Carbon nanotubes (CNTs) show an active behavior when they are positioned within an electric field, immersed into an electrolyte and charged. Several explanations are given, ranging from nanoscopic to macroscopic effects. This paper presents experimental proven explanations of the paper actuation and results using continuous CNTs of a CNT-array. For the first test series specimens are cut off a paper manufactured of single-walled, μ-long CNTs working in series. The second test series uses specimens which are prepared of free standing multi-walled CNTs. Their CNT lengths reach macroscopic dimensions of almost 3 mm and they can be considered as connected in parallel. Both series are electromechanically tested. The paper tests reveal their strong condition-dependent microstructure. Generally, the observed effects can be explained by diffusion of ions into the flexible CNT microstructure. In contrast, the CNT-array based specimens show almost no condition dependency which can be explained by the strong carbon bonds. Due to specimen orientation and test set-up, macroscopic effects can be excluded. The found actuation can be attributed to an elongation of the carbon structure as result of ion-interaction. However, it must be assumed that there are further superimposing effects which might not be distinguished from each other down to the last detail.

The orientation and spatial distribution of magnetic particles in smart mechano-magnetic composites are key to enhancing their actuation capability. In this study, we present a new experimental approach to tune the orientation and assembly of barium hexaferrite (BHF) micro-platelets in liquid polymers by applying uniform magnetic and alternating current (AC)-electric fields. First, we investigated the assembly of BHFs under different electric field amplitudes and frequencies in the silicone elastomer. After establishing the optimum parameters for electric and magnetic alignment, four different microstructures are fabricated namely (a) random (b) electrically aligned (c) magnetically aligned and (d) simultaneously electrically and magnetically aligned. Finally, microstructural and property characterizations are performed using OM, XRD, SEM, and VSM measurements. Our findings demonstrate that a variety of microstructures can be obtained depending on the nature of the applied external field: in the absence of any field, BHF platelets are organized as small stacks, owing to their intrinsic magnetic polarization. In contrast, application of an electric field creates chain-like structures where the orientation of the BHF stacks inside the chains is random. Application of a magnetic field enhances rotation of the BHF stacks, which are found to rotate inside the chain in directions dictated by the magnetic field. Finally, by applying simultaneous electric and magnetic fields while also tuning the processing parameters, BHF-composite film with a squareness ratio of 0.92 is obtained. In order to further extend the actuation capability of resulting composites, we will also experiment with electroactive polymer matrices such as P(VDF–TrFE–CTFE) terpolymer to fabricate a multiferroic material that can actuate under both electric and magnetic field.

Liquid crystalline (LC) behaviors of cellulose nanocrystal (CNC), derived from wood, cotton or other cellulose-based biopolymers, have been actively investigated due to their unique optical properties and their superb mechanical properties, which open up potential applications in bioelectronics and biomedical engineering. In particular, many attempts have been made to control phase and orientation of LC-CNCs because they are critical factors deciding optical and mechanical properties, and electromechanical performances. Through the applications of mechanical force, electric field and magnetic field, some degree of success has been achieved; however, realizing homogeneous arrangements of CNCs that can be exploited at the macroscale is still elusive, owing to a variety of intermolecular interactions. The characterizations of the LC phase and orientation of CNCs are also challenging due to their complex biological structures. In this report, we introduce approaches to control the phase and orientation of LC-CNCs through the self-assembly, mechanical force and electric field. The liquid crystalline behaviors of CNCs in polar solvents and at the air/water interface are discussed. Translational and rotational behaviors of CNCs under DC electric field are also investigated as a function of their surface charge and dipole moment. In addition, we introduce a nonlinear optical process, namely, sum frequency generation (SFG) spectroscopy, for the structural characterization of LC-CNCs. Using SFG, we can analyze not only crystal phase and structure, but also polar ordering of CNCs which plays a key role in determining their electromechanical performances. Development of cellulose-based smart materials will expand the spectrum of available functional materials that are lightweight, flexible, mechanically tough, and thermally stable at moderately high temperatures (up to 300°C).

