Type Of Electroactive Polymer Research Articles

Real-time actuation of a dielectric elastomer actuator neuroprosthesis for facial paralysis

Facial paralysis is a highly burdening condition, resulting in a patient's inability to move his mimic musculature on one or both sides of his face. This condition compromises the patient's communication and facial expressions, and thus dramatically reduces his quality of life. The current treatment for chronic facial paralysis relies on a complex reconstructive surgery. This publication proposes a novel, less invasive approach for dynamic facial reanimation. The use of a smart material, namely a Dielectric Elastomer Actuator (DEA) is proposed for facial motion restoration, thus avoiding the traditional two-stage free muscle transfer procedure and allowing for a faster recovery of the patient. DEAs are a type of electroactive polymers, showing promising properties similar to natural muscles such as the fact that they are soft, lightweight and allow for large displacements. As a result, a study of the facial muscles and neural interfaces, notably the ones responsible for mouth movement, was performed, in order to implement a realistic setup. In this paper, a non-invasive neural interface based on myoelectric signal is used in order to establish a real-time control of the actuator. Visible motion of a skin model is produced in real time, by synchronizing the actuator to the activity of a healthy muscle, with a maximal delay of 108 ​ms resulting from the signal processing and a delay of less than 30 ​ms related to the actuation of the DEA. This shows that the usage of DEA combined with a neural interface presents a promising approach for treatment of facial paralysis.

Effect of branched structure on microphase separation and electric field induced bending actuation behaviors of poly(urethane–urea) elastomers

Polyurethane elastomers as a type of electroactive polymers have wide applications in soft actuators, soft sensors and energy harvesting due to their high dielectric constant, high electrostriction coefficients, easy processing and structure adjustability, and superior biocompatibility etc. However, the relationship between microstructure and electromechanical properties of EAEs has not been fully understood. In this work, we fabricated the branch structured poly(urethane–urea) elastomers (PUUs) using hydroxy-terminated polybutadiene as soft segment, isophorone diisocyanate and 4,4-diaminodicyclohexylmethane as hard segment, and hydroxyl-terminated four-armed polycaprolactone (PCL410) as branch structured chain extender for improving bending actuation performances, and understanding the relationship between structure and electromechanical properties. The degree of branched structure of PUUs were adjusted by the content of PCL410. The microphase separation kinetics of PUUs was enhanced as increase of PCL410 content, whereas the degree of microphase separation and hard domain size of PUUs were reduced. The mechanical loss and bending actuation stress of PUUs were significantly improved by incorporation of small amount of branched structure into PUU chains. The PUU with 2.60 mol.% of PCL410 showed 5.16 mm of bending displacement and 5.16 Pa of bending actuation stress at 7.2 kV (corresponding to 180 V mm−1 of the nominal electric field), which were 76.3, and 79 times higher than that of PUU without PCL410, respectively. The electric field induced bending actuation mechanism of branch structured PUUs was suggested that the bending actuation mechanism of branch structured PUUs is caused by electrostrictive effect from dipole orientation induced bending deformation of constrained segments and asymmetric charge density distribution on both anode and cathode sides of PUU films. Our results can provide new insight on design novel electroactive polyurethane elastomers.

Shape memory effect and light-induced deformation in Schiff base molecular crystals/PVDF ferroelectric polymer composites

Polyvinylidene difluoride (PVDF)-based polymers have been extensively investigated as a type of electroactive polymer because of their wide applications in flexible sensors, actuators, and transducers. In this work, we demonstrate a new functionality of the PVDF-based polymer-shape memory effect (SME). We show that this effect mainly originates from the ferroelectric-paraelectric phase transition and that shape recovery can be realized at a high speed (<100 ms), superior to most of the existing shape memory polymers. We synthesize modified Schiff base light-sensitive materials and compound them with the polymer to achieve composites exhibiting light-activated SME in the visible light range by exploiting the photothermal effect of the Schiff base compounds. Furthermore, the composites possess light-induced deformation because of the isomerization-induced volume change of the Schiff base molecules under light illumination. To demonstrate the application potential of the multifunctional composites, flexible actuators and robots were designed by combining the thermal-, light-, and electric field-activated SME or deformation. This study not only proposes new multifunctional composites with good application potential, but also presents a new mechanism to design shape memory polymers and expands the functionality of PVDF-based ferroelectric polymers.

