High Elastic Energy Density Research Articles

Ultrahigh Elastic Energy Storage in Nanocrystalline Alloys with Martensite Nanodomains.

Elastic materials that store and release elastic energy play pivotal roles in both macro and micro mechanical systems. Uniting high elastic energy density and efficiency is crucial for emerging technologies such as artificial muscles, hopping robots, and unmanned aerial vehicle catapults, yet it remains a significant challenge. Here, a nanocrystalline structure embedded with elliptical martensite nanodomains in ferroelastic alloys wasutilized to enable high yield strength, large recoverable strain, and low energy dissipation simultaneously. As a result, the designed Ti-Ni-V alloys demonstrate ultrahigh energy density (>40 MJ m-3) with ultrahigh efficiency (>93%) and exceptional durability. This concept, which combines nano-sized embryos to minimize energy dissipation of psuedo-elasticity and employs a fine-grained structure to enhance yield strength, can be applied to other ferroelastic materials. Furthermore, it holds promise for the development of phase transformation-involved functionalities such as high-performance dielectric energy storage, ultralow-hysteresis magnetostrain, and high-efficiency solid-state caloriccooling.

Retraction Statement: "High-Volumetric Performance Aligned Nano-Porous Microwave Exfoliated Graphite Oxide-based Electrochemical Capacitors" and "Aligned Nano-Porous Microwave Exfoliated Graphite Oxide Ionic Actuators with High Strain and Elastic Energy Density".

These articles first published on 15 August 2013 and 21 August 2013 on the Wiley Online Library have been retracted at the request of the Research Integrity Officer (RIO) of The Pennsylvania State University, in agreement with the corresponding authors, the journal's Editor-in-Chief, and Wiley-VCH Verlag GmbH & Co. KGaA, because portions of the reported results cannot be considered reliable or reproducible. Following an investigation by the RIO of The Pennsylvania State University, it was found that the data in Figure 2a,b and Figure S1a,b (Supporting Information) of the article with DOI: 10.1002/adma.201301243, and Figure S3 (Supporting Information) of the article with DOI: 10.1002/adma.201301370 were falsified. Data regarding the carbon electrode material, A-aMEGO, reported to have a density of 1.15 g cm-3 , in the article with DOI: 10.1002/adma.201301243, were falsified. The RIO of The Pennsylvania State University confirms that the investigation found that the mentioned data were falsified by the first author. No findings of research misconduct were made against the co-authors of these publications. [1] M. Ghaffari, Y. Zhou, H. Xu, M. Lin, T. Y. Kim, R. S. Ruoff, Q. M. Zhang, Adv. Mater. 25: 2013, 4879. doi:10.1002/adma.201301243 [2] M. Ghaffari, W. Kinsman, Y. Zhou, S. Murali, Q. Burlingame, M. Lin, R. S. Ruoff, Q. M. Zhang, Adv. Mater. 25: 2013, 6277. doi:10.1002/adma.201301370.

Active membrane-based silencer and its acoustic characteristics

Abstract A membrane-based silencer using dielectric elastomer absorbers (DEAs) was developed and explored in the present study. Dielectric elastomer, a soft smart material, was used to fabricate this actuator. It has the characteristic of lightweight, high elastic energy density and large deformation under external direct current (DC) or alternating current (AC) voltages. The typical acoustic performances of this membrane-based silencer were experimentally identified using a transmission loss (TL) duct acoustic measurement system. It was found that the resonance peaks of this membrane-based silencer could be controlled by applying different external voltages, a maximum resonance frequency shift of 59.5 Hz for the resonance peaks was achieved which indicated that this membrane-based silencer could be adjusted to absorb the target noise without any addition mechanical part. Furthermore, the resonance shift and multiple resonances mechanisms using DEAs were proposed and discussed which was aiming to achieve multi-peaks noise reduction. The present results also provide insight into the appropriateness of the absorber for possible use as an acoustic treatment to replace the traditional acoustic treatment in the noise reduction technology.

An electronically tunable duct silencer using dielectric elastomer actuators.