In the present article, we focus on the forced vibration and control analysis of functionally graded (FG) graphene-polymer composites bonded with piezoelectric layers considering strong electric fields. Different non-uniform gradient distributions of graphene platelets (GPLs) are assumed through the thickness direction. The Modified Halpin-Tsai micromechanics model is used to obtain the effective material properties of GPL/polymer composites. Electromechanical coupling of piezoelectric layers is described by two rotationally invariant non-linear constitutive relations. A four-node shell element considering transverse shear effect based on the Reissner-Mindlins hypothesis has been developed for forced vibration and control analysis of smart FG-GPL/composites using the principle of virtual work considering nonlinear material law for the piezoelectric layers. The developed element is verified and compared with the numerical results those available in the literature. Different configurations of FG-GPL composite shells have been analysed and discussed to compare in terms of settling time, first resonance frequency and absolute amplitude corresponding to first resonant frequency by carrying out time and frequency response analysis, and the effects of weight fraction of GPLs on vibration response of such shell structures are also discussed. The influence of electromechanical nonlinear constitutive relations is also presented and discussed by performing active control analysis on different FG-GPL composite shell structures. Moreover, the results show that the GPL distribution and weight-fraction of GPLs have a significant effect on the vibration and damping characteristics of the FG-GPL composite shell structures.

Multi-layered, self-actuated devices have been the focus of recent studies due to their ability to exhibit large displacements and achieve complex shapes. Such devices have been constructed using active materials responsive to varying stimuli including electro-active and magneto-active materials to perform useful functions or satisfy objective functions related to target shapes. In this work, the authors seek to study the utility of employing materials responsive to magnetic and electric fields in combination with passive materials, and with varied placement in discrete layers and segments through a flexible beam, to design structures capable of satisfying a variety of objective functions simultaneously. These multi-field responsive composite devices, with greater complexity of the embedded combined actuation mechanisms, are able to achieve a wider variety of target shapes compared to traditional unimorph/bimorph structures actuated by a single-field. Additionally, the increased actuation design space facilitates consideration of a wider range of possible objective functions including those related to power consumption, materials’ cost, and work performed. Fabrication of these devices for experimentation is both time-consuming and expensive. As a result, this study will utilize an existing one-dimensional model for electromagnetically-actuated composites and expand its features to include segmentation: the arbitrary placement of any active or passive material type in any layer of a given arbitrarily-sized section of the beam. Ultimately, the goal of this study is to analyze the model by varying characteristic features of multi-field actuated, multi-layered, and segmented devices undergoing large displacements under simultaneously applied fields. Although the model is written arbitrarily for any number of segments, layers within segments, and material types, this study focuses on a base model comprising three material types: electroactive polymer, magneto-active elastomer, and a passive substrate. The initial parameters chosen for the study are the relative lengths (length ratio) of segments, volume of magnetic material, and stiffness of passive material. Two objective functions are chosen. The first is a target shape approximation function, dependent on the errors between the displacements of the computed and the desired shapes. The second calculates a cost based on volume of magnetic material. The effects of the parameters on the objective functions are analyzed by evaluating an array of combinations of parameters; results indicate that each parameter significantly influences the multi-field actuation of the beam, and these correlations are quantitatively analyzed and compared. Concurrently, metrics of power required, structure mass, and other important factors are quantified. As a result, this analysis serves as a precursor to a formal optimization algorithm by determining the usefulness of the chosen objective functions and corresponding input variables for these devices, while also identifying other possible metrics for the design optimization of a multi-field beam.

