Electroactive Polymer Membrane Research Articles

Deformable Joule Heating Electrode Based on Hybrid Layers of Silver Nanowires and Carbon Nanotubes and its Application in a Refreshable Multi‐Cell Braille Display

AbstractJoule heating electrodes (JHEs) are required for thermal actuation systems. A highly stretchable, patternable, and low‐voltage operating JHE based on hybrid layers of silver nanowires and carbon nanotubes are reported. The conductive layers are applied on a locally pre‐strained bistable electroactive polymer (BSEP) membrane to form a wrinkled conductive surface with a low resistance of 300 Ω/sq, and subsequently patterned to a serpentine trace by laser engraving. The resistance of the resulting JHE electrode remains nearly unchanged up to 80−90% area strain. By applying a voltage of 7 − 9 V to the electrode, the temperature of the BSEP membrane increased to ~60 °C, well above the polymer's phase transition temperature of 46 °C, thereby lowering its modulus by a factor of 103. An electronic Braille device based on the JHEs on a BSEP membrane is assembled with a diaphragm chamber. The electrode is patterned into 3 × 2 individually addressable pixels. Through Joule heating of the pixels and local expansion of the BSEP membrane using a pneumatic pressure, the pixels deformed out of the plane by over 0.5 mm to display Braille letters. The Braille content can be refreshed for 20 000 cycles at the same operating voltage.

Simulation Analysis of Equibiaxial Tension Tests for Rubber-like Materials.

For rubber-like materials, there are three popular methods of equibiaxial tension available: inflation tension, equibiaxial planar tension, and radial tension. However, no studies have addressed the accuracy and comparability of these tests. In this work, we model the tension tests for a hyperelastic electroactive polymer (EAP) membrane material using finite element method (FEM) and investigate their experimental accuracy. This study also analyzes the impact of apparatus structure parameters and specimen dimensions on experimental performances. Additionally, a tensile efficiency is proposed to assess non-uniform deformation in equibiaxial planar tension and radial tension tests. The sample points for calculating deformation in inflation tensions should be taken near the top of the inflated balloon to obtain a more accurate characteristic curve; the deformation simulation range will be constrained by the material model and its parameters within a specific limit (λ ≈ 1.9); if the inflation hole size is halved, the required air pressure must be doubled to maintain equivalent stress and strain values, resulting in a reduction in half in inflation height and decreased accuracy. The equibiaxial planar tension test can enhance uniform deformation and reduce stress errors to as low as 2.1% (at λ = 4) with single-corner-point tension. For circular diaphragm specimens in radial tension tests, increasing the number of cuts and using larger punched holes results in more uniform deformation and less stress error, with a minimum value of 3.83% achieved for a specimen with 24 cuts and a 5 mm punched hole. In terms of tensile efficiency, increasing the number of tensile points in the equibiaxial planar tension test can improve it; under radial tension, increasing the number of cuts and decreasing the diameter of the punched hole on the specimen has a hedging effect. The findings of this study are valuable for accurately evaluating various equibiaxial tension methods and analyzing their precision, as well as providing sound guidance for the effective design of testing apparatus and test plans.

Equibiaxial Planar Tension Test Method and the Simulation Analysis for Hyperelastic EAP Membrane

The equibiaxial planar tension test is an important method for determining the mechanical properties of hyperplastic membranes, and it is also critical to designing an effective equibiaxial tension test rig to meet experimental accuracy requirements. However, any analysis addressing the accuracy of this test is not reported in the literature. In this paper, an equibiaxial planar tension apparatus is proposed for conducting single-corner-point tension tests on hyperelastic electroactive polymer (EAP) membranes. The experimental data were compared with those obtained from two-corner-point-fixed tension tests and fitted with nonlinear material models, and the model’s parameters were also evaluated. Finally, the widely-used finite element software ABAQUS was employed to simulate equibiaxial planar tension methods and investigate the impact of clamping mode and point number on test accuracy as well as the uniformity of overall deformation. The test results indicate that the stress-strain curves for the two tensions remain consistent across small stretch ratios. However, as the stretch ratio increases (about λ > 2.25 ) in two-corner-point-fixed tension, stress shielding may lead to a degradation of strain uniformity and result in greater stresses than single-corner-point tension. Additionally, both the three-parameter Yeoh model and the four-parameter Ogden model can provide an accurate description of the EAP membrane material. The simulation results indicate that the axial strain variation amplitudes remain below 5% within a region spanning approximately 80% of the specimen’s overall length from its center to edge and even below 1% within a region spanning 85% in the single-corner-point tension; stress inaccuracies increase with stretch ratio, while the calculated error is about 2.1% when λ = 4 in the single-corner-point tension test, which has the smallest stress error among the tests; when the number of tension points is increased, the overall deformation becomes more sufficient, and the test accuracy improves as well. The conclusions drawn from this paper will be beneficial in designing equibiaxial planar tension test rigs and analyzing their accuracy and uniformity of deformation.