A duct silencer with tunable acoustic characteristics is presented in this paper. Dielectric elastomer, a smart material with lightweight, high elastic energy density and large deformation under high direct current/alternating current voltages, was used to fabricate this duct silencer. The acoustic performances and tunable mechanisms of this duct silencer were experimentally investigated. It was found that all the resonance peaks of this duct silencer could be adjusted using external control signals without any additional mechanical part. The physics of the tunable mechanism is further discussed based on the electro-mechanical interactions using finite element analysis. The present promising results also provide insight into the appropriateness of the duct silencer for possible use as next generation acoustic treatment device to replace the traditional acoustic treatment.

Electric field induced variation of temperature and entropy in dielectric elastomers

Dielectric elastomer is a kind of typical electro-active polymer material. Under external electric field it can produce large electrostriction deformation and possesses the advantages of high elastic energy density, super short response time, high efficiency, and so on. It is widely used in the artificial muscles, facial expressions, actuators, energy harvesters, sensors, robots and Braille display devices, and also shows huge application potential in the aerospace and intelligent bionic areas. We built the free energy of the dielectric elastomer electrical-mechanical coupling system and investigated its constitutive relation and stability behavior. Then we calculated the elastomer’s critical deformation suffering from the voltage. If electrical breakdown, electromechanical instability and snap-through instability can be avoided, the large electrostriction deformation can induce adiabatic temperature change and isothermal entropy change of the dielectric elastomer. We used the entropy-temperature or electric displacement-electric field plane to describe the temperature change and entropy change of dielectric elastomer undergoing large electrostriction deformation. With the influence of temperature, we developed a temperature and deformation coupling thermodynamical free energy model to calculate the electric field induced variation of temperature and entropy in dielectric elastomers. The results should offer great help in guiding the design and fabrication of excellent actuators featuring soft dielectric elastomers.

High electromechanical reponses of ultra-high-density aligned nano-porous microwave exfoliated graphite oxide/polymer nano-composites ionic actuators

High elastic energy density and high-efficiency ionic electromechanical actuators were prepared from aligned activated microwave exfoliated graphite oxide (A-aMEGO)/polymer nano-composites, and the electromechanical performance was characterized. The elastic modulus and elastic energy density of the ionic actuators can be tuned over a wide range by varying the polymer (poly (vinylidene fluoride/chlorotrifluoroethylene) [P(VDF-CTFE)]) concentration in the nano-composite actuators. The A-aMEGO/P(VDF-CTFE) nano-composite actuators with 35 wt.% of polymer content exhibit an elastic energy density higher than 5 J/cm3 and an electromechanical conversion efficiency higher than 3.5%, induced under 4 V. The results show the promise of high-density highly aligned graphene electrodes for high-performance ionic electromechanical transduction devices.

Acoustic characteristics of a dielectric elastomer absorber

The present paper is devoted to study the acoustic characteristics of a dielectric elastomer (DE) absorber, which has a wide variety of potential applications as a novel actuator technology. DE, a lightweight and high elastic energy density smart material, can produce a large deformation under high DC/AC voltages. These excellent characteristics can be used to improve the present typical noise control systems. The performance of using this new soft-controlled-material is experimentally investigated. It is found that the voltage on the DE could tune the resonance frequencies of DE absorber thus it could absorb broadband noise. The results also provide insight into the appropriateness of the absorber for possible use as an active noise control system for replacing the traditional acoustic treatment.

Aligned Nano‐Porous Microwave Exfoliated Graphite Oxide Ionic Actuators with High Strain and Elastic Energy Density

A high-density aligned nanoporous activated microwave exfoliated graphite oxide (aMEGO) ionic actuator is studied. Before applying an external electric field, the cations and anions are randomly distributed in the composite. After applying the electric field, ions ingress in between the aligned aMEGO sheets through the nanopores to compensate the charges on the electrodes, resulting in the separation of neighboring sheets and unidirectional electro actuation.

An active energy harvesting scheme with an electroactive polymer

We investigate the energy harvesting with an electrostrictive polymer, possessing high electromechanical response and elastic energy density, which make it possible to generate high electric energy density and attractive for the active energy harvesting scheme. It is shown that combining the active energy harvesting scheme and high electromechanical response of the polymer yields a harvested electric energy density of ∼40mJ∕cm3 with a 10% efficiency.