Glass Fiber Reinforced Polymer (GFRP) beams have shown over a 20% decrease in weight compared to more traditional materials without affecting system performance or fatigue life. These beams are being studied for use in automobile leaf-spring suspension systems to reduce the overall weight of the car therefore increasing fuel efficiency. These systems are subject to large amplitude mechanical vibrations at relatively constant frequencies, making them an ideal location for potential energy scavenging applications. This study analyses the effect on performance of GFRP beams by substituting various composite layers with piezoelectric fiber layers and the results on deflection and stiffness. Maximum deflection and stress in the beam is calculated for varying the piezoelectric fiber layer within the beam. Initial simulations of a simply supported multimorph beam were run in ABAQUS/CAE. The beam was designed with symmetric piezoelectric layers sandwiching a layer of S2-glass fiber reinforced polymer and modeled after traditional mono leaf-spring suspension designs with total dimensions 1480 × 72 × 37 mm 3 , with 27 mm camber. Both piezoelectric and GFRP layers had the same dimensions and initially were assumed to have non-directional bulk behavior. The loading of the beam was chosen to resemble loading of a leaf spring, corresponding to the stresses required to cycle the leaf at a stress ratio between R = 0.2 and 0.4, common values in heavy-duty suspension fatigue analysis. The maximum stresses accounted for are based on the monotonic load required to set the bottom leaf surface under tension. These results were then used in a fiber orientation optimization algorithm in Matlab. Analysis was conducted on a general stacking sequence [0°/45°] s , and stress distributions for cross ply [0°/90°] s , and angle ply [+45°/−45°] s were examined. Fiber orientation was optimized for both the glass fiber reinforced polymer layer to maximize stiffness, and the piezoelectric fiber layers to simultaneously minimize the effect on stiffness while minimizing deflection. Likewise, these fibers could be activated through the application of electric field to increase or decrease the stiffness of the beam. The optimal fiber orientation was then imported back into the ABAQUS/CAE model for a refined simulation taking into account the effects of fiber orientation on each layer.

Electroactive polymers are a class of materials capable of reallocating their shape in response to an electric field while also having the ability to harvest electrical energy when the materials are mechanically deformed. Electroactive polymers can therefore be used as sensors, actuators, and energy harvesters. The parameters for manufacturing flexible electroactive polymers are complex and rate limiting due to number of steps, their necessity, and time intensity of each step. Successful 3D printing manufacturing processes for electroactive polymers will allow for scalability and flexibility beyond current limitations, improving the field, opening additional manufacturing possibilities, and increasing output. The goal for this research is to use additive manufacturing techniques to print conductive and dielectric substrates for building flexible circuits and sensors. Printing flexible conductive layers and substrates together allows for added creativity in design and application. In this work we have successfully demonstrated additive production of a simple flexible circuit using exclusively additive manufacturing.

An electroactive polymer is a material capable of changing its size and shape when an electric field is present. It is composed of a thin film of dielectric elastomer and two electrodes placed on the top and bottom of the dielectric material. Since the rediscovery of their capabilities, electroactive polymers have been proposed as novel materials for use in numerous fields such as in bioengineering, electronics, hydraulics, and aerospace. It has been demonstrated that the actuation potential of electroactive polymer dielastomers can be significantly enhanced by mechanically pre-straining the material prior to application of an electric field. Application of uniform pre-strain is critical for uniform actuation and is challenging to achieve. This research details methods for constructing an automated uniform stretcher that resulted in the production of a LabView controlled iris stretcher for flexible materials. The high torque stretcher was capable of pre-straining materials with a minimum diameter of 1 inch mm) to a maximum diameter of 16 inches. The stretcher calculates the percent strain and has adjustable speed control through a high torque micro-stepper motor and controller. The stretcher’s capabilities were demonstrated on materials within varying tensile strengths up to 725 psi.