Effect of the Particle Size and Layer Thickness of GNP Fillers on the Dielectric Properties and Actuated Strain of GNP-PDMS Composites.

Dielectric elastomer actuators (DEAs), a type of electroactive polymers (EAPs), are smart materials that are used in various fields such as artificial muscles and biomimetic robots. In this study, graphene nanoplatelets (GNPs), which are conductive carbon fillers, were added to a widely used DEA, namely, polydimethylsiloxane (PDMS), to improve its low actuated strain. Four grades of GNPs were used: H5, H25, M5, and M25 (here, the number following the letter indicates the average particle size of the GNPs in μm). The average layer thickness of the H grade is 13–14 nm and that of the M grade is 5–7 nm. PDMS composites were prepared by adding 0.5, 1, 2, and 3 wt% of each GNP, following which the mechanical properties, dielectric properties, and actuated strain of the composites were measured. The mechanical properties were found to increase as the particle size increased. Regarding the dielectric characteristics, it was found that the higher the aspect ratio of the filler, the easier the formation of a micro-capacitor network in the composite—this led to an increase in the dielectric constant. In addition, the higher amounts of GNPs in the composites also led to an increase in the dielectric constant. For the actuated strain analysis, the electromechanical sensitivity was calculated using the ratio of the dielectric constant to the Young’s modulus, which is proportional to the strain. However, it was found that when the loss tangent was high, the performance of the actuated strain decreased owing to the conversion of electric energy into thermal energy and leakage current loss. As a result, the highest actuated strain was exhibited by the M25 composite, with an actuated strain value of 3.01% measured at a low electric field (<4 kV/mm). In conclusion, we proved that the GNP–PDMS composites with a thin layer and large particle size exhibited high deformation.

Modeling the Damage and Self-healing Behaviors of Plasticized PVC Gels

Plasticized polyvinyl chloride (PVC) gel is a type of electroactive polymers, which has potentials to be applied as soft actuators. However, few studies have been performed to investigate the mechanical responses of PVC gels in cyclic loading conditions. In this work, we combined experiments and theory to characterize the mechanical responses of two plasticized PVC gels. The gels were subjected to different types of loading-unloading-reloading cycles. The experimental results showed that the plasticized PVC gels exhibited stress softening response (the Mullins effect) in the cyclic tests. Meanwhile, the gels regained some strength after annealing at room temperature for several hours, indicating the self-healing ability of gels. We further extended the eight-chain model with incorporation of the chain dissociation and reassociation mechanism. The developed constitutive model is able to reproduce the Mullins effect and the recovery of the Mullins effect observed in the experiments. Our results clearly show that understanding the complex mechanical response is crucial for the applications of plasticized PVC gels.

Enhanced Electro-actuation in Dielectric Elastomers: The Nonlinear Effect of Free Ions.

Plasticized poly(vinyl chloride) (PVC) is a jelly-like soft dielectric material that attracted substantial interest recently as a new type of electro-active polymers. Under electric fields of several hundred volt/mm, PVC gels undergo large deformations. These gels can be used as artificial muscles and other soft robotic devices, with striking deformation behavior that is quite different from conventional dielectric elastomers. Here, we present a simple model for the electro-activity of PVC gels and show a nonlinear effect of free ions on its dielectric behaviors. It is found that their particular deformation behavior is due to an electro-wetting effect and to a change in their interfacial tension. In addition, we derive analytical expressions for the surface tension as well as for the apparent dielectric constant of the gel. The theory indicates that the size of the mobile free ions has a crucial role in determining the electro-induced deformation, opening up the way to novel and innovative designs of electro-active gel actuators.

