Electroactive Polymer Composites Research Articles

Electroactive performance and cost evaluation of carbon nanotubes and carbon black as conductive fillers in self-healing shape memory polymers and other composites

Multiwalled carbon nanotubes (MWCNT) and carbon black (CB) have been widely used as conductive fillers in electroactive polymer composites. MWCNT-based composites generally have lower resistivity and percolation thresholds, while CB-based ones are considerably cheaper. To balance these pros and cons, ternary composites (TCs) (polymer-MWCNT-CB) can be formulated. Here, we prepared electroactive MWCNT-CB TCs capable of self-healing and with shape memory properties, based on polyketones reversibly-crosslinked via Diels-Alder chemistry. Unexpectedly, the cheaper CB-rich formulations had lower resistivities, thus better electroactive self-healing and shape memory responses. Nonetheless, not all electroactive MWCNT-CB TCs have this clear cost-effectiveness. We evaluated the cost-performance of multiple reported MWCNT-CB TCs systems and found different general trends (positive, negative, and synergistic cost-efficiency relationships). Thus, the cost-effectiveness of these fillers (and their combination) greatly depends on each composite system and what it is intended for. This work includes the first systematic report on cost-performance of MWCNT and CB as conductive fillers.

Programmable morphing, electroactive porous shape memory polymer composites with battery-voltage Joule heating stimulated recovery

Direct fabrication of electroactive shape memory polymer composites (eSMPCs) into complex non-planar geometries is highly desirable to enable remotely deployable, form-functional structures. However, traditional processes such as injection molding, casting, and extrusion limit the producible geometries to planar ribbons, wires, or tubes and the design of deployment modes to flattening-out/self-folding motions. To achieve low-voltage eSMPCs with a complex geometry, we report a direct fabrication strategy of bespoked-geometry eSMPCs via a two-stage sequential cure-and-foam technique for a new type of porous eSMPC, functionalized with 3D graphene nanofoam monolith (3DC). In our method, we resolved the difficulty in shaping fragile 3DC, and thus, various complex shape transforms (curved, helical, and wavy) can be intuitively designed via direct sculpting. Our method can be compatible with kirigami techniques for the design of hierarchical and combinatorial shape-change structures. 3DC not only serves as an intrinsic heater but, during synthesis, its cell walls also act as a confinement framework for architecting porosity within 3DC-eSMPCs, which can be actuated with low-voltage (7.5 V, <2 W). The herein reported 3DC-eSMPC and its synthesis strategy represent a new method and material to fabricate low-voltage deployables of bespoked shapes, capable of low-voltage actuation.

Viscoelastic up-scaling rank-one effects in in-silico modelling of electro-active polymers

This paper analyses the viscoelastic up-scaling effects in electro-active polymers endowed with a micro-structure architecture in the form of a rank-one laminate. The principles of rank-n homogenisation and thermodynamical consistency are combined in the context of extremely deformable dielectric elastomers actuated well beyond the onset of geometrical instabilities. To ensure the robustness of the resulting methodology, Convex Multi-Variable (CMV) energy density functionals enriched with a nonlinear continuum viscoelastic description are used to describe the physics of the individual microscopic constituents. The high nonlinearity of the visco-electro-mechanical problem is resolved via a monolithic multi-scale Newton–Raphson scheme with a Backward-Euler (implicit) time integration scheme. A tensor cross product operation between vectors and tensors and an additive decomposition of the micro-scale deformation gradient (in terms of macro-scale and fluctuation components) are used to considerably reduce the complexity of the algebra. The resulting computational framework permits to explore the time-dependent in-silico analysis of rank-one electro-active polymer composites exhibiting extremely complex deformation patterns, paying particular attention to viscoelastic up-scaling effects. A comprehensive series of numerical examples is presented, where specially revealing conclusions about the rate-dependency of the composite electro-active polymer are observed as a function of its microstructure orientation and viscoelastic content. In a rectangular film subjected to extreme bending deformation, two different deformation modes are observed with one prevailing mode depending on the laminate composition. For the case of a square membrane where extreme deformation induces buckling, it is shown that the viscoelastic contribution leads to larger values of (stable) deformation, due to the regularisation that viscoelasticity inherently provides.