Voltage-tunable surface-enhanced Raman scattering substrates based on electroactive polymeric membranes containing plasmonic nanoparticles

We describe voltage-controlled surface-enhanced Raman scattering (SERS) substrates in which the SERS-signals can be actively modulated by applying voltage. These SERS-substrates employ a dielectric electroactive polymer (D-EAP) membrane with a pair of electrically-actuated active regions. When these regions are simultaneously activated, they produce an in-plane contractile strain in the regions of the D-EAP where SERS dye-coated nanoparticles are placed. We demonstrate that SERS-signals from dye-coated silver nanoparticles, deposited on the D-EAP membrane, increases by ∼100% upon application of an actuating voltage. Upon removal of the voltage, actuated active-areas move towards their original positions, leading to a decrease in the SERS-signals.

Semi-rigid ring-shaped electrode dielectric electroactive polymer membrane as buckling actuator

We propose a semi-rigid ring-shaped electrode layout for an out-of-plane buckling actuator using a dielectric electroactive polymer (DEAP) membrane. The electrodes are patterned around the deflectable membrane as a ring, rather than the usual compliant electrodes covering the whole membrane. One electrode is defined on the rigid substrate and the counter electrode on the flexible polymer. The buckling actuation is a result of the shear forces provided by the DEAP membrane between the ring-shaped electrodes. Comparing the results for different membrane thicknesses, shapes and electrode widths, we find that membranes accumulate compression strain without obvious deflection at low electric fields and then start deflecting linearly with electric field above a threshold of about 70 V µm−1. Furthermore, only a small effective region of the electrode area, approximately four times the membrane thickness contributes to the deflection. In the paper, we derive an analytical expression for the deflection and compare the simulation to experimental data.

Structure of a Graphene-Modified Electroactive Polymer for Membranes of Biomimetic Systems: Simulation and Experiment

A model is proposed that describes the structure of water filled Nafion-graphene composite forming the body of an electroactive polymer membrane for actuators of biomimetic systems able to work in air and a liquid medium. The model predicts the growth of the ionic conductivity with increasing concentration of a graphene modifier, which is due to that the size of a part of clusters of the Nafion framework containing hydrophobic graphene flakes enlarges together with the pore size. Then the optimal concentration of the graphene modifier is reached, which provides the maximum ionic conductivity and actuation ability of the membrane as well as its elastic properties. The possibility of introducing into Nafion the modifier amount needed to improve the actuator operation is experimentally tested.

Resonant frequency tuning of electroactive polymer membranes via an applied bias voltage

Vibration-based energy harvesting may hold tremendous impact for future applications of continuous machine and structural health monitoring. Here a novel resonant frequency tuning approach is proposed where the application of a bias voltage to a pre-stretched electroactive polymer (EAP) membrane results in changes in membrane tension which can be used to adjust the resonant frequency of the membrane. The effect of the bias voltage on the EAP membrane, which induces an electrostatic pressure and corresponding reduction in membrane thickness, is determined via an analytical model of the activation response of the EAP membrane, with the results confirmed using FEM simulation in ANSYS. Through a mass-loaded circular membrane vibration model, the effective resonant frequency of the membrane can be determined as a function of changes in membrane tension due to the applied bias voltage. In the case of an EAP membrane, pre-stretch contributes to the mechanical stiffness of the system while the applied bias voltage contributes to a change in electrical stiffness of the membrane. Experimental characterization of the EAP material VHB 4910 from 3 M verified the resonant frequencies corresponding to the bias voltages predicted from the appropriate models. Given an effective system stiffness range between 598 N m−1 (when λ = 1.5, U = 0) and 266 N m−1 (when λ = 5, U = 5000), the corresponding resonant frequency tuning range for a particular circular central loaded EAP membrane device is between 31.4 to 21.8 Hz. The proposed bias voltage tuning approach for the EAP membrane may provide a novel strategy to enable resonant frequency tuning of energy harvesting devices in particular application environments.

