Dielectric elastomers (DEs) stand out among various soft actuators for their exceptionally fast response and large actuation. A dielectric elastomer can emerge out-of-plane vibration under alternating voltage and change its resonance frequency by adjusting the direct voltage. In this paper, the emerging conditions of the out-of-plane vibration of dielectric elastomer resonator (DER) are obtained by changing the pre-stretch, electrode area and the amplitude of the voltage. Sweep frequency tests are conducted to obtain the resonance frequency of DER, and the modals of the vibration are also obtained by experimental measurements. The nonlinearity vibration phenomenon which appears along with the increase of the amplitude of voltage is analyzed. The resonance mechanism of DER has a high energy exchange efficiency, which has a potential application in soft robot.
Dielectric elastomer (DE) is capable of giant deformation subject to an electric field, and demonstrates significant advantages in the potentially application of soft machines with muscle-like characteristics. Due to an inherent property of all macromolecular materials, DE exhibits strong viscoelastic properties. Viscoelasticity could cause a time-dependent deformation and lower the response speed and energy conversion efficiency of DE based actuators, thus strongly affect its electromechanical performance and applications. Combining with the rheological model of viscoelastic relaxation, the viscoelastic performance of a VHB membrane in a circular actuator configuration undergoing separately constant, ramp and sinusoidal voltages are analyzed both theoretically and experimentally. The theoretical results indicated that DE could attain a big deformation under a small constant voltage with a longer time or under a big voltage with a shorter time. The model also showed that a higher critical stretch could be achieved by applying ramping voltage with a lower rate and the stretch magnitude under sinusoidal voltage is much larger at a relatively low frequency. Finally, experiments were designed to validate the simulation and show well consistent with the simulation results.
In this paper, we developed a new kind of ionic polymer metal composite (IPMC) actuator by doping sulfonated carbon nanotube (SCNT) into Nafion matrix to overcome some major drawbacks, such as low output force and short air-operation time, which restrict applications of conventional Nafion IPMC actuators. Firstly, SCNT was synthesized by coupled reaction of multi-walled carbon nanotubes and azo compounds and then doped into Nafion matrix by casting method. Subsequently, several key parameters of the SCNT-reinforced Nation matrix, water uptake ratio and equivalent stiffness, were revealed and the inner morphology of the membranes were observed by scanning electron microscopy. Finally, the effects of the SCNT on the electromechanical properties of IPMC actuators, especially the actuating performance, were evaluated experimentally and analyzed systematically. The results showed that SCNT was evenly dispersed in Nafion matrix and a small amount of SCNT could improve the performance of IPMC actuators significantly.
The performance of a charge-controlled dielectric elastomer membrane is remarkably affected by the leakage current. Based on a charge-controlled dielectric elastomer configuration, this
paper presents a theoretical study about the effect of leakage current on the performance of a dielectric elastomer membrane by spraying charge to the two surfaces of DE membrane. It is found that all of the stretch, the charge, and the electric displacement reduce gradually with
the time because of the current leakage. The leakage current reduces gradually with the time, and has an abrupt drop in the initial period and becomes gently after a relatively long time.
Based on the results of this paper, we have to keep spraying charge to make up the leaked one to maintain the charge-induced stretch.
Dielectric elastomer is able to produce a large electromechanical deformation which is time-dependent and unstable due to the visco-hyper-elasticity. In the current study, we use a thermodynamic model to characterize the viscoelastic relaxation in the electromechanical deformation and instability of a viscoelastic dielectric. The parameters in the model were verified experimentally. We investigate the time-dependent mechanical deformation, electrical breakdown strength, polarization, and the electromechanical stability which are coupled by viscoelastic relaxation. The results show the electromechanical stability has strong time-dependence, due to the stress relaxation when the pre-stretch is applied.