Electroactive Self-Healing Shape Memory Polymer Composites Based on Diels–Alder Chemistry

Both shape memory and self-healing polymers have received significant attention from the materials science community. The former, for their application as actuators, self-deployable structures, and medical devices; and the latter, for extending the lifetime of polymeric products. Both effects can be stimulated by heat, which makes resistive heating a practical approach to trigger these effects. Here we show a conductive polyketone polymer and carbon nanotube composite with cross-links based on the thermo-reversible furan/maleimide Diels–Alder chemistry. This approach resulted in products with efficient electroactive shape memory effect, shape reprogrammability, and self-healing. They exhibit electroactive shape memory behavior with recovery ratios of about 0.9; requiring less than a minute for shape recovery; electroactive self-healing behavior able to repair microcracks and almost fully recover their mechanical properties; requiring a voltage in the order of tens of volts for both shape memory and self-healing effects. To the best of our knowledge, this is the first report of electroactive self-healing shape memory polymer composites that use covalent reversible Diels–Alder linkages, which yield robust solvent-resistant polymer networks without jeopardizing their reprocessability. These responsive polymers may be ideal for soft robotics and actuators. They are also a step toward sustainable materials by allowing an increased lifetime of use and reprocessability.

Development of ionic liquid-based electroactive polymer composites using nanotechnology

Abstract This review is intended to provide an overview of the design and fabrication of ionic liquid-based ionic electroactive polymer (IL-iEAP) transducers for advanced applications in biological and electronic fields. The iEAP is a class of smart materials that can perform sensing or actuating functions by controlling the movement of cations and anions in the active layer. This type of material can deform under low voltage stimulation and generate electrical signals when undergoing mechanical deformation because of ion redistribution. Numerous research attention has been focused on studying the deformation mechanisms and the potential for actuation, sensing, and energy harvesting applications. Compared to the traditional water-based iEAP, the non-volatile IL-iEAP delivers a wider electrochemical window and a more stable actuation performance. In this paper, the classification of iEAP with different actuation mechanisms is first outlined, followed by introducing various preparation methods including nanotechnology for IL-iEAPs, and discussing the key factors governing their actuation performance. In addition, the advanced functions of IL-iEAP in actuating and sensing, especially self-sensing in bionics and electromechanical equipment applications, are reviewed. Finally, novel nanotechnologies used for fabricating IL-iEAPs and the prospects of their microelectromechanical system (MEMS) applications are discussed.

A 3D analytical ion transport model for ionic polymer metal composite actuators in large bending deformations

Ionic polymer metal composites (IPMCs) are a kind of soft electroactive polymer composites. An IPMC strip commonly has a thin polymer membrane coated with a noble metal as electrodes on both sides. Whenever an electric voltage is applied to the IPMC, it bends and whenever it is deformed, a low voltage is measurable between its electrodes, hence IPMC is an actuator as well as a sensor. They are well known for their promising features like low density, lightness, high toughness and remarkable stimulus strain, also, they have the potential for low-voltage operation while exhibiting acceptable large bending deformation. In this paper, a three-dimensional (3D), dynamic and physics-based model is presented analytically and experimentally for IPMC actuators. The model combines the ion transport dynamics within the IPMC and the bending dynamics of it as a beam under an electrical stimulation. In particular, we present an analytical model to create a relation between the input voltage and the output tip displacement of an IPMC actuator for large bending deformations. Experimental results show that the proposed model captures well the tip displacement.

A Convex Multi-Variable based computational framework for multilayered electro-active polymers

This paper presents a novel computational framework for the in silico analysis of rank-one multilayered electro-active polymer composites exhibiting complex deformation patterns. The work applies the principles of rank-n homogenisation in the context of extremely deformable dielectric elastomers actuated beyond the onset of geometrical instabilities. Following previous work by the authors (Gil and Ortigosa, 2016; Ortigosa and Gil, 2016; Ortigosa and Gil, 2016) Convex Multi-Variable (CMV) energy density functionals are used to describe the physics of the individual microscopic constituents, which is shown to guarantee ab initio the existence of solutions for the microstructure problem, described in terms of the so-called deformation gradient and electric displacement amplitude vectors. The high nonlinearity of the quasi-static electro-mechanical problem is resolved via a monolithic multi-scale Newton–Raphson scheme, which is enhanced with a tailor-made arc length technique, used to circumvent the onset of geometrical instabilities. A tensor cross product operation between vectors and tensors and an additive decomposition of the micro-scale deformation gradient (in terms of macro-scale and fluctuation components) are used to considerably reduce the complexity of the algebra. The possible loss of ellipticity of the homogenised constitutive model is strictly monitored through the minors of the homogenised acoustic tensor. A series of numerical examples is presented in order to demonstrate the effect that the volume fraction, the contrast and the material properties, as well as the level of deformation and electric field, have upon the response of the composites when subjected to large three dimensional stretching, bending and torsion, including the possible development of wrinkling.

