Ionic Polymer Metal Composite Samples Research Articles

Response Surface Modelling Nafion-117 Sorption of Tetraammineplatinum(II) Chloride in the Electroless Plating of IPMCs.

This work looks at the effects of a varying concentration, soak time, pH and temperature on the sorption of tetraammineplatinum(II) chloride (Pt-Ammine) in Nafion-117 films in the context of the electroless plating of ionic polymer-metal composites (IPMCs). Sorption is characterised by atomic absorption spectroscopy. A definitive screening design carried out determined all four factors to be significant for further analysis using response surface modelling. A duplicated central composite design (CCD) was utilised to characterise how the four factors affect the sorption amount and efficiency. Regression models for both responses were of poor fit. Nevertheless, key insights were obtained on the effects of the process parameters on sorption behaviour. The results indicate that above 0.5 g/L Pt-Ammine sorption, the platinisation of 10 × 50 mm IPMC samples through sodium borohydride reduction becomes redundant by the surface resistance metric. IPMCs with surface resistance values of approximately 2.5 Ω/square were obtained through only one round of chemical reduction. Varying surface morphologies and electrode thicknesses were analysed under a scanning electron microscope. The CCD parameter settings were validated. Recommended settings for optimised Pt-Ammine sorption in 10 × 50 mm Nafion-117 films were identified as follows: 1.0 g/L Pt-Ammine concentration, 24 h soak time, pH of 3 and temperature of 20 °C.

Manufacturing thin ionic polymer metal composite for sensing at the microscale

Ionic polymer metal composites (IPMCs) are a class of materials with a rising appeal in biological micro-electromechanical systems (bio-MEMS) due to their unique properties (low voltage output, bio-compatibility, affinity with ionic medium). While tailoring and improving actuation capabilities of IPMCs is a key motivator in almost all IPMC manufacturing reports, very little efforts have been dedicated to sensing using IPMC thinner than 100 µm. Most reports on IPMC manufacturing and utilization rely on 180 µm-thick Nafion with platinum electrodes, too stiff for bio-MEMS applications. The same fabrication process on thinner membranes does yield in very poor electrodes and performance, and needs to be studied to increase flexibility and sensitivity in the microscale range. This study demonstrates an electroless Pt deposition method for fabricating bio-MEMS-suitable 50 µm-thick IPMC samples. First, we perform a comparative study on the platinum distribution within the Nafion backbone as well as on the surface for the standard electroless deposition recipe for thin (50 µm) and thick (180 µm) Nafion. We report strong differences in platinum distribution for thick and thin IPMC that experienced the same manufacturing process. By varying chemical concentrations from the standard recipe we obtain convenient platinum distribution on thin Nafion, with platinum mainly localized in proximity of surface, as well as electrodes with lower sheet resistance. We could measure the flexural rigidity as N·m2, 46 times lower than standard 180 µm-thick IPMC. The calculated sensitivity is 0.476 ± 0.02 mV mm−1 and the limit of detection for our sensor is 500 ± 20 µm. This procedure sets a milestone for manufacturing 50 µm-thick IPMC for transducers and sensors in bio-MEMS applications.

Hierarchical Structure Fabrication of IPMC Strain Sensor With High Sensitivity

In this paper, a biological template method is introduced and investigated to fabricate ionic polymer-metal composite (IPMC) strain sensor with bionic hierarchical structures. We utilized the multi-level structure of reed leaf surface, which can improve the contact area between the substrate and the electrode layers. Hierarchical structures were observed on the IPMC samples, including pyramid strips with the width in the range of 60–80 μm as well as synaptic scatters with diameter around 10 μm. In addition, five kinds of sensors with different interface structures were obtained by combining the traditional microneedle roller roughening and chemical plating processes. It was found that the IPMC sensor with reed-leaf and microneedle structure on each side presented the best performance, along with a high linearity, a sensitivity of 62.5 mV/1% and a large generated voltage peak under given mechanical stimuli, which is 3.7 times that of the sample fabricated without roughening.