Interpenetrating networks of elastomers exhibiting 300% electrically-induced areastrain

Mechanical prestrain is generally required for most electroelastomers to obtain highelectromechanical strain and high elastic energy density. However, prestrain cancause several serious problems, including a large performance gap between theactive materials and packaged actuators, instability at interfaces between theelastomer and prestrain-supporting structure, and stress relaxation. Difunctional andtrifunctional liquid additives were introduced into 400% biaxially prestrained acrylicfilms and subsequently cured to form the second elastomeric network. The goal ofthis research was to determine the effect of different functional additives andconcentrations on the microstructure, the mechanical properties, and the actuation ofcomposite films. In the as-obtained interpenetrating polymer networks (IPNs), theadditive network can effectively support the prestrain of the acrylic films and as aresult, eliminate the external prestrain-supporting structure. However, the largeamount of additive used to completely preserve prestrain was found to makethe films too stiff, causing damage to IPN composite films. Furthermore, theinterpenetrating network formed from a trifunctional monomer is more effective than thatformed from a difunctional monomer in supporting the high tension of the VHBnetwork. This high efficiency trifunctional additive leads to the enhancement of thebreakdown field, due to less damage on the microstructure. The IPN compositefilms without external prestrain exhibit electrically-induced strains up to 300% inarea, comparable to those of VHB 4910 films under high prestrain conditions.

Electroactive polymer based microfluidic pump

A planar, valveless, microfluidic pump using electrostrictive poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] based polymer as the actuator material is presented. P(VDF-TrFE) thick films having a large electrostrictive strain ∼5–7% and high elastic energy density of 1 J/cm 3 have been used in a unimorph diaphragm actuator configuration. The microfluidic pump was realized by integrating a nozzle/diffuser type fluidic mechanical-diode structure with the polymer microactuator. The P(VDF-TrFE) unimorph diaphragm actuator, 80 μm thick and 2.2 mm × 2.2 mm in lateral dimensions, showed an actuation deflection of 80 μm for an applied electric field of 90 MV/m. The microfluidic pump could pump methanol at a flow rate of 25 μl/min at 63 Hz with a backpressure of 350 Pa. The flow rate of this pump could be easily controlled by external electrical field. Two different sizes of nozzle/diffuser elements were studied and the pumping efficiency of these structures is 11 and 16%, respectively.

A theoretical analysis of experimental results of shock wave loading of OFE copper relating the observed internal structure to the deformation mechanism

The observations made by Gray and Follansbee of the internal metallurgical changes in oxygen-free electrolytic copper specimens that were subjected to sharply terminated shock loadings of 5, 10 and 20 GPa led to conclusions about the mechanisms of shock loading and its pressure release that may be helpful in formulating the material constitutive equation. Details of the shock load mechanism obtained from these experiments may explain the micro-structure observations made and provide quantitative details for modeling of this important transient process. It was particularly noticed that micro-structural changes caused by the shock front passage through the specimen resulted in a time period after the shock front arrival, called the temporary retardation time, when the material elastic load could not be released by plastic deformation involving internal shearing. This temporary retardation time makes the accumulation of high elastic energy density at high strain rates possible. The accumulated elastic energy may possibly be discharged via shear bands’ formation although occurring of other failure modes of the material cannot be excluded. Formulation is suggested for incorporating the retardation time into material models suitable for hydrocodes.

An Investigation of Energy Harvesting Using Electrostrictive Polymers

ABSTRACTOwing to their low acoustic impedance, high elastic energy density, and relatively high electromechanical conversion efficiency, the electroactive polymers have begun to show the potential for energy harvesting or mechanical to electrical energy conversion. In addition, due to the electromechanical coupling in these materials the electric and mechanical properties of these polymers will depend on the imposed electrical and mechanical conditions. This paper discusses how to utilizing this unique property to maximum the energy conversion efficiency and the harvested electrical energy density in the electrostrictive polymers. As an example, we demonstrate that when a properly phased and externally applied electric AC field is superimposed on the mechanical cycle, an output electrical energy density of 39mJ/cm3 and mechanical-to-electrical conversion efficiency of about 10% can be obtained from the electrostrictive P(VDF-TrFE) based polymers.

