly allows deterministic formation of complex 3D mesostructures in a broad set of functional materials, with feature sizes spanning nanoscale to centimeter-scale. Previous studies mostly exploited mechanically controlled assembly platforms using elastomer substrates, which limits the capabilities to achieve on-demand local assembly, and to reshape assembled mesostructures into distinct 3D configurations. This work introduces a set of design concepts and assembly strategies to utilize dielectric elastomer actuators as powerful platforms for the electro-mechanically controlled 3D assembly. Capabilities of sequential, local loading with desired strain distributions allow access to precisely tailored 3D mesostructures that can be reshaped into distinct geometries, as demonstrated by experimental and theoretical studies of ∼30 examples. A reconfigurable inductive–capacitive radio-frequency circuit consisting of morphable 3D capacitors serves as an application example. [ABSTRACT FROM AUTHOR]

Dielectric elastomers (DEs) are able to deform significantly in response under an external electric field. DE actuators have promising applications in many emerging fields such as biomimetic robots, haptic devices, tunable lens, and loudspeakers. Practical applications of DE devices are limited by the extremely high electric field and the high pre-stretch. Herein, we have designed and fabricated a new type of soft DE composites of partially reduced graphene oxide (RGO)/polystyrene-b-poly (n-butyl acrylate)-b-polystyrene triblock copolymer (SBAS). An extremely soft SBAS was tailor-made as the elastic matrix. A facile colloidal blending method, i.e. simply mixing the SBAS latex with GO aqueous dispersion, was used to fabricate the nano-structured composite with a segregated network of RGO nano-sheets. The design strategy led to the DE composite film of 1.5 wt% RGO/SBAS owning low modulus (0.51 MPa), high relative permittivity (∼11) and relatively high dielectric breakdown strength (33 kV/mm). The DE composite film exhibited 21.3% maximum area actuation strain at relatively low electric field strength 33 kV/mm without pre-stretch. [ABSTRACT FROM AUTHOR]

Abstract: The inflated elastomeric balloon structures are widely used in engineering fields such as elastomeric actuators and artificial muscles. This study, involving both experiment and modeling, is focused on the prestretch effect on non-linear behavior of inflated short-length tubular elastomeric balloons. In the experiment, the prestretched tubular elastomeric balloon is subjected to air pressure while the two ends are fixed with rigid tubes. The shape evolutions of the tubular elastomeric balloons are illustrated. The non-axisymmetric bulging is observed in the inflated tubular balloon with small prestretch. An analytical model based on continuum mechanics is developed to investigate the inflation behavior of the tubular balloons, and the analytical results agree well with the experimental observation. Analysis shows that snap-through instabilities may happen during the inflation of the tubular balloon. Prestretch along the axis of the tubular balloon can suppress instability during inflation and regulate the reaction force along the axial direction. This work can guide the future application of tubular balloons in elastomeric actuators and artificial muscles. [Copyright &y& Elsevier]

Abstract: When used as resonators, dielectric elastomers are subjected to high frequencies and nonlinear oscillation. The present study is focused on a dielectric elastomer resonator whose dielectric membrane is subject to combined loads of tensile forces and voltages. When the loads are static, the resonator may reach a state of equilibrium. The stability and the natural frequency of the resonator with small-amplitude oscillation around the equilibrium state are analyzed. When a periodic voltage is applied, the device resonates at multiple frequencies of excitation. Pre-stretches and applied static voltages tune the natural frequency and modify the dynamic behavior of the resonator. The membrane may suffer loss of tension and electromechanical instability, causing the failure of the resonator. Safe operation range is identified for failure prevention while actuating the resonator. [Copyright &y& Elsevier]

Abstract: The performance of dielectric elastomer (DE) transducers is significantly affected by viscoelastic relaxation-induced electromechanical dissipations. This paper presents an experimental study to obtain the rate dependent stress-stretch relation of DE membranes (VHBTM 9473) subjected to pure shear like loading and electric loading simultaneously. Stretching rate dependent behavior is observed. The results also show that the tensile force decreases as the voltage increases. The observations are compared with predictions by a viscoelastic model of DE. This experiment may be used for further studies of dynamic electromechanical coupling properties of DEs. [Copyright &y& Elsevier]