This paper presents the development process of an electrically insulating and liquid-impermeable coating for piezoelectric actuators. Against the background of flow investigations of an adaptive airfoil in a water tunnel the adaptive lip including PZT-ceramics for the active lip deformation must be insulated and sealed up against the ingress of moisture. Due to high electric field strength of 2 kV/mm between electrodes of multilayer actuators any ingress of moisture would lead to a reduction of the dielectric strength and may cause a short circuit. In order to prevent failure of the adaptive lip the electrical connections of the actuators have to be insulated by a waterproof coating. A service life of at least 10 7 load cycles at a frequency of 100 Hz is required for the actuators. Therefore the coating should be as ductile as possible otherwise it could crack and water could diffuse into the actuators. That is why the yield strength of the coating has to be higher than of the actuators, which is 0.3 %. For the investigation of the waterproofness several samples are coated with different materials in various processes. First the actuators are moulded in epoxy resin and then a diffusion-resistant PVF-foil is applied. After a screening of different materials, an additional coating with a two-component tar-epoxy resin in combination with a gold coating applied by a PVD process seems to be the most suitable process. Another promising waterproof coating is the atomic layer deposition (ALD). It is a slightly changed chemical vapor deposition (CVD) and referring to the studies of Abdulagatov et al. an ALD of aluminum oxide (Al 2 O 3 ) and titanium dioxide (TiO 2 ) can slow down the corrosion of static copper specimens in water for ∼80 days [1]. Through a redrying procedure during test intermissions an increased underwater service life of the piezoelectric actuators is achieved.

Several biological creatures represent a great inspiration for the realization of advanced morphing materials. For instance, bat wing is extremely interesting because of its unique ability of drastically changing shape and size thanks to an embedded distributed array of ultra-small-in-size muscles. This is obviously done as a response to continuously detected external stimuli. Novel ultra-lightweight and non-invasive artificial muscles that can exploit a dual functionality and that can be integrated into hosting materials, are here investigated. The muscles are made of a piezoelectric (PVDF) single micro-fibre and a micro-fibre rope created using a simple electrospinning technique. The advantage of this technique is the less-complex in-situ fibres poling during electrospinning which makes them an attractive alternative compared to thin PVDF films that require an additional complicated poling step to achieve their piezoelectric properties. Muscles that possess an active and passive electromechanical response based on a ∼ 3-micron thick single PVDF fibre and ∼ 150-micron thick PVDF fibred rope, were realized. Preliminary results prove that these PVDF fibres have a highly accurate electromechanical response over an extremely wide frequency range. Fully constrained single fibres and fibre ropes, when actuated with the corresponding electric fields, show a midpoint displacement of ∼ 36 μm.

In this study, we demonstrate the electric and magnetic manipulation of nanoscale M-type Barium Hexaferrite (nBF) in polydimethylsiloxane (PDMS) to engineer a multifunctional nanocomposite with improved dielectric and magnetic properties. First, we synthesized the single crystal nBF via the hydrothermal synthesis route. The hydrothermal temperature, duration, and surfactant conditions were optimized to improve the magnetic properties of the nBFs, with further improvement achieved by post-annealing. The annealed nBFs were aligned dielectrophoretically (DEP) in the polymer matrices by applying an AC electric field. Under the influence of this electric field, nBFs were observed to rotate, align and form chains within the polymer matrix. Optical microscopy (OM) imaging was used to determine the electrical alignment conditions (duration, magnitude, and frequency) and these parameters were used to fabricate the composites. A Teflon setup with Indium Tin Oxide (ITO) coated Polyethylene Terephthalate (PET) was used, where the ITO coatings act as electrodes for the electric field-manipulation. To simultaneously apply the magnetic field, this Teflon setup is placed between two permanent magnets capable of generating a 0.6 T external magnetic field. Along with electric and magnetic fields, concurrent heating was applied to cure the PDMS and freeze the microstructure formed due to electric and magnetic fields. Upon completion of the curing step, parallel chain formation is observed under OM. The X-Ray Diffraction (XRD) results also confirm that the particles are magnetically oriented in the direction of the magnetic field within the chain. Vibrating Sample Magnetometry (VSM) measurements and dielectric spectroscopy are used to characterize the extent of anisotropy and improvement in dielectric and magnetic properties compared to random composites. We find that simultaneous electric and magnetic field alignment improves the dielectric properties by 12% compared to just magnetic alignment. We also observe 19% improved squareness ratio when both fields are applied. The possibility of simultaneous electrical and magnetic alignment of magnetic nanoparticles will open up new doors to manipulate and design particle-modified polymers for various applications.