A fractional order model for electrochemical impedance of IPMC actuators based on constant phase element

The accurate modeling of electrical impedance over a wide range of frequency is essential for precise dynamic modeling and control problems of Electroactive Polymer (EAP) actuators. Recently, fractional order modeling has attracted more attention due to the high accuracy. This paper deals with a fractional order electrical impedance model and its identification procedure for a class of EAP actuator named Ionic Polymer Metal Composite (IPMC). To take IPMC’s fractional characteristic into account, constant phase element (CPE) is used to construct a model structure according to Electrochemical Impedance Spectroscopy (EIS). By employing the Levy’s method in combination with genetic optimization algorithm, the unknown parameters of the resulting fractional transfer function are identified. Finally the proposed model is verified, by comparing with experimental EIS data. The results show that the fractional order model has high accuracy for representing the electrical impedance of IPMC actuator. The proposed modeling procedure is general and can also be used for any type of EAPs.

Effect of frequency on dielectric properties of TiO2/PDMS dielectric elastomers

Dielectric elastomeric materials are a new type of electroactive polymers that can produce large deformation under electric field stimulation and can be widely used as actuators and sensors. Among them, Dow Corning’s PDMS is the most widely studied silicone rubber-based dielectric elastomer material. Its key electrical parameters, especially the dielectric constant, affect the overall electromechanical coupling performance. So far, people’s understanding of the dielectric constant value of PDMS dielectric materials is not uniform, especially the influence of frequency on dielectric constant is very different, and few scholars analyze it from the mechanism. Based on this situation, different TiO2/PDMS dielectric elastomers were prepared firstly, and then the influence of frequency (0–105 Hz) on the dielectric properties of TiO2/PDMS dielectric materials was studied by high–low-frequency dielectric constant meter. It is found that the material has strong low frequency dependence and weak high frequency dependence. Finally, from the microscopic point of view, the mechanism of the dielectric constant of TiO2/PDMS dielectric material changing with frequency is due to the fact that material dipole steering polarizability changes with frequency.

Effects of Block Ionomer Morphologies on the Electromechanical Performance of Ionomeric Polymer-Metal Composite Actuators

Ionomeric polymer-metal composites (IPMCs), which is a type of electroactive polymers, can generate a large and fast bending actuation under a low operating voltage (1~5V) (1). This superior electromechanical performance, combined with the inherent nature of polymer such as lightweight and softness, makes them attractive for biomimetic devices such as artificial muscles and soft robots (2). IPMCs have a tri-layer structure that consists of an ionomer film incorporating ions and water (or ionic liquids), and electrodes plated on both film surfaces (1-4). Upon applying a voltage, water and ions move toward the oppositely charged side leading to unsymmetrical polymer swelling. This change is restrained within the polymer’s nonionic matrix resulting in asymmetric stress that drives the bending motion. Advanced electromechanical performance of IPMCs relies on the ion and water transport ability and mechanical integrity of the used ionomer (3-5). In this work, the electromechanical performance of water-based IPMC actuators was examined as a function of the phase-separated morphology of a sulfonated penta-block ionomer (SBI). The SBI films---cast from a range of nonpolar/polar solvent blends---had a series of morphologies varied from poorly-connected ionic domains to well-connected lamellar/hexagonal structures. The poorly-connected structure led to a slow and small actuating response due to the small through-plane ion conductivity (1.5 mS/cm) and water permeability (1.3 × 10-6 mm2/(s MPa)). The SBI film with the lamellar/hexagonal structure however had an excessive water uptake (46wt. %) that greatly impaired the mechanical strength (53 MPa). The IPMC made from this film showed a faster and larger bending over the poorly-connected one but lost the advantage in terms of bending strain energy density. Interestingly, the best-performing IPMC is a SBI film possessing a lamella-like structure with its ionic domains perforated by nonionic polymer matrix. Its superior performance in terms of both bending displacement and strain energy density was attributed to the simultaneous improvements of ion and water transport (19.6 mS/cm and 3.1 × 10-5 mm2/(s MPa), respectively), and mechanical properties (125 MPa). Consequently, an optimal morphology exists for ideal electromechanical performance that is linked to molecule transport and ionomer mechanical properties. (1) Shahinpoor, M.; Kim, K. J. Ionic Polymer – Metal Composites : I .Fundemental. Smart Mater. Struct. 2001, 10, 819-833. (2) Shahinpoor, M.; Kim, K. J. Ionic Polymer–metal Composites: IV. Industrial and Medical Applications. Smart Mater. Struct. 2005, 14 (1), 197–214. (3) Nemat-Nasser, S. Micromechanics of Actuation of Ionic Polymer-Metal Composites. J. Appl. Phys. 2002, 92 (5), 2899–2915. (4) Asaka, K.; Oguro, K. Bending of Polyelectrolyte Membrane Platinum Composites by Electric Stimuli PartII. Response Kinetics. J. Electroanal. Chem. 2000, 480, 186–198. (5) Zhu, Z.; Asaka, K.; Chang, L.; Takagi, K.; Chen, H. Multiphysics of Ionic Polymer–metal Composite Actuator. J. Appl. Phys. 2013, 114 (8), 084902. Figure 1