Adaptive Helmholtz resonator based on electroactive polymers: modeling, characterization, and control

This paper presents a new concept and strategy allowing adaptive control of a membraned Helmholtz resonator (HR) embedded in a melamine foam. The designed system aims to adapt the acoustic absorption performances and transmission loss in low frequencies (<500 Hz). The proposed concept consists in replacing the resonator front wall by an electroactive polymer membrane. The stiffness of the membrane can be controlled by an electric field, resulting in a resonance frequency shift. A 2D axisymmetric numerical model based on the finite elements method is developed to characterize the complex structure-acoustic coupling between the membrane, the HR and the host foam to determine the potential of the concept. Experimental measurements are then performed in an impedance tube and compared to numerical results. A feedforward algorithm based on neural networks allows the adaptivity of the membraned HR to the acoustic excitation variation inside the impedance tube.

Design and closed-loop control of an electroactive polymer-based tunable Helmholtz resonator

A Helmholtz resonator is a passive acoustic resonator used to control a single frequency resulting from the cavity volume and the resonator neck size. The aim of the proposed study is to present a new concept and strategy of tunable Helmholtz resonator in order to enhance acoustic performances in lower frequencies (&amp;lt;500 Hz). The proposed concept consists in replacing the resonator rigid front plate by an electroactive polymer (EAP) membrane. When an electric field is applied, a change is made in the mechanical properties of the EAP membrane which induce a resonance frequency shift. A closed-loop control algorithm is developed to allow a real-time adaptability. Experimental measurements are performed on the developed prototype to determine the potential of this concept in term of acoustic absorption and Transmission Loss for low-frequency.

‘Two way’ shape memory composites based on electroactive polymer and thermoplastic membrane

A practical and facile strategy was proposed to fabricate composites that not only use the properties of individual components (commercial electroactive polymer and thermoplastic resin) to their advantage, but also produce synergy effect of ‘two way’ shape memory properties. In this design, electroactive polymer is treated as soft segment which provides actuation force via converting electrical energy to dynamic energy. Thermoplastic material serves as ‘hard segment’ to help with fixation of temporary shape thanks to its re-structuring and stiffness/modulus changing abilities through the reversible transitional temperature. Compared with traditional one way and two way shape memory materials, this composite material has the capability of changing shape without pre-programming. High shape recover property (99±0.3%.) has been obtained due to the rubber elasticity of electroactive polymer matrix. Many features could be brought up based on this design, such as accurate control over deformation by changing strength of applied electric field as well as tailorable stimulus temperature and mechanical properties.

Dielectric Electroactive Polymer Membrane Actuator with Ring-type Electrode as Driving Component of a Tactile Actuator

We present a driving concept of a tactile actuator based on a dielectric electroactive polymer using a ring-type electrode. This electrode is located around a deflectable membrane. The fabrication process and tests of the tactile actuator including integration into a hydraulic amplifier design are presented proving the concept of the novel actuation. The tactile actuator exhibits a maximum measured deflection of 124±7μm for an applied voltage of 4200V. The membrane thickness and the total thickness of the actuator including hydraulic amplifier were 30 and about 570μm, respectively.

Modeling, Identification, and Control of a Dielectric Electro-Active Polymer Positioning System

This paper deals with a positioning system based on a dielectric electro-active polymer membrane. The motion is generated by the deformation of the membrane caused by the electrostatic compressive force between two compliant electrodes applied on the surface of the polymer. This paper proposes a detailed electro-mechanical nonlinear model of the system, which is subsequently used to develop (in both time and frequency domains) various model-based feedback control laws. Accurate modeling is useful to compensate the nonlinear behavior of the actuator (caused by the material characteristics and geometry) and obtain PID controllers providing precise tracking of steps or sinusoidal reference signals. The various design strategies are compared on various experimental tests.

Electro-separation of synthetic azo dyes from a simulated wastewater using polypyrrole/polyacrylonitrile conductive membranes

Polypyrrole/polyacrylonitrile (PPy/PAN) conducting electroactive polymer membranes (CEPMs) were fabricated and evaluated for their potential use as electro-separation of synthetic azo dyes from simulated wastewaters. The PAN substrate films were prepared from a N,N-dimethylformamide (DMF) solution at 25°C. The PPy/PAN CEPMs were fabricated by synthesizing of PPy layer on both sides of the PAN substrate films from an ethanol solution containing 5wt% pyrrole monomer using aqueous FeCl3 solution as a strong oxidant. The structure and morphology of the prepared PPy/PAN membranes were investigated using Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The electrical conductivity of PPy/PAN CEPMs was measured at room temperature. The PPy/PAN CEPMs were installed in a designed electrochemical cell including two separate compartments, each with a capacity of 750cm3. The effect of applying electrical current across the prepared PPy/PAN CEPMs on the transport flux of synthetic azo dyes, i.e. Basacryl Red GL, Basacryl Blue GL and Direct Yellow 12 from the simulated wastewater was investigated. Electrochemically controlled transport of the dyes was monitored by measuring the dye concentrations in the permeate solution. The diffusion coefficients of the dyes in the PPy/PAN membranes were determined by the concentration profile of pseudo-steady state data points.