Field induced phase transformations in ferroelectric crystals occur when the applied electrical or mechanical load exceeds a certain threshold. Mechanical cycling about these transformation field thresholds under varying open and closed circuit conditions has been shown to yield a near ideal mechanical to electrical energy harvesting technique. Numerical integration of experimentally measured stress – strain and electric field – electric displacement data has shown mechanical to electrical energy conversion efficiency near 60% for 0.24PIN-0.44PMN-0.32PT. In this work, the total irreversible energy is determined by the offset between the forward and reverse loading paths, equivalent to the hysteresis in the phase transformation behavior. This is equal to the available mechanical energy for conversion to electrical energy for harvesting. Following the ideal mechanical to electrical energy harvesting procedure, the total possible energy harvested is a direct function of the hysteresis area in the phase transformation and the electromechanical coupling factor. Efficiency is predicted to be equal to the electromechanical coupling factor, 0.596 (59.6%). Predicted results agree with experimental data from numerical integration. Energy densities are calculated up to 5 kJ/m 3 with potential power densities of 10 2 –10 3 kW/m 3 .

Ionomers are a class of polymers which contain a small fraction of charged groups in the polymer backbone. These ionic groups aggregate (termed ionic aggregates) to form temporary cross-links that break apart over the ionic dissociation temperature and re-aggregate on cooling, influencing the mechanical properties of these polymers. In addition to enhanced mechanical properties, some ionomers also exhibit self-healing behavior. The self-healing behavior is a consequence of weakly bonded ionic aggregates breaking apart and re-aggregating after puncture or a ballistic impact. The structure and properties of ionomers have been studied over the last several decades; however, there is a lack of understanding of the influence of an electrostatic field on ionic aggregate morphology. Characterizing the effect of temperature and electric field on the formation and structure of these ionic aggregates will lead to preparation of ionomers with enhanced structural properties. This work focuses on Surlyn 8940 which a poly-ethylene methacryclic acid co-polymer in which a fraction of the carboxylic acid is terminated by sodium. In this work, Surlyn is thermoelectrically processed over its ionic dissociation temperature in the presence of a strong electrostatic field. Thermal studies are performed on the ionomer to study the effect of the thermoelectric processing. It is shown that the application of a thermoelectric field leads to increase in the ionic aggregate order in these materials and reduction in crystal size distribution. Thermal Analysis is performed using a Differential Scanning Calorimeter and the resulting thermogram analysis shows that thermoelectric processing increases the peak temperature and onset temperature of melting by 4 C and 20 C respectively. The peak width at half maximum of the melting endotherm is reduced by 10 C due to thermoelectric processing. This serves as a measure of the increased crystallinity. A parametric study on the effect of field duration and field strength is also performed.