Poly(vinylidene fluoride-trifluoroethylene) based high performance electroactive polymers

Making use of defects modification to P(VDF-TrFE) via either high energy electron irradiation treatment or copolymerizing VDF-TrFE with a small amount of chlorinated monomer to form a random terpolymer, we demonstrate that high electromechanical responses can be realized in P(VDF-TrFE) based polymers. It will be shown that in the stretched and irradiated 68/32 mol% copolymer, a transverse strain of 4.5% and a transverse electromechanical coupling factor k/sub 31/ of 0.65 can be induced under a field of 85 MV/m. In addition, the irradiated copolymer also exhibits a high elastic energy density, /spl sim/ 1 J/cm/sup 3/. For PVDF based terpolymers such as P(VDF-TrFE-CFE) terpolymer (CFE: chlorofluoroethylene), an electrostrictive strain of more than 7% can be obtained. To elucidate the microstructure changes due to the defects modification in P(VDF-TrFE) based polymers, synchrotron X-ray measurement was carried out on the irradiated copolymers and the results show that, the irradiation converts the polar-phase into a nonpolar phase. In addition, X-ray date show that the polar-phase can be induced, at the expense of the nonpolar phase, by external fields, confirming that the field induced conformation change is responsible for the observed high electromechanical responses. Although the modified PVDF based polymer exhibits the highest room temperature dielectric constant (60 versus below 10), it is still far below those in the inorganic materials. Experimental results show that by using delocalized electrons in conjugated bonds an all-organic composite with a dielectric constant more than 400 can be achieved. As a result, a strain of near 2% with an elastic energy density higher than 0.1 J/cm/sup 3/ can be induced under a low applied field of 13 V//spl mu/m. The strain is proportional to the applied field and the composite has an elastic modulus near 1 GPa.

High-Dielectric-Constant All-Organic/Polymeric Composite Actuator Materials

ABSTRACTAmong various electroactive polymer (EAP) actuator materials developed recently, the class of EAPs whose responses are stimulated by external electrical fields (often known as the field type EAPs) is especially attractive due to their high strain level and elastic energy density. However, for most field type EAPs, dielectric constant is low, generally less than 10. Consequently, these polymers usually require high electric fields (>100 V/μm) to generate high elastic energy density which limits their applications. In this paper, we will investigate some avenues to significantly raise the dielectric constant and electromechanical response in field type polymeric materials. By exploiting an all-organic composite approach in which high-dielectric-constant organic particulates were blended with a polymer matrix, a polymeric-like material can reach a dielectric constant higher than 400, which results in a significant reduction of the applied field to generate high strain with high elastic energy density. An all-polymer high-dielectric-constant (K>1,000 @1 kHz) percolative composite material was fabricated by the combination of conductive polyaniline particles (K>105) within a fluoroterpolymer matrix (K>50). These high-K polymer hybrid materials also exhibit high electromechanical responses under low applied fields. In addition, a three-component all-organic composite was designed and prepared to improve the dielectric constant and the electromechanical response, as well as the stability of the composites, in which a high-dielectric-constant organic dielectric phase and an organic conductive phase were embedded into the soft dielectric elastomer matrix.

Design, fabrication, and performance of a flextensional transducer based on electrostrictive polyvinylidene fluoride-trifluoroethylene copolymer.

Taking advantage of the high electrostrictive strain and high elastic energy density of a newly developed electrostrictive polymer, modified poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] based polymers, a flex-tensional transducer was designed, and its performance was investigated. The flextensional transducer consists of a multilayer stack made of electrostrictive P(VDF-TrFE) polymer films and two flextensional shells fixed at the ends to the multilayer stack. Because of the large transverse strain level achievable in the electrostrictive polymer and the displacement amplification of the flextensional shells, a device of a few millimeters thick and lateral dimension about 30 mm x 25 mm can generate an axial displacement output of more than 1 mm. The unique flextensional configuration and the high elastic energy density of the active polymer also enable the device to offer high-load capability. As an underwater transducer, the device can be operated at frequencies below 1 kHz and still exhibit relatively high transmitting voltage response (TVR), very high source level (SL), and low mechanical quality factor (Qm).