Electroactive polymers for sensing.

Electromechanical coupling in electroactive polymers (EAPs) has been widely applied for actuation and is also being increasingly investigated for sensing chemical and mechanical stimuli. EAPs are a unique class of materials, with low-moduli high-strain capabilities and the ability to conform to surfaces of different shapes. These features make them attractive for applications such as wearable sensors and interfacing with soft tissues. Here, we review the major types of EAPs and their sensing mechanisms. These are divided into two classes depending on the main type of charge carrier: ionic EAPs (such as conducting polymers and ionic polymer–metal composites) and electronic EAPs (such as dielectric elastomers, liquid-crystal polymers and piezoelectric polymers). This review is intended to serve as an introduction to the mechanisms of these materials and as a first step in material selection for both researchers and designers of flexible/bendable devices, biocompatible sensors or even robotic tactile sensing units.

Approach to the fabrication of acrylic elastomer nanocomposites with high dielectric constants

ABSTRACTDielectric elastomers (DEs) are a type of electroactive polymer that can deform in an electric field. The possession of a high dielectric constant is critical for DEs if they are to be suitable materials for the application of actuators. A novel elastomeric nanocomposite (ACE‐g‐CuPc) was fabricated by copper phthalocyanine oligomer (CuPc) grafting directly onto an acrylic elastomer (ACE) backbone. Compared with other synthetic methods, esterification has several advantages; these include fewer impurities and a simpler synthetic route. Transmission electron microscopy showed that the size of the CuPc particles of the ACE‐g‐CuPc was in the range 15–30 nm; this range was significantly smaller than that of ACE/CuPc (500 nm). The results of thermogravimetric analysis show that the thermal stability of the grafting composite was higher than that of the blending composite. At 100 Hz, the dielectric constant of the grafting composite (with 11 wt % CuPc) reached 173 at room temperature. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43904.

複合型誘電性エラストマーアクチュエータの開発及び特性評価

Dielectric elastomers, as a type of electroactive polymers, have shown great potential for applications. In this study, electromechanical properties of nylon fibers and styrene bars reinforced dielectric elastomer actuators (DEA) are evaluated. As a result the curvature of the styrene bars reinforced DEA is larger than that of the nylon fiber reinforced DEA at a given voltage. Moreover, the time dependence and cyclic dependence of the styrene bars reinforced DEA are investigated and discussed.