Property of Nafion-ionic polymer-metal composites based on Mori–Tanaka methodology and gradient mechanics

Ionic polymer-metal composite (IPMC) actuators are a class of electroactive polymer composites that exhibit some interesting electromechanical characteristics such as low voltage actuation, large displacements, and benefit from low density and elastic modulus. Elastic modulus and surface resistance are basic properties of IPMCs that play a role in almost all practical applications of these materials. The prediction of the elastic modulus and surface resistance is of extreme importance to better grasp the mechanical behavior of IPMCs and to evaluate the success of the design. This paper has proposed a theoretical framework for predicting the elastic modulus and surface resistance of copper electrodes IPMCs. A five layers analytical assemblage model is introduced for the IPMCs relied upon improved classical lamination theory. The depositional metallic atoms were used as the exterior layer, the ionic polymer was used as the middle layer, and the material between the two layers was a gradient layer. Based on Mori–Tanaka methodology and gradient mechanics, the overall elastic properties of composites are obtained and lie between those obtained from the experiment. The prediction showed a good agreement with the experimental elastic modulus values with a maximum deviation of less than 10%. The overall results have provided useful insight into the elastic modulus and surface resistance effects to the properties of the IPMC. This would open further opportunities toward the higher application of IPMC.

Ionic-Liquid-Based Electroactive Polymer Composites for Muscle Tissue Engineering

As an electromechanically active tissue, muscle regeneration takes advantage of active scaffolds providing mechanoelectrical stimuli and a biomimetic microenvironment. Thus, this study reports on t...

Computational stability analysis of periodic electroactive polymer composites across scales

This paper is devoted to the multiscale stability analysis of periodic electroactive polymer composites at finite deformations. A particular focus is on the investigation of macroscopic loss of strong ellipticity and microscopic bifurcation-type instabilities. Macroscopic homogenized quantities are determined by use of computational homogenization over selected representative volume elements (RVE). The quasi-incompressible nature of the electroactive polymers is taken into account by considering a four-field variational formulation at micro-level. This formulation includes continuous interpolations of displacement fields and electric vector potentials as well as discontinuous interpolations of pressure and dilatation terms, yielding a saddle-point principle for coupled problems. Static condensation of the terms related to the element-wise constant pressure and dilatation results in a positive definite global microscopic stiffness matrix until a microscopic instability occurs. The microstructure is embedded into a macroscopic driving procedure that imposes periodic mechanical and electrical boundary conditions on the surface of the RVEs. It is known that at certain finite deformations the initial periodicity of microstructures might be altered due to microscopic bifurcation-type instabilities. To incorporate microscopic instabilities and to determine the critical periodicity of microstructures, Bloch–Floquet wave analysis in the context of a finite element discretization is implemented. The macroscopic instabilities, which are related to the long-wavelength microscopic instabilities, are determined by checking the loss of strong ellipticity at macro-scale. The proposed setting is used to study the multiscale stability analysis of electroactive polymer composites with embedded fibers. The influence of fiber volume fraction and aspect ratio of fiber cross sections on instabilities are investigated in detail. Critical periodicities and bifurcation modes are demonstrated for selected boundary value problems.

Computational Multi‐Scale Stability Analysis of Periodic Electroactive Polymer Composites at Finite Strains

AbstractThis work is dedicated to multi‐scale stability analysis, especially macroscopic and microscopic stability analysis of periodic electroactive polymer (EAP) composites with embedded fibers. Computational homogenization is considered to determine the response of materials at macro‐scale depending on the selected representative volume element (RVE) at micro‐scale [4, 5]. The quasi‐incompressibility condition is considered by implementing a four‐field variational formulation on the RVE, see [7]. Based on the works [1–3, 6, 8] the macroscopic instabilities are determined by the loss of strong ellipticity of homogenized moduli. On the other hand, the bifurcation type microscopic instabilities are treated exploiting the Bloch‐Floquet wave analysis in context of finite element discretization, which allows to detect the changed critical size of periodicity of the microstructure and critical macroscopic loading points. Finally, representative numerical examples are given which demonstrate the onset of instability surfaces, the stable macroscopic loading ranges, and further a periodic buckling mode at a microscopic instability point is presented. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Selective localization of multi-walled carbon nanotubes in bi-component biodegradable polyester blend for rapid electroactive shape memory performance