High-performance micromachined unimorph actuators based on electrostrictive poly(vinylidene fluoride–trifluoroethylene) copolymer

We report on the performance of micromachined unimorph actuators [(polymer micromachined actuator PMAT)] based on the electrostrictive poly(vinylidene fluoride–trifluoroethylene) [P(VDF–TrFE)] copolymer. Because of the high electrostrictive strain and high elastic energy density (∼1 J/cm3) of the active polymer [the electrostrictive P(VDF–TrFE)], the PMAT exhibits a very high stroke level with high load capability and high displacement voltage ratio. In addition, the experimental data also demonstrate that the PMAT is capable of operating over a broad frequency range (>100 kHz). The PMAT performance was modeled and the agreement between the modeling results and experimental data confirms that the response of the PMAT indeed follows the design parameters.

Investigation of Polymer Micro-Actuators Based on Electrostrictive Poly(vinylidene fluoride-trifluoroethylene) Copolymers

ABSTRACTMicromachined actuators based on the electrostrictive P(VDF-TrFE) copolymer, which possesses a high strain (∼5%) and high elastic energy density (∼ 1 J/cm3), have been designed and fabricated. The performance of the devices have been characterized and modeled in terms of the properties of the copolymer and dimensions of the devices. The experimental results on the device responses under high AC fields (electrostrictive mode), weak AC fields in DC field biased state, and frequency dependence, are very close to the modeling results. Due to the large field induced strain and high frequency capability of the electrostrictive P(VDF-TrFE), the device possesses the capability of operation at non-resonance mode with high displacement and force output, and hence, the device is capable to be used over a broad frequency range. For example, for a device of 1 mm lateral dimension, the displacement output can reach more than 50 μm and the ratio of the displacement/applied voltage is more than 20 nm/Vrms. Furthermore, over more than 3 frequency decades (up to 100 kHz), the dispersion of the displacement is less than 20%. The observed performance of the devices indicates that this class of the electrostrictive P(VDF-TrFE) based micro-actuators is attractive for micropumps and valves.

Electrostrictive poly(vinylidene fluoride-trifluoroethylene) copolymers

High energy electron (1.0–2.55 MeV) irradiation was used to modify the phase transitional behavior of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymers in an attempt to significantly improve the electromechanical properties of the copolymers. It is found that the copolymers under a proper irradiation treatment exhibit very little room temperature polarization hysteresis and very large electrostrictive strain (the longitudinal strain of −5% can be achieved). Because of the large anisotropy in the strain responses along and perpendicular to the polymer chain, the transverse strain can be tuned over a broad range by varying the film stretching condition. For unstretched films, the magnitude of transverse strain is approximately about/less than 1/3 of that of the longitudinal strain, and for stretched films, the transverse strain along the stretching direction is comparable to the longitudinal strain. In addition to the high strain response, the irradiated copolymers also possess high elastic energy density and mechanical load capability as indicated by the relatively high elastic modulus of the copolymer and the high strain response of the transverse strain even under 40 MPa tensile stress. The high strain and high elastic modulus of the irradiated copolymer also result in an improved electromechanical coupling factor where the transverse coupling factor of 0.45 has been observed. The frequency dependence of the strain response was also characterized up to near 100 kHz and the results show that the high electromechanical response can be maintained to high frequencies. Several unimorph actuators were fabricated using the modified copolymer and the test results demonstrate high performance of the devices due to the high strain and high load capability of the material.

Relaxor ferroelectric behavior in high-energy electron-irradiated poly(vinylidene fluoride-trifluoroethylene) copolymers

This paper presents experimental results showing that in a certain composition range and under a proper electron-irradiation treatment, a normal ferroelectric poly(vinylidene fluoride-trifluoroethylene) copolymer can be converted into a material exhibiting many typical features of relaxor ferroelectrics, suggesting that this is a new class of relaxor ferroelectric material. Furthermore, the irradiated copolymer can generate giant electrostriction (≈5%) with a high elastic energy density. The X-ray diffraction results obtained from the irradiated copolymer under electric field, indicate that the observed polarization and strain responses are mainly due to the local phase transformation from a non-polar phase to a polar phase.