Far greater voltage-actuated deformation is achievable for a dielectric elastomer under equal-biaxial dead load than under rigid constraint usually employed. Areal strains of 488% are demonstrated. The dead load suppresses electric breakdown, enabling the elastomer to survive the snap-through electromechanical instability. The breakdown voltage is found to increase with the voltage ramp rate. A nonlinear model for viscoelastic dielectric elastomers is developed and shown to be consistent with the experimental observations. [ABSTRACT FROM AUTHOR]

Dielectric elastomers (DEs) are widely studied and applied as an artificial muscle owing to their combined features of large actuation strain, fast response, high energy density, and low noise. However, scalable fabrication of dielectric elastomer actuators (DEAs) with low driving voltages (100 s of volts) and high mechanical outputs remains challenging, which significantly limits their wider applications. In this work, processable, high‐performance dielectric elastomer (PHDE) ultra‐thin film based multilayer DEAs (PUT‐MDEAs) through an optimized dry‐stacking process are fabricated. The obtained ten‐layer PUT‐MDEAs show actuation at 200 V and reach a maximum areal strain of ≈80% at 800 V. They deliver a blocked force of 0.1 N and an energy density of 22 J kg−1 at 200 V and achieve a blocked force of 0.7 N and an energy density of 50 J kg−1 at 700 V. In addition, large‐area PUT‐MDEAs are fabricated using the scalable dry‐stacking method, and  adopted to build low‐driving‐voltage soft pumps and robotic fish, showing their potential for practical applications. [ABSTRACT FROM AUTHOR]

Dielectric elastomer generators convert mechanical into electrical energy at high energy density, showing promise for large and small scale energy harvesting. We present an experiment to monitor electrical and mechanical energy flows separately and show the cycle of energy conversion in work-conjugate planes. A specific electrical energy generated per cycle of 102mJ/g, at a specific average power of 17mW/g, is demonstrated with an acrylic elastomer in a showcase generation cycle. The measured mechanical to electrical energy conversion efficiency is 7.5%. The experiment may be used to assess the aptitude of specifically designed elastomers for energy harvesting. [ABSTRACT FROM AUTHOR]

Dielectric elastomer generators convert mechanical work into electrical energy. Previous tests on membrane inflation elastomer generators, however, indicated rather low efficiency on energy harvesting. To characterize this phenomenon, an analytical model for viscoelastic dielectric elastomer generators is presented to maximize the energy conversion. The analysis is intended for inhomogeneous fields. The result indicates that viscoelasticity and instabilities during inflation and deflation degrade the efficiency of energy conversion and the specific electrical energy generated per cycle. Rapid loading and unloading, as well as appropriate pre-stretches, are found to upgrade the performances of the dielectric elastomer generators. The analysis may guide the design of dielectric elastomer generators. [ABSTRACT FROM AUTHOR]

The cyclic deformation of VHB 4910 dielectric elastomer is experimentally investigated by performing a series of strain-controlled and stress-controlled pure-shear-like cyclic tests at room temperature. In the strain-controlled cyclic tests, obvious Mullins effect is observed in the first cycle, and continuous stress softening is characterized in the subsequent cycles; the Mullins effect and continuous stress softening are intensified by prescribing larger peak strains and higher strain rates. In the stress-controlled cyclic tests, remarkable ratchetting takes place, and its evolution becomes more significant if higher stress levels, lower stress rates and longer hold time at peak stress are prescribed. Moreover, a partial recovery of residual strain indicates that, besides obvious hyper-elasticity, the VHB 4910 dielectric elastomer also exhibits both recoverable viscoelasticity and measurable irrecoverable visco-plasticity during the cyclic tests. [ABSTRACT FROM AUTHOR]

