Electronic Electroactive Polymers Research Articles

On the influence of free space in topology optimization of electro-active polymers

This study investigates the impact of the surrounding free space on the topology optimization (TO) of electro-active polymers (EAPs). It is well understood that, under the application of an electric field, the deformation of an EAP is not solely determined by the field distribution within the body, but also by the distribution in the free space surrounding it. This is particularly true for electronic EAP, which are emerging as leading candidates for developing artificial muscles. Our study specifically focuses on understanding the influence of the free space in the context of density-based TO. We model the free space as an extended void region around the design domain. Our numerical experiments focus on EAP actuators and take into account their geometrical nonlinear behavior. The results show that incorporating the surrounding free space has a significant impact on the performance of the optimized EAPs with low electric permittivity. This makes it essential to consider in real-world applications.

Recent Progress on Electroactive Polymers: Synthesis, Properties and Applications

Electroactive polymers (EAPs) are an advanced family of polymers that change their shape through electric stimulation and have been a point of interest since their inception. This unique functionality has helped EAPs to contribute to versatile fields, such as electrical, biomedical, and robotics, to name a few. Ionic EAPs have a significant advantage over electronic EAPs. For example, Ionic EAPs require a lower voltage to activate than electronic EAPs. On the other hand, electronic EAPs could generate a relatively larger actuation force. Therefore, efforts have been focused on improving both kinds to achieve superior properties. In this review, the synthesis routes of different EAP-based actuators and their properties are discussed. Moreover, their mechanical interactions have been investigated from a tribological perspective as all these EAPs undergo surface interactions. Such interactions could reduce their useful life and need significant research attention for enhancing their life. Recent advancements and numerous applications of EAPs in various sectors are also discussed in this review.

Computational structural and material stability analysis in finite electro‐elasto‐statics of electro‐active materials

SummaryDielectric materials like electro‐active polymers (EAPs) exhibit coupled electro‐mechanical behavior at large strains. They respond by a deformation to an applied electrical field and are used in advanced industrial environments as sensors and actuators, for example, in robotics, biomimetics and smart structures. In field‐activated or electronic EAPs, the electric activation is driven by Coulomb‐type electrostatic forces, resulting in Maxwell stresses. These materials are able to provide finite actuation strains, which can even be improved by optimizing their composite microstructure. However, EAPs suffer from different types of instabilities. This concernsglobal structural instabilities, such as buckling and wrinkling of EAP devices, as well aslocal material instabilities, such as limit‐points and bifurcation‐points in the constitutive response, which induce snap‐through and fine scale localization of local states. In this work, we outline variational‐based definitions for structural and material stability, and design algorithms for accompanying stability checks in typical finite element computations. The formulation starts from stability criteria for acanonical energy minimization principleof electro‐elasto‐statics, and then shifts them over to representations related to anenthalpy‐based saddle point principlethat is considered as the most convenient setting for numerical implementation. Here, global structural stability is analyzed based on aperturbation of the total electro‐mechanical energy, and related to statements of positive definiteness of incremental finite element tangent arrays. We base the local material stability on anincremental quasi‐convexity conditionof the electro‐mechanical energy, inducing the positive definiteness of both the incremental electro‐mechanical moduli as well as a generalized acoustic tensor. It is shown that the incremental arrays to be analyzed in the stability criteria appear within the enthalpy‐based setting in adistinct diagonal form, with pure mechanical and pure electrical partitions. Applications of accompanying stability analyses in finite element computations are demonstrated by means of representative model problems. Copyright © 2015 John Wiley & Sons, Ltd.

Modeling and simulation of viscous electro-active polymers

Electro-active materials are capable of undergoing large deformation when stimulated by an electric field. They can be divided into electronic and ionic electro-active polymers (EAPs) depending on their actuation mechanism based on their composition. We consider electronic EAPs, for which attractive Coulomb forces or local re-orientation of polar groups cause a bulk deformation. Many of these materials exhibit pronounced visco-elastic behavior. Here we show the development and implementation of a constitutive model, which captures the influence of the electric field on the visco-elastic response within a geometrically non-linear finite element framework. The electric field affects not only the equilibrium part of the strain energy function, but also the viscous part. To adopt the familiar additive split of the strain from the small strain setting, we formulate the governing equations in the logarithmic strain space and additively decompose the logarithmic strain into elastic and viscous parts. We show that the incorporation of the electric field in the viscous response significantly alters the relaxation and hysteresis behavior of the model. Our parametric study demonstrates that the model is sensitive to the choice of the electro-viscous coupling parameters. We simulate several actuator structures to illustrate the performance of the method in typical relaxation and creep scenarios. Our model could serve as a design tool for micro-electro-mechanical systems, microfluidic devices, and stimuli-responsive gels such as artificial skin, tactile displays, or artificial muscle.

On the spatial and material motion problems in nonlinear electro-elastostatics with consideration of free space

In this work the formulation of spatial and material motion problems in nonlinear electro-elastostatics is considered using an energy approach, which takes into account the contribution of the free space surrounding a nonlinearly polarized body undergoing large deformation. The free space can have a huge impact on the electric field and on the deformation field inside a body made of materials with low electric permittivity such as the so-called electronic electroactive polymers (EEAPs). The contribution of the free space can be taken into account by using the electric flux and the Maxwell's traction acting on the boundary of the body. These two quantities can be expressed in terms of a stored energy density function. By using a stored energy density function for both the material body and the (finite or infinite) free space, the governing equations of both spatial and material motion problems are derived by considering the change of energy with respect to a change in the spatial or material configuration. In the spatial motion problem, well-known definitions for electric and mechanical quantities are derived. In the material motion problem, in addition to the derivation of configurational forces, this approach reveals the formulas for the part of energy that is released from the system material body, applied forces in response to a change in the material configuration, which are particularly useful in the study of defects such as crack propagation. The same approach can be used in the case of nonlinear electro-thermo-mechanical coupling and constitutes the direction for future works.

Dielectric elastomers as next-generation polymeric actuators.

Due to their versatile properties, robust behavior, facile processability and low cost, organic polymers have become the material of choice for an increasing number of mature and cutting-edge technologies. In the last decade or so, a new class of polymers capable of responding to external electrical stimulation by displaying significant size or shape change has emerged. These responsive materials, collectively referred to as electroactive polymers (EAPs), are broadly classified as electronic or ionic according to their operational mechanism. Electronic EAPs generally exhibit superior performance relative to ionic EAPs in terms of actuation strain, reliability, durability and response time. Among electronic EAPs, dielectric elastomers exhibit the most promising properties that mimic natural muscle for use in advanced robotics and smart prosthetics, as well as in haptic and microfluidic devices. Elastomers derived from homopolymers such as acrylics and silicones have received considerable attention as dielectric EAPs, whereas novel dielectric EAPs based on selectively swollen nanostructured block copolymers with composition-tailorable properties have only recently been reported. Here, we provide an overview of various EAPs in terms of their operational mechanisms, uses and shortcomings, as well as a detailed account of dielectric elastomers as next-generation actuators.