Preparation and performance analysis of Pt-IPMC for driving bionic tulip

Based on the biological characteristics of tulip, the low driving voltage and fast response of ionic polymer metal composite (IPMC), we analyzed the fabrication, morphology and performance of the platinum IPMC (Pt-IPMC) and selected the right IPMC for driving bionic tulip. The preparation and performance of IPMC was analyzed first in this paper such as blocking force, output displacement and bending angle of IPMC under the different directed current voltage (DC). The optimal IPMC sample size and driving voltage were selected based on tulip blooming angles and the strain energy density of IPMC, which completed the blooming process of bionic tulip. The feasibility of IPMC used in driving bionic field was fully proved in this paper, which laid a foundation for the application of IPMC in driving biomimetic biological robots.

Analysis on enhancing the sensing behavior of ionic polymer metal composite based sensors

In this paper, an in-depth analysis of IPMC (ionic polymer metal composite) as sensors is performed, motivated by application to flapping wing micro air vehicles. The effect of water uptake for different IPMC samples reveals a correlation between IPMC metal content and water uptake. The effect of introducing a mass to the end of High-frequency IPMC (HFI ∼ 20.9 Hz) sensor shows an improvement in the IPMC sensing behavior, whereas, for the Low-frequency IPMC (LFI ∼ 8.9 Hz) sensor, there is a reverse trend. Gold (Au) coating on an HFI sensor results in a decrease in resonant frequency. Different mass loaded on the Au coated HFI beams reveals that the pre-bending by adding end mass to HFI sensor is beneficial up to a specific mass level, after which the sensing voltage decreases. The optimized mass loading for the Au coated HFI is determined.

Displacement response of ionic polymer metal composite actuator to asymmetric square waves in air operating

Ionic Polymer Metal Composite (IPMC) is a novel electrical actuated intelligent material with the advantages of low driving voltage, large bending displacement, high flexibility, low density and so on. It has been used as an intelligent driving material with prospective applications for robot fish and bionic organ, and is expected to be used out of water. As an important and applicable characteristic, displacement response of IPMC has drawn tons of researchers’ attentions. In this paper, the asymmetric square waves with variable frequencies, low level voltages, and duty cycles were employed to drive IPMC samples, the displacement responses were investigated and analyzed. The control mode of IPMC sample was obtained using curve fitting of step response. By combining Bode plot of IPMC system with the Fourier transform of square waves, the effect of parameters changes to the displacement response were analyzed and discussed, and the potential application of the asymmetric displacement is illustrated and proposed by a capsule like underwater robot.

Harvesting Energy From an Ionic Polymer–Metal Composite in a Steady Air Flow

Abstract The paper presents the results of an investigation of a possibility for energy harvesting from a flexible material such as an ionic polymer–metal composite (IPMC) placed in a steady flow of air characteristic of conditions typical to a densely urbanized area. As electro-active devices require dynamic loading to produce current, their response is usually evaluated in unsteady and turbulent flows, where an electro-active polymer follows the movement of the medium surrounding the device. In our study, we examine the flow conditions at which flutter sets the IPMC strip in motion. Although flutter is often perceived as an unfavorable phenomenon for aerodynamic applications and civil structures, it may be beneficial for harvesting wind energy. Of particular interest is that this phenomenon may occur in a steady flow, which potentially expands the range of favorable flow conditions for energy harvesting. In the paper, the air speed at which flutter occurs and the speed range at which flutter is sustained are provided along with the estimated amount of power produced in an IPMC sample of specified dimensions.