In this study, we reported a rapid electroactive ternary shape memory polymer (SMP) composites containing multiwalled carbon nanotubes (MWCNTs) and two biodegradable polyesters, namely poly(propylene carbonate) (PPC) and poly(lactic acid) (PLA). To do this, binary polymer blends were firstly prepared, and a good shape memory behavior was observed for blends with co-continuous phase morphology, where by PPC acted as the switching domain due to its good elasticity and PLA acted as the fixing domain due to its high modulus. Then MWCNTs were incorporated into PPC/PLA co-continuous phase (PPC70/PLA30, PPC50/PLA50) by simple melting blending to realize the electroactive shape memory properties. It was found that MWCNTs tended to locate more in the PPC phase than in the PLA phase. The selective localization of MWCNTs not only led to an improvement in the recovery force, but also imparted composites with high electrical conductivity in a low percolation threshold. The composites showed rapid electroactive shape memory behavior, which reached a shape recovery ratio of 97% within 30 s at 30 V. Our work provides a simple approach to utilize the selective localization of MWCNTs in the continuous phase to fabricate rapid electrical actuated SMPs with low MWCNTs loadings, which can be scaled up industrially.

Silicone Membranes to Inhibit Water Uptake into Thermoset Polyurethane Shape-Memory Polymer Conductive Composites.

Electroactive shape memory polymer (SMP) composites capable of shape actuation via resistive heating are of interest for various biomedical applications. However, water uptake into SMPs will produce a depression of the glass transition temperature (Tg ) resulting in shape recovery in vivo. While water actuated shape recovery may be useful, it is foreseen to be undesirable during early periods of surgical placement into the body. Silicone membranes have been previously reported to prevent release of conductive filler from an electroactive polymer composite in vivo. In this study, a silicone membrane was used to inhibit water uptake into a thermoset SMP composite containing conductive filler. Thermoset polyurethane (PU) SMPs were loaded with either 5 wt% carbon black (CB) or 5 wt% carbon nanotubes (CNT) and subsequently coated with either an Al2O3- or silica-filled silicone membrane. It was observed that the silicone membranes, particularly the silica-filled membrane, reduced the rate of water absorption (37 °C) and subsequent Tg depression versus uncoated composites. In turn, this led to a reduction in the rate of recovery of the permanent shape when exposed to water at 37 °C.

Nonlinear dynamic modeling of ionic polymer conductive network composite actuators using rigid finite element method

Ionic polymer conductive network composite (IPCNC) actuators are a class of electroactive polymer composites that exhibit some interesting electromechanical characteristics such as low voltage actuation, large displacements, and benefit from low density and elastic modulus. Thus, these emerging materials have potential applications in biomimetic and biomedical devices. Whereas significant efforts have been directed toward the development of IPMC actuators, the establishment of a proper mathematical model that could effectively predict the actuators’ dynamic behavior is still a key challenge. This paper presents development of an effective modeling strategy for dynamic analysis of IPCNC actuators undergoing large bending deformations. The proposed model is composed of two parts, namely electrical and mechanical dynamic models. The electrical model describes the actuator as a resistive-capacitive (RC) transmission line, whereas the mechanical model describes the actuator as a system of rigid links connected by spring-damping elements. The proposed modeling approach is validated by experimental data, and the results are discussed.

Dielectric elastomer composites: small-deformation theory and applications

We provide estimates for the effective response of Electro-Active Polymer Composites (EAPCs) consisting of aligned ellipsoidal inclusions of a stiff dielectric material which are distributed randomly in an soft elastomeric matrix with “ellipsoidal” two-point statistics. The derivation of the results for the electro-mechanical response assumes linearized deformations, but includes non-linear (quadratic) terms in the electric fields. We investigate three different physical mechanisms contributing to the macroscopic electro-mechanical response of the composite: the intrinsic effect of the particles on the Maxwell stress, the inter-particle (dipole) interactions which are accounted for by evaluating the effect of changes in the “shape” of the two-point probability functions with the deformation, and the effect of particle rotations and torques when the geometric and/or anisotropy axis of the particles are not aligned with the applied electric field. Several illustrative examples are provided to emphasize the relative importance of the different effects on the overall electrostriction of the composites. In particular, for the “compliant electrode” boundary conditions that are widely used in applications, it is shown that inter-particle interactions are synergistic with the intrinsic effect of the particles on the Maxwell stress, leading to significant enhancements in the electro-mechanical coupling of the EAPCs, especially at high particle concentrations. On the other hand, the effect of electric torques on non-aligned particles is generally deleterious for electrostriction.