유연 복합재료 전극 제조 및 표면조도에 따른 접착 특성에 대한 연구

The fabrication of flexible electrodes coated on the surface of a dielectric elastomer film, which is a type of electroactive polymer (EAP), was carried out. Controlled amounts of Xylitol powder were added (10, 30, 50 and 70 wt%) to the commercial conductive polymer (PEDOT:PSS) to enhance resilience of the electrode. To check resilience of the fabricated composite electrodes, tensile tests were carried out using silicone films coated with the polymer electrodes. From the test results, it was found that 70 wt% Xylitol containing conductive polymer had excellent elongation and high failure strains. Furthermore, surface of the silicone film was uniformly polished with various abrading papers to enhance the wettability of the conductive polymers on the surface of the silicone film. It was found that the silicone film polished with #120 abrading paper had the best wettability and guaranteed excellent bonding behavior.

Active disturbance rejection control for output force creep characteristics of ionic polymer metal composites

Ionic polymer metal composites (IPMCs) are a type of electroactive polymer (EAP) that can be used as both sensors and actuators. An IPMC has enormous potential application in the field of biomimetic robotics, medical devices, and so on. However, an IPMC actuator has a great number of disadvantages, such as creep and time-variation, making it vulnerable to external disturbances. In addition, the complex actuation mechanism makes it difficult to model and the demand of the control algorithm is laborious to implement. In this paper, we obtain a creep model of the IPMC by means of model identification based on the method of creep operator linear superposition. Although the mathematical model is not approximate to the IPMC accurate model, it is accurate enough to be used in MATLAB to prove the control algorithm. A controller based on the active disturbance rejection control (ADRC) method is designed to solve the drawbacks previously given. Because the ADRC controller is separate from the mathematical model of the controlled plant, the control algorithm has the ability to complete disturbance estimation and compensation. Some factors, such as all external disturbances, uncertainty factors, the inaccuracy of the identification model and different kinds of IPMCs, have little effect on controlling the output block force of the IPMC. Furthermore, we use the particle swarm optimization algorithm to adjust ADRC parameters so that the IPMC actuator can approach the desired block force with unknown external disturbances. Simulations and experimental examples validate the effectiveness of the ADRC controller.

Model study of IPMC beam electroactive response based on root deformation

Ionic polymer-metal composite (IPMC) is a type of electroactive polymer (EAP). In this paper, based on Nemat-Nasser model, an improved model is developed to explain the initial nonlinear response of electric actuation on the fixed end deformation. Three IPMC strip samples with different surface resistance are chosen for analysis. Further, from simulation and experiment results, it is found that the root deformation made the tip movement of the IPMC strip with little surface resistance, but this effect was less and less when the surface resistance reduced. The calculation results of this model for the fixed end show a more accurate simulation for the actual deformation of IPMC strips.

Wireless actuation and control of ionic polymer–metal composite actuator using a microwave link

The ionic polymer–metal composite (IPMC), a type of electroactive polymer (EAP) actuator, has created a unique opportunity to design robots that mimic the motion of biological systems due to its soft structure and operation at a low voltage. Although this polymer actuator has strong potential for a next-generation artificial muscle actuator, it has been observed by many researchers that supplying actuation voltages in multiple locations is challenging. In robotic applications, a tethered operation is prohibited and the battery weight can be critical for actual implementation. In this research, the remote unit can provide necessary power and control signals to the target mobile robot units actuated by IPMCs. This research addresses a novel approach of using a wireless power link between the IPMC and a remote unit using microstrip patch antennas designed on the electrode surface of the IPMC for transmitting the power. Frequency modulation of the microwave is proposed to selectively actuate a particular portion of the IPMC where the matching patch antenna pattern is located. This approach can be especially useful for long-term operation of small-scale locomotion units and avoids problems caused by complex internal wiring often observed in various types of biologically inspired robots.