Active origami designs, which incorporate smart materials such as electroactive polymers (EAPs) and magnetoactive elastomers (MAEs) into mechanical structures, have shown good promise in engineering applications. In this study, finite element analysis (FEA) models are developed using COMSOL Multiphysics software for two configurations that incorporate a combination of active and passive material layers, namely: 1) a single-notch unimorph folding configuration actuated using only external electric field and 2) a bimorph configuration which is actuated using both electric and magnetic (i.e. multifield) stimuli. Constitutive relations are developed for both electrostrictive and magnetoactive materials to model the coupled behaviors directly. Shell elements are adopted for their capacity of modeling thin films, reduction of computational cost and ability to model the intrinsic coupled behaviors in the active materials under consideration. A microstructure-based constitutive model for electromechanical coupling is introduced to capture the nonlinearity of the EAP’s relaxor ferroelectric response; the electrostrictive coefficients are then used as input in the constitutive modeling of the coupled behavior. The magnetization of the MAE is measured by experiment and then used to calculate magnetic torque under specified external magnetic field. The objective of the study is to verify the effectiveness of the constitutive models to simulate multi-field coupled behaviors of the active origami configurations. Through quantitative comparisons, simulation results show good agreement with experimental data, which is a good validation of the shell models. By investigating the impact of material selection, location, and geometric parameters, FEA can be used in design, reducing trial-and-error iterations in experiments.

Relaxor ferroelectric polymers are a unique branch of electro-active polymers (EAPs) that generate high electromechanical strain with relatively low hysteresis and high nonlinearity. Polyvinylidene fluoride-based EAPs possess these qualities due to the semicrystalline nature of their microstructure. The interactions of electric dipoles within the microstructure of the material generate large strains under an external electric field, and the reduced crystalline domain sizes yield a relaxor effect by exhibiting low hysteresis and hyperelastic properties. This phenomenon has been partially modeled by previous works, but micro-electro-mechanisms for electrostriction in the microstructure have been largely ignored. This study focuses on the effects of various microstructural frameworks on the nonlinear dielectric behavior of dipole-based, semicrystalline EAPs. The Helmholtz free energy function of a microscopic representative volume element (RVE) is composed of an electrostatic energy and an elastic energy. The dipole-dipole interaction energy is prescribed for the electrostatic forces observed among the crystalline regions, and the elastic component attributed to the relaxation of the amorphous phase is modeled by the hyperelastic eight-chain model, which is microstructure-based. The RVE of the system is modeled by a central dipole surrounded by dipoles whose relative spatial locations are determined by a probability distribution function (PDF). The hyperelastic amorphous phase constitutes the volume separating the central and surrounding dipoles. The free energy of the RVE is implemented into a continuum description of the equilibrium of the system to obtain electromechanical relations. Additionally, this electromechanical response data is applied to a 1D structural mechanics model for simulating the large deformation of a multi-layered beam. The effects of microstructure on electrostrictive coupling are explored by varying the centers and deviations of dipole locations within the PDF. Discrete microstructural arrangements representing 3-chain network averaging schemes may be studied alongside more continuous ellipsoidal or random models of dipole spatial arrangements. The simulation results of the PDF-based networks are in good agreement with experimental data. The results indicate that the electrostrictive behavior of EAPs is strongly dependent on (1) the relative dipole spatial locations and (2) the extent of the regions containing dipoles, which represent crystalline domains. The model finds that adding extra crystalline domains in the network averaging schemes generates a better characteristic behavior due to a broader averaging of spatial orientations. These results offer a gateway to predicting microstructurally-dependent dipole-based behavior that can lead to the predictive theoretical tailoring of microstructures for desired electromechanical properties.

The Maximum Entropy (ME) method is shown to provide a new approach for quantifying model uncertainty in the presence of complex, heterogeneous data. This is important in model validation of a variety of multifunctional constitutive relations. For example, multifunctional materials contain field-coupled material parameters that should be self-consistent regardless of the measurement. A classical example is piezoelectricity which may be quantified from charge induced by stress or strain induced by an electric field. The proposed tools provide new statistical information to address measurement discrepancies, guide model development, and catalyze materials discovery for data fusion problems. The error between the model outputs and heterogeneous data is quantified and used to formulate a second moment constraint within the entropy functional. This leads to an augmented likelihood function that weights each individual set of data by its respective variance and covariance between each data set. As a first step, the method is evaluated on a piezoelectric ceramic to illustrate how the covariance matrix influences piezoelectric parameter estimation from heterogeneous electric displacement and strain data.