Model-based PID control of a Dielectric Electro-Active Polymer Positioning System

Abstract This paper considers a micrometric positioning system based on a dielectric electro-active polymer membrane. The motion is generated by the deformation of the membrane caused by the electrostatic compressive force between two compliant electrodes applied on the surface of the polymer. The paper suggests various model-based design strategies (in both time and frequency domains) for PID control laws, which are able to compensate the nonlinear behavior of the actuator (caused by the characteristics of the material and the annular geometry of the membrane) and obtain very precise tracking of steps or sinusoidal reference signals. The various design strategies are discussed and compared both in simulations and experiments.

Systematic approach to development of pressure sensors using dielectric electro-active polymer membranes

Dielectric electro-active polymers (DEAPs) have become attractive materials for various actuation and sensing applications due to their high energy and power density, high efficiency, light weight, and fast response speed. However, commercial development has been hindered due to a variety of constraints such as reliability, non-linear behavior, cost of driving electronics, and form factor requirements. This paper presents the systematic development from laboratory concept to commercial readiness of a novel pressure sensing system using a DEAP membrane. The pressure sensing system was designed for in-line pressure measurements for low pressure applications such as health systems monitoring. A first generation sensor was designed, built and tested with a focus on the qualitative capabilities of EAP membranes as sensors. Experimental measurements were conducted that demonstrated the capability of the sensor to output a voltage signal proportional to a changing pressure. Several undesirable characteristics were observed during these initial tests such as strong hysteresis, non-linearity, very limited pressure range, and low fatigue life. A second generation prototype was then designed to remove or compensate for these undesirable characteristics. This prototype was then built and tested. The new design showed an almost complete removal of hysteretic non-linear effects and was capable of operating at 10 × the pressure range of the initial generation. This new design is the framework for a novel DEAP based pressure sensor ready for commercial applications.

An active valve incorporated into a microchip using a high strain electroactive polymer

Recently, various kinds of microvalves have been developed in the field of micro total analysis systems. Most are pneumatic or piezo electric valves, which require significant space on a microchip and hence make the system complicated. This study reports the use of an electroactive polymer-based microvalve that occupies only a small space on a microchip. An electroactive polymer membrane sandwiched between soft electrode sheets was placed on a dome-shaped diaphragm. The polymer actuator was installed in a glass microchip and the valve function was demonstrated. First, the displacement of the diaphragm was measured without fluid, and sufficient displacement (over 50μm) was obtained for valve closing. Second, flow in a linear microchannel was stopped and then restarted by the valve. The flow in the microchannel produced by the constant pressure from a microfluidic controller (1.0kPa) was completely stopped by applying a 50V/μm electric field. This valve functioned well at pressures up to 4.0kPa. The response time was about 0.7s, similar to the time required for piezo electric actuator valves in channels of this size. This type of valve is very suitable for portable devices filed because of its compactness.

Inkjet Printed Structures for Smart Lab-on-Chip Systems

Lab-on-Chip microfluidic systems require onboard functionalities such as fluid pumping, heating and fluorescent or chemical sensing. An approach is presented to realize these structures by inkjet printing of functional materials or material sandwiches and subsequent curing or sintering. In detail an electro-active polymer membrane pump with passive microstructured valves, an open loop controlled ohmic heater structure for maintaining discrete fluid temperatures and electrodes for free-flow isoelectric focusing along with fluorescent hydrogel pads for pH sensing are discussed that all together are printed onto the cover foil of a polymer based microfluidic chip platform at the size of a microscope slide.

Equivalent circuit modeling of ionomer and ionic polymer conductive network composite actuators containing ionic liquids

In this study, we demonstrate electrical equivalent circuits that model the complex frequency-dependent impedance of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-Tf) containing electro-active polymer membranes and ionic polymer conductor network composite (IPCNC) devices. The devices include Nafion membrane actuators, Nafion coated with layer-by-layer (LbL) Au nanoparticle/poly(allylamine hydrochloride) (PAH) composite actuators, and Nafion with vertically aligned carbon nanotube (VA-CNT)/Nafion composite actuators. It is found that the low frequency responses of these devices indicate Warburg diffusion. Therefore, Warburg impedance is utilized to model the low frequency diffusion behavior of the devices, while the electric double layer capacitance (Cdl) represents the storage of drifting ions under electric field at high frequencies. It is found that Cdl for Nafion with 40wt% EMI-Tf is 7.5μF/cm2 and increases to 11.4μF/cm2 with increasing surface area of the LbL composite electrode. Cdl increases further to above 3×103μF/cm2 for an actuator with 12μm VA-CNT/Nafion composite electrodes, while the Warburg coefficient AW remains nearly the same for all the devices. As a result, the actuation magnitude and speed increase with charges accumulated due to higher Cdl, without much increase in the contribution from the slow ion diffusion process.