• A method to ascertain elastomer's glass transition temperature (Tg) under varying extreme hydrostatic pressures is proposed. • In addition to the cooling method, increasing pressure (416.67 MPa) can also induce the glass transition in silicone rubber. • Unlike traditional mechanism, the realization mechanism by pressurizing is adjusting Tg to approach specific temperatures. • The transition mechanisms of elastomer to the glass state by cooling and pressurization are also revealed to be different. • Jointly regulating temperature and pressure can build equivalent extreme pressure environment. The successful exploration of the Mariana Trench, Earth's deepest trench, by soft robots inspired by deep-sea organisms, showcasing the potential of soft robots for extreme deep-sea exploration. However, deep-sea extreme pressure significantly alters the structure and properties of robot materials, affecting their detectability. In this study, to ensure soft robots maintain excellent performance even in such extreme environments, meticulous attention is devoted to these pressure-induced changes before designing them. The results demonstrate that applying pressure (416.67 MPa) can induce the glass transition in silicone rubber (SR) even at room temperature. Unlike the traditional realization mechanism (cooling material to its glass transition temperature (Tg)), the realization mechanism through pressurizing is reported that adjusting the Tg of target material to approach a specific temperature. Furthermore, the different transition mechanisms under the two realizations are also revealed. Based the dynamic analysis of SR under extremely low temperature and high pressure, the glass transition pressure (Pg) is proposed, and the glass transition strategy by jointly regulating temperature and pressure to construct equivalent extreme pressure environment is also investigated. This study, taking SR as the case study, holds significant importance for the future development of extreme pressure-resistant soft robots for extreme environment exploration. [ABSTRACT FROM AUTHOR]

(a) Schematic of a bending DEMES actuator (b) Exploded view of the DEMES actuator and different constituent material layers (c) Fabrication procedures of the soft gripper (d) Printing elastic frame on the membrane based on fused deposition modeling (e) A DEMES soft gripper on its bending state with no voltage applied. • A method facilitates the integration of complex soft structures on the DE membrane without any adhesive. • The optimal finger-like soft DE actuator can generate large actuation with the bending angle about 128°. • FEM simulation results provide an adequately match with experimental data in terms of bending angle and blocked force. In this paper, we develop the novel approach to design and fabricate dielectric elastomer (DE) actuator integrating with 3D printed flexible structures, demonstrating large deformation and multi-functionalities. This technique facilitates the combination of complex soft structures fused on the DE membrane without any extra adhesive. Based on the DE actuator, a soft gripper has been fabricated and characterized in terms of bending angle and blocked force. Finite element method (FEM) simulations precisely predict the electromechanical behaviors, guiding the design of the soft actuator. With optimal design, the finger-like soft actuator can generate large actuation with the bending angle about of 128 °. This study can guide the fabrication and modeling of highly designable and customized DE actuators, which are promising in the applications of soft robotics, flexible electronics, and medical devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dielectric elastomer (DE) films with the capability of post-crosslinking. • The initial modulus of DE films can be continuously improved by 10 times. • DE films with parallel modulus patterns can be used for oriented electroactuation. • The advantage of oriented electroactuation of DE actuators was demonstrated. The oriented actuation of muscles is an important motion form in the locomotion of living beings. Dielectric elastomers (DE) as soft electroactive materials are considered as one of the leading candidates for artificial muscles. However, the electro-actuated deformations of most DE films are uniformly expanded, since synthetic elastomer films are generally mechanically isotropic. Here, we design an elastomer network with reserved double bonds, which allows post-crosslinking in as-prepared isotropic elastomer films with designed crosslinked patterns to spatially modulate the stiffness, and the elastic modulus in the post-crosslinked areas can be continuously increased by an order of magnitude. We reveal that introducing proper numbers of periodic parallel post-crosslinked strips enables the elastomer film to exhibit strong anisotropic mechanical behavior. Furthermore, we simulate and demonstrate the advantage of oriented electroactuation in DE actuators by using DE films with different numbers of parallel strips. Like the dexterous and elegant muscle-driven motions of creatures, our DE films capable of post-regulating mechanical properties can be potentially programmed for achieving complicated electroactuation via designing local crosslinked density and patterns. [ABSTRACT FROM AUTHOR]

Experiments are conducted to test the permittivity of dielectric elastomer composites adulterated with multi-walled carbon nanotube (MWCNT). The results show that the permittivity of dielectric elastomer composites can be significantly improved by adding MWCNT conductive particles. A thermodynamic model is presented to investigate the stability of MWCNT particle-doped dielectric elastomer composites. The theoretical investigation proves that the polarization of MWCNT, the electrostriction deformation and material constants of the elastomer significantly affect the stability of the thermodynamic system. The numerical analysis shows that comparing to ideal dielectric elastomer, the stability of dielectric elastomer composites filled with MWCNT coupling between electrostriction and polarization can be significantly enhanced. [ABSTRACT FROM AUTHOR]