In this paper, we discuss the development and implementation of a 3-D electromechanically coupled homogenized energy model (HEM) for ferroelectric materials. A stochastic-based methodology is introduced and applied to problems involving large scale switching of ferroelectric and ferroelastic materials. Switching criteria for polarization variants are developed using density distributions in three dimensions to accommodate both electrical and mechanical loading and their coupled response. The theory accommodates non-proportional loading and major/minor loop hysteresis. Such formulations are known to accelerate computations for real-time control of nonlinear and hysteretic actuators. The proposed formulation maintains superior computational efficiency in the three dimensional case through the application of density formulations that are based on internal distributions of stress and electric field to produce a distribution of polarization switching events over a range of applied fields and stresses.

Compared to clinic-based systems, rehabilitation robots designed for home use could enable increased accessibility and intensity of therapy for stroke survivors. To move upper extremity rehabilitation robots from the clinic to the home, the designs must become smaller, lighter, and less complex. One path to reducing the size of the robot’s hardware is to replace conventional actuators with smaller designs utilizing the unique properties of smart materials. As a first step towards reducing the size of upper extremity rehabilitation robots, this paper presents results from a characterization study of a prototype electrorheological fluid. The fluid’s dynamic yield stress was first measured using a modified controlled stress rheometer. A testbed was then developed to analyze the mechanical performance of a custom brake filled with the fluid. System parameters measured included braking torque at varying electric field strengths as well as the fluid’s speed of response. Maximum torque output was 4.80 N-m at an electric field strength of 3 kV/mm. Experimental results also indicate that the fluid’s activation and relaxation times will enable sufficient control bandwidth for the desired application. However, non-linear effects, such as field-dependent hysteresis, are significant and may require compensation from the controller supervising interaction between the robot and patient.

Active Fiber Composites (AFCs) are piezoelectric devices comprised of long cylindrical fibers, typically made of ceramic lead zirconate titanate (PZT), embedded in an epoxy polymer. AFCs use interdigitated electrodes to produce electric field lines parallel to the fibers (33-mode) rather than across the diameter, exploiting the stronger out-of-plane electromechanical coupling. Nonlinear piezoelectric and dielectric terms and non-uniform poling are often neglected in modeling AFCs due to the added complexity, however including the terms improves accuracy for strong electric fields and where the electrode geometry causes non-uniform electric fields. For that reason, a new finite element model of the AFC is developed which includes the effect of nonlinearities in piezoelectric strain constants and electric permittivity due to a non-uniform applied electric field resulting from two sets of interdigitated electrodes. The methods used to apply the nonlinear constitutive equations and poling are described. A comparison of the AFC response with linear and nonlinear material properties, with non-uniform poling, is shown for increasing applied electric fields. The difference in AFC response illustrates the necessity to include Rayleigh Law terms and non-uniform poling in the model.

ZnO based polymer composite materials are of great interest because of their excellent electrical, optical, semiconductor and biocompatible properties. In this study, we synthesize anisotropic composites of aligned ZnO rods in polydimethylsiloxane (PDMS) elastomer and study their dielectric properties as a function of applied electric field and frequency. Submicron ZnO rods are synthesized using an inexpensive, high yield chemical route. Washed and purified ZnO rods are then aligned in uncured PDMS at different electric field and frequency. We find that under electric field, ZnO rotates with their long axis in the direction of the electric field and before coalescing form chains in the silicone elastomer. From the optical microscopy images and in situ dielectric measurements, the best alignment parameters are found at 4 kV/mm and 10 kHz. These conditions are then selected to prepare aligned ZnO-PDMS composites. Complete curing of composites is confirmed using dynamic mechanical analysis (DMA). Our results show that aligned ZnO in uncured PDMS exhibit higher dielectric permittivity compared to random dispersion with the same composition. For the cured ZnO-PDMS composites, dielectric permittivity increases by 80% compared to random composites.