Electrorotation of novel electroactive polymer composites in uniform DC and AC electric fields

Novel electroactive polymer composites have been developed that could spin in uniform DC and AC electric fields. The angular displacement as well as rotation of polymer disks around an axis that is perpendicular to the direction of the applied electric field was studied. It was found that the dynamics of the polymer rotor is very complex. Depending on the strength of the static DC field, three regimes have been observed: no rotation occurs below a critical threshold field intensity, oscillatory motion takes place just above this value and continuous rotation can be observed above the critical threshold field intensity. It was also found that low frequency AC fields could also induce angular deformation.

A finite-strain constitutive theory for electro-active polymer composites via homogenization

This paper presents a homogenization framework for electro-elastic composite materials at finite strains. The framework is used to develop constitutive models for electro-active composites consisting of initially aligned, rigid dielectric particles distributed periodically in a dielectric elastomeric matrix. For this purpose, a novel strategy is proposed to partially decouple the mechanical and electrostatic effects in the composite. Thus, the effective electro-elastic energy of the composite is written in terms of a purely mechanical component together with a purely electrostatic component, this last one dependent on the macroscopic deformation via appropriate kinematic variables, such as the particle displacements and rotations, and the change in size and shape of the appropriate unit cell. The results show that the macroscopic stress includes contributions due to the changes in the effective dielectric permittivity of the composite with the deformation. For the special case of a periodic distribution of electrically isotropic, spherical particles, the extra stresses are due to changes with the deformation in the unit cell shape and size, and are of order volume fraction squared, while the corresponding extra stresses for the case of aligned, ellipsoidal particles can be of order volume fraction, when changes are induced by the deformation in the orientation of the particles.

The compressive electrical field electrostrictive coefficient M33 of electroactive polymer composites and its saturation versus electrical field, polymer thickness, frequency, and fillers

Electroactive polymers are widely studied because of their large electrical‐field‐induced strain. Their flexibility and their ability to be deposited on large surfaces make them promising candidates as electroactive materials for actuators or energy‐harvesting devices. For actuation purposes, the material efficiency is directly related to the electrical‐field‐related electrostrictive coefficient M33 through S33 = M33E2, where S33 is the electrical‐field‐induced strain and E is the applied electrical field. Numerous studies concern the increase of M33, but very few have been devoted to its saturations versus electrical field. To this end, the present paper describes the variation of M33 versus thickness, composition, frequency, and electrical field for polyurethane‐based composites. Based on the saturation of the electrical‐field‐induced polarization within the studied polymer composites, a model of the M33 behavior was also proposed, and it was found to show a good agreement with the experimental data. In addition, this model predicts the dielectric constant and the saturation electrical field to be the key parameters ruling the M33 saturation. Copyright © 2011 John Wiley & Sons, Ltd.

Electroluminescent polymer nanomaterials and structures based on J aggregates

566 An important line in the design of new high-molecular-weight structures with electroluminescent properties is the study of electroactive polymer composites containing a particular type of organic nanosized crystals with semiconductor properties known as J aggregates. Such polymer composites possess a number of advantages as compared to polymer systems doped with low-molecular-weight luminophores or inorganic nanosized particles [1, 2]. We have developed and studied electroluminescent layers doped with nanocrystals of cyanine dye (CD) J aggregates. These particles are efficient luminophores [3] and are used as spectral sensitizers of photographic materials [4].

Modeling Ionic Continua Under Multifield Conditions

Recent advances in the development of electroactive polymer materials and composites along with the need for new multifunctional exploitation of these materials have underlined the need for the multi-field modeling of their behavior. Behavioral modeling of these materials is essential for design, material qualification, and material certification for sensing, actuation, and energy harvesting applications. The present paper proposes and applies a methodology for modeling the behavior of ionic continua under multi-field influence at the macro length scale. The computational implementation of this methodology addresses generation and solution of both the constitutive and the field evolution equations by appropriate use of continuum mechanics, irreversible thermodynamics, and electrodynamics. An application of this methodology for the case of electric multi-component anisotropic hygrothermoelasticity generates a constitutive model for a large class of materials capable of actuation, sensing, and energy harvesting applications. A specialization of this theory for isotropic and bi-component chemo-thermo-electro-elastic materials is provided along with the corresponding field equations. To demonstrate the capabilities of this approach for realistic applications, a system of nonlinear governing partial differential equations is derived to describe the state evolution of large deflection plates made from such material systems. These equations represent the electro-hygro-thermal generalization of the well-known von-Karman equations for large deflection plates and capture the actuating behavior of these plates. Finally, numerical solutions of these equations for two sets of boundary conditions are presented to demonstrate solution feasibility and realism of modeling in the context of actuation-based applications.