• Low-cycle electro-mechanical fatigue of dielectric elastomers was investigated. • The fatigue life decreases with increasing mean stress and stress amplitude. • An electro-mechanical fatigue failure model was developed. • The configurational stress-based damage predictor unified the fatigue data well. Dielectric elastomers (DEs) often suffer from fatigue failure during electro-mechanical cyclic loading, which significantly constrains the applications of DE-based devices. In this work, we first carried out a series of electro-mechanical fatigue tests, where the pure-shear DE specimen was loaded with a constant voltage and cyclic stress with various stress levels. It was found that the DE under large cyclic deformation is vulnerable to the low-cycle fatigue in the failure mode of electric breakdown, and the fatigue life is significantly affected by the applied stress amplitudes and mean stresses. An electro-mechanical fatigue failure model was then developed to predict the low-cycle electro-mechanical fatigue life of DEs in a pure-shear cyclic loading mode by using a configurational stress-based damage predictor and an electro-mechanically coupled constitutive model. This work is expected to help guide the safe design and evaluation of DE-based devices. [ABSTRACT FROM AUTHOR]

An electro-mechanically coupled visco-hyperelastic-plastic constitutive model is established in this work to describe the cyclic deformation of dielectric elastomers (DEs) by addressing the significant ratchetting and cyclic stress-softening behaviors of DEs resulting from the coupled visco-hyperelasticity, plasticity and electro-mechanical effects. First, a visco-hyperelastic-plastic constitutive model is constructed in the framework of large deformation to incorporate the visco-hyperelasticity and plasticity of DEs, simultaneously. The typical Ogden's formulation is employed for the description of basic hyperelastic response; multiple relaxation mechanisms are adopted to capture the time-dependent viscoelastic part; and a finite plastic flow rule based on the arc-length description is proposed to describe the plastic one. Then, within the framework of nonlinear electro-mechanically coupling approach and by assuming quasi-linear dielectric behavior, the visco-hyperelastic-plastic constitutive model is extended to an electro-mechanically coupled one. Finally, the proposed models are, respectively, validated by comparing the predicted results with corresponding experimental ones of VHB™4910 DE. It is found that the pure mechanical and electro-mechanically coupled cyclic deformation of VHB™4910, including the ratchetting and cyclic stress-softening as well as their dependence on the loading level, loading rate and phase-angle difference of cyclic electro-mechanical loading, can be reasonably predicted by the proposed constitutive models. • An electro-mechanically coupled constitutive model is developed. • Both visco-hyperelasticity and finite plasticity are considered in the mechanical part. • The strain-dependent dielectric behavior is utilized in the electro-mechanical coupling part. • The ratchetting and cyclic stress-softening of VHB™4910 are fairly predicted. • The effect of electro-mechanical coupling on the ratchetting and stress-softening is reasonably predicted. [ABSTRACT FROM AUTHOR]

A series of electro-mechanically coupled cyclic tests at large deformation are carried out to characterize the cyclic deformation of a laterally constrained dielectric elastomer (DE) in this work. In the strain-controlled cyclic tests of the dielectric elastomer (e.g., VHB 4910 DE) with a constant or cyclic voltage, cyclic stress softening occurs and is influenced by the phase-angle difference between the applied cyclic strain and cyclic voltage. In the stress-controlled cyclic tests of VHB 4910 DE with a constant or cyclic voltage, ratchetting (a cyclic accumulation of inelastic strain) takes place; the ratchetting strain is considerably enhanced by applying higher voltage level, higher stress level and lower stress rate, and is also affected by the phase-angle difference between the applied cyclic stress and cyclic voltage. Moreover, the remarkable recovery of residual strain after the cyclic tests demonstrates that the cyclic stress softening and ratchetting of VHB 4910 DE mainly stem from the viscoelasticity. The comprehensive experimental observations are very useful to develop, calibrate and validate an electro-mechanically coupled constitutive model of dielectric elastomers. • Electro-mechanically coupled cyclic tests are performed for the dielectric elastomer VHB 4910. • The cyclic stress softening and its dependence on voltage levels are characterized. • The ratchetting and its dependence on cyclic stress and voltage levels are characterized. • The electro-mechanical coupling during the cyclic deformation is discussed. • The dominant recovery of residual strain after the cyclic tests is observed. [ABSTRACT FROM AUTHOR]