A multi-physical model of ionic polymer metal composites (IPMCs) is presented in this paper when they deform under
an applied voltage. It is composed of two parts, which describe the dynamic electro-transport and the large deformation
respectively. The first part describes the ion and water molecule transport, the equations of which are derived using the
thermodynamics of irreversible process. Besides the gradient of the electric potential and the concentration usually
considered in the previous models of IPMCs, the hydrostatic pressure gradient is confirmed to be one of the main factors
induced the mass transport. The second states the eigen strain induced by the redistribution of ion and water molecule
and reveals the stress field from micro to macro scale by the method of micromechanics. The elastic stress balanced with
the eigen-stress including the hydrostatic pressure can influence the distribution of ion and water molecule reversely. To
explore the reasonable mechanisms of the relaxation phenomena, various kinds of eigen-stresses are discussed here and
preliminary numerical results evaluating deformation are given based on the classical Na<sup>+</sup> Nafion type IPMC. It's
obtained that the osmotic pressure is an indispensable eigen-stress to explain the complicated deformation.
The electromechanical behavior of dielectric elastomer is strongly affected by the temperature. Very few models
accounting for the effects of temperature exist in the literature. A recent experiment showed that the variation of
dielectric constant of the most widely used dielectric elastomer (VHB 4910, 3M) according to temperature is relatively
significant. In this paper, we develop a thermodynamic model to study the influence of temperature on the instability in
dielectric elastomer by involving deformation and temperature-dependent dielectric constant. The results indicate that
the increase of temperature could improve the actuation stress and the electromechanical instability of the elastomer.
The electrode of Ionic polymer-metal composites (IPMCs) is the key to understand their working mechanisms and
mechano-electrical properties; however, there is little experimental report on the electrode morphologies and their
forming mechanisms. In this paper, several typical IPMC samples with different electrode morphologies are fabricated
by combining various process steps. The influence of the process steps, such as roughing treatment, immersing reduction
and chemical plating, on the electrode surface and cross-section morphologies is investigated by SEM study, where the
reaction principles are employed to explain that how the metal particles generate and grow at different directions of the
electrode. The current and deformation responses of the samples are measured at the present of a voltage to characterize
the mechano-electrical properties. Then it is concluded that immersing reduction is only suitable as a pre-deposition
process step, and chemical plating is necessary for IPMC with desirable performance.
In this paper, we study the electro-stress in dielectric elastomer (DE) undergoing large deformation
subjected to a high voltage. The electrostriction is investigated and evaluated by the free-energy model
when the dielectric permittivity does not remain constant in actuation. We investigate the nominal and
true electric fields as the DE stretched with the electrostriction involved or not, and the stable domain
for safe actuation is provided.
Dielectric elastomer(DE) could be used in generator design and fabrication, which has been verified by experiments. The
function principle of DE generator is contrary to that of DE actuator. By imposing a low voltage to the dielectric
elastomer membrane, electric charges are accumulated on the two surfaces. Then we apply mechanical force to the sides
of the membrane to produce pre-stretch, and the thickness of the membrane becomes thinner and the capacitance
increases, where mechanical energy is converted to elastic energy. After the mechanical force being withdrawn, because
of elasticity, the thickness of membrane increases while the capacitance decreases, and elastic energy is converted to
electrical energy. This is a work cycle of conversion from elastic to electric energy. Researchers have always been
expecting to find a model that can well predict and evaluate the performance of dielectric elastomer generator. Suo et al.
proposed the typical failure model of neo-Hooken type dielectric elastomer generator and calculates the maximal energy
converted in a mechanical and electrical cycle. In this paper, we demonstrate the area of allowable states of various
Mooney-Rivlin type dielectric elastomer generators, which can be employed to direct the design and fabrication of
Mooney-Rivlin silicone generator, and the results coincide with Suo's theory.
This paper presents a valveless microfluidic chip driven by dielectric elastomers (DEs). First, the planar DE actuator is
designed and the diaphragm actuating performances were characterized. Then the micro chip, containing a pump
chamber and a pair of nozzle/diffuser, is fabricated on SU-8 under exposure to UV-light with a mask. The diaphragm
and the SU-8 is sealed and finally covered by a PMMA. The pumping and flow rate is tested and measured under high
AC supply, and a maxim flow rate of 21.2μl is achieved under 3500V, 8Hz sine wave.