Energy harvesting using ionic electro-active polymer thin films with Ag-basedelectrodes

In this paper we employ the phenomenon of bending deformation induced transport ofcations via the polymer chains in the thickness direction of an electro-active polymer(EAP)–metal composite thin film for mechanical energy harvesting. While EAPs have beenapplied in the past in actuators and artificial muscles, promising applications of suchmaterials in hydrodynamic and vibratory energy harvesting are reported in this paper. Forthis, functionalization of EAPs with metal electrodes is the key factor in improving theenergy harvesting efficiency. Unlike Pt-based electrodes, Ag-based electrodes havebeen deposited on an EAP membrane made of Nafion. The developed ionic metalpolymer composite (IPMC) membrane is subjected to a dynamic bending load,hydrodynamically, and evaluated for the voltage generated against an externalelectrical load. An increase of a few orders of magnitude has been observed in theharvested energy density and power density in air, deionized water and in electrolytesolutions with varying concentrations of sodium chloride (NaCl) as compared toPt-based IPMC performances reported in the published literature. This will havepotential applications in hydrodynamic and residual environmental energy harvestingto power sensors and actuators based on micro-and nano-electro-mechanicalsystems (MEMS and NEMS) for biomedical, aerospace and oceanic applications.

Thermo-Magnetic, Piezo-Electric and Electroactive Energy Harvesting Devices

AbstractWe present three approaches to harvesting ambient energy, based on complementary physical effects in order to exploit three kinds of energy available for harvesting:Mechanical vibrationsMechanical vibration energy can be harvested with resonant mechanical structures excited by the vibrations; this scavenged energy is then transformed into electricity by piezoelectric materials. We propose to use thin piezoelectric layers deposited on the resonant structure.An on-chip integrated prototype, using a seismic mass at the end of a Si cantilever beam coated with a piezoelectric AlN film (overall volume 5 mm3), produces 30 nW of rectified power at 3 V under 0.4 g acceleration, which is enough to power a wireless sensor. Power conditioning electronics adapted to ultra-low voltage input is also proposed, which can efficiently charge a storage capacitor under very low accelerations. The fully micro-fabricated System on a Package combines a MEMS generator and ASIC power management circuit.Evolutions of ambient temperatureA permanent magnet is attached to a PZT/brass bimorph, and placed near a "thermo-magnetic" material (FeNi) which Curie temperature can be tuned around the ambient. During slow cooling or heating by the ambient air, the FeNi magnetic properties vary slowly and thus the attraction force between the FeNi and the NdFeB magnet varies slowly. Despite the slow global evolutions, the opposition between the linearity of the bimorph bending and the strong non-linearity of the magnetic attraction over distance leads to brutal clamping or release of the magnet around Tc: the piezo can then efficiently convert these fast deformations into electricity. Operational temperature range can be set by tuning the FeNi composition to obtain a predefined Curie point; hysteresis between the cooling/heating thresholds can be tuned by modifying the gap between the magnet and the FeNi.The cm-scale prototype generates a peak voltage of 35 V on release (T &gt; Tc). For a discharge time of 0.1 s through a 1 MΩ load, the total energy harvested is 13.5 μJ per stroke, i.e. 1.35 mW of average power (respectively -14 V, 2.2 μJ and 0.22 mW on clamping when T &lt; Tc). Output power is surprisingly constant for various load values tested. Scaling effects must now be addressed to assess the feasibility of an integrated MEMS generator and its potential efficiency.Low-frequency, large amplitude bending from human motion:A very light, flexible electro-active polymer membrane (50 x 30 mm, 31 μm thick) operates in a large frequency spectrum from quasi-static to dynamic range. It scavenges 0.1 mJ per cycle at 1 Hz, under 170 V and constant charge Q: 100 μW is enough to supply a low-power system.Improvements under investigation include achieving poling voltage with piezoelectric polymer or electrets polymer, using multi-stack scavengers to miniaturize the structure and to decrease the poling voltage V, and integration into textile.