An investigation of multimodal sensing capabilities of ionic polymer-metal composites

This paper presents the novel multimodal sensing capabilities of ionic polymer metal composites (IPMCs) for measuring linear and rotational deformations. Two IPMC samples with Gold (Au) and black Platinum (Pt) electrodes were manufactured, and their responses under twisting and axial compression/tension were investigated. To perform consistent and rigorous experiments to study the multimodal sensing capabilities of the IPMC samples, an experimental test bed was developed that enabled the application of twisting, axial compression, and axial tension to the IPMC strips both in a separate and combined manner, while recording their generated voltage responses. Through rigorous experiments, this study demonstrates the unique sensing capabilities of IPMCs to create distributed nanosensing over the entire body of the IPMC sample. Upon various types of deformations, IPMCs were shown to generate unique and distinct output voltage signals that were highly correlated with the type of motions induced. In particular, the strongest correlations of more than 0.9 were found between the IPMCs’ responses and the applied mechanical stimuli in the twisting and axial compression modes, while moderate correlations were observed in the axial tension mode. These results provide a proof-of-concept for the future use of IPMCs as flexible and versatile sensors for measuring linear and rotational motions in applications such as wearable soft robotics.

Sensing and Self-Sensing Actuation Methods for Ionic Polymer–Metal Composite (IPMC): A Review

Ionic polymer–metal composites (IPMC) are smart material transducers that bend in response to low-voltage stimuli and generate voltage in response to bending. IPMCs are mechanically compliant, simple in construction, and easy to cut into desired shape. This allows the designing of novel sensing and actuation systems, e.g., for soft and bio-inspired robotics. IPMC sensing can be implemented in multiple ways, resulting in significantly different sensing characteristics. This paper will review the methods and research efforts to use IPMCs as deformation sensors. We will address efforts to model the IPMC sensing phenomenon, and implementation and characteristics of different IPMC sensing methods. Proposed sensing methods are divided into active sensing, passive sensing, and self-sensing actuation (SSA), whereas the active sensing methods measure one of IPMC-generated voltage, charge, or current; passive methods measure variations in IPMC impedances, or use it in capacitive sensor element circuit, and SSA methods implement simultaneous sensing and actuation on the same IPMC sample. Frequency ranges for reliable sensing vary among the methods, and no single method has been demonstrated to be effective for sensing in the full spectrum of IPMC actuation capabilities, i.e., from DC to ∼100 Hz. However, this limitation can be overcome by combining several sensing methods.

A Gradient Model for Young’s Modulus and Surface Electrode Resistance of Ionic Polymer–Metal Composite

A new model is proposed to estimate Young’s modulus and surface electrode resistance of the ionic polymer–metal composite (IPMC) with a gradient distribution of microstructure. The entire IPMC electrode is divided into two parts, i.e., the porous metal electrode and the gradient polymer–metal composite electrode, according to the geometric properties of the electroless plated metal electrode. The validity and accuracy of the model are justified by comparing with the experimental observations of IPMC samples. The differences between model predictions and experimental data of Young’s modulus and surface resistance of IPMC samples are +6.8% and –5.5%, respectively, indicating a reasonably good agreement.

The Effects of Dimensions on the Deformation Sensing Performance of Ionic Polymer-Metal Composites.

As an excellent transducer, ionic polymer-metal composites (IPMCs) can act as both an actuator and a sensor. During its sensing process, many factors, such as the water content, the cation type, the surface electrode, and the dimensions of the IPMC sample, have a considerable impact on the IPMC sensing performance. In this paper, the effect of dimensions focused on the Pd-Au typed IPMC samples with various thicknesses, widths, and lengths that were fabricated and their deformation sensing performances were tested and estimated using a self-made electromechanical sensing platform. In our experiments, we employed a two-sensing mode (both current and voltage) to record the signals generated by the IPMC bending. By comparison, it was found that the response trend was closer to the applied deformation curve using the voltage-sensing mode. The following conclusions were obtained. As the thickness increased, IPMC exhibited a better deformation-sensing performance. The thickness of the sample changed from 50 μm to 500 μm and corresponded to a voltage response signal from 0.3 to 1.6 mV. On the contrary, as the length increased, the sensing performance of IPMC decreased when subjected to equal bending. The width displayed a weaker effect on the sensing response. In order to obtain a stronger sensing response, a thickness increase, together with a length reduction, of the IPMC sample is a feasible way. Also, a simplified static model was proposed to successfully explain the sensing properties of IPMC with various sizes.