Electrostrictive polymer composite for energy harvesters and actuators

Abstract Polymers have attractive properties when compared with inorganic materials: they are lightweight, inexpensive, pliable, and easily processed and manufactured. They can be configured into complex shapes and their properties can be tailored according to demand. With the rapid advances in materials used in science and technology, various substances embedded with intelligence at the molecular level are being developed. A type of electroactive polymer known as electrostrictive has shown considerable promise for a variety of applications, such as actuation with a strain thickness of 15% for an electric field of 10 V/μm. Polyurethane-based nanocomposite films were prepared by incorporating a carbon black nanopowder (C) into the polymer matrix. Electric field-induced strain measurements revealed that a loading of 1 vt% C (volume percentage of carbon black nanopowder) increased the strain level by a factor of 2.5 at a moderate field strength (10 V/μm). Moreover, another application for this material concerned the harvesting of mechanical energy, which constitutes an attractive alternative to the strict reliance on traditional batteries with limited lifetimes. For instance, an effective conversion from the mechanical-to-electric domains of 2.3 μW/cm3, under a transverse vibration level of 0.25% at 100 Hz, has been demonstrated for nylon. The final results indicated that the dielectric constant was a crucial parameter for energy harvesting.

Modeling and simulation of the coupled mechanical–electrical response of soft solids

Dielectric elastomer (DE) is one type of electro-active polymers (EAP) that responds to electrical stimulation with a significant shape and size change. As EAPs, dielectric elastomers are lightweight, inexpensive, pliable and can be fabricated into various shapes, all of which are attractive properties to justify the intense research in the field. This paper presents a nonlinear, electrical and mechanical coupled, large deformation finite element formulation for DEAs. Maxwell’s equations for the electroquasistatic fields were solved simultaneously with equation of linear momentum. The hyperelastic Ogden model and total Maxwell stress method were combined to describe the material. The formulation was based on the weak forms of Maxwell’s equation and linear momentum expressed in the reference configuration. The closed form consistent tangent moduli for dielectric elastomers were derived. The results of the simulation compared with the experiments have demonstrated the validity of the method from the computational aspect.

A modified self-consistent computational model for an electrostrictive graft elastomer

An electrostrictive graft elastomer, as recently developed by NASA, is a type ofelectro-active polymer. In this paper, a 2D computational model with a self-consistentboundary is developed. Firstly, three-dimensional deformations, induced by both bendingangle and dihedral torsional angle changes, are projected onto a two-dimensional plane.Using both theoretical and numerical analyses, the projected 2D equilibrium bending angleis shown to have the same value as the 3D equilibrium bending angle. The 2D equivalentbending stiffness is derived using a series model based upon the fact that both bending anddihedral torsion produce a configurational change. Equivalent stiffness is justifiedby polymer chain end-to-end distance characteristics. Secondly, a self-consistentscheme is developed to eliminate the boundary effect. Eight images of the unitcell are created peripherally, with the original unit cell in the center. Thus theboundary can only affect the rotation of the eight images, not the central unit cell. Acomputational model is employed to determine the electromechanical properties of theelectrostrictive graft elastomer. Relations between electric field induced strain andelectric field strength are calculated. The effect of molecular scale factors, suchas free volume fraction, graft weight percentage and graft orientation, are alsodiscussed.

Deformation mechanisms of electrostrictive graft elastomer

The electrostrictive graft elastomer is a new type of electroactive polymer. Recentlydeveloped by NASA, it consists of flexible backbone chains, each with side chains, calledgrafts. Neighboring backbone grafts physically cross-link and form crystal units. Theflexible backbone chain and the crystal graft unit consist of polarized monomers, whichcontain atoms with electric partial charges, generating dipole moments. When theelastomer is placed into an electric field, external rotating moments are applied to thedipole moment. This stimulates electrostrictive strain in the graft elastomer. In this paper,the deformation of the elastomer under the action of an electric field is explained by meansof two dominant mechanisms: crystal graft unit rotation and backbone chain reorientation.A two-dimensional computational model is established to analyze the deformation.