Influence of Humidity and Actuation time on Electromechanical Characteristics of Ionic Polymer-Metal Composite Actuators

This paper experimentally investigates the effects of humidity and actuation time on the electromechanical properties of Ionic Polymer-Metal Composites (IPMC) to improve the practical applications of using the IPMCs as soft biomimetic sensors and actuators. The experiments are conducted in both the open atmosphere (uncontrolled environment at room temperature) and inside a controlled environmental chamber under different input voltages (in term of wave shape, value, and frequency). Results show that the IPMC’s electromechanical properties, namely the deformation capacity and electrical resistance, highly depend on the water content (in the IPMC strip and environment) and the duration of actuation. The Deflection and current of the tested IPMC samples can be represented by an exponential time function were an exponent value decreases with increasing the humidity. IPMC deformation capacity decreases while material electrical resistance increases during activation session. Increasing relative humidity to more than 50% reduces the drying effect on the IPMC deformation capacity and resistance. Also, the IPMC material shows a relaxation behavior for a step voltage input, which can be related to the back immigration of the hydrated cations from the anode to the cathode due to higher pressure at the anode side of the IPMC strip.

Theoretical and experimental investigation of the shape memory properties of an ionic polymer–metal composite

An ionic polymer–metal composite (IPMC) is typically based on a Nafion membrane with electrode plating on both sides and has a promising potential for biomimetic robotics, biomedical devices and human affinity applications. In this paper, the shape memory properties of IPMC were theoretically and experimentally studied. We presented the multiple shape memory properties of a Nafion cylinder. A physics based model of the IPMC was proposed. The free energy density theory was utilized to analyze the shape properties of the IPMC. To verify the model, IPMC samples with Nafion as the base membrane were prepared and experiments were conducted. A simulation of the model was performed and the results were compared with the experimental data. It was successfully demonstrated that the theoretical model can well explain the shape memory properties of the IPMC. The results showed that the reheat glass transition temperature of the IPMC is lower than the programming temperature. It was also found that the back-relaxation of the IPMC decreases as the programming temperature increases. The current study may be useful in order to better understand the shape memory effect of IPMC.

Experimental study and electromechanical model analysis of the nonlinear deformation behavior of IPMC actuators

This paper develops analytical electromechanical formulas to predict the mechanical deformation of ionic polymer–metal composite (IPMC) cantilever actuators under DC excitation voltages. In this research, IPMC samples with Pt and Ag electrodes were manufactured, and the large nonlinear deformation and the effect of curvature on surface electrode resistance of the IPMC samples were investigated experimentally and theoretically. A distributed electrical model was modified for calculating the distribution of voltage along the bending actuator. Then an irreversible thermodynamic model that could predict the curvature of a unit part of an IPMC actuator is combined with the electrical model so that an analytical electromechanical model is developed. The electromechanical model is then validated against the experimental results obtained from Pt- and Ag-IPMC actuators under various excitation voltages. The good agreement between the electromechanical model and the actuators shows that the analytical electromechanical model can accurately describe the large nonlinear quasi-static deflection behavior of IPMC actuators.

Effects of cation on electrical responses of ionic polymer-metal composite sensors at various ambient humidities

In this study, we investigated the effects of various cations on the electrical responses of ionic polymer–metal composite (IPMC) sensors at various ambient humidities. Four typical Au–Nafion IPMC samples were prepared with H+, Li+, Na+, and K+ cations. The voltage and current responses of the IPMCs were investigated under static and dynamic bending displacements. The orders of the voltage and current amplitudes were generally Li+ > Na+ > K+ > H+ and depended on the cation transport properties and the water content. The static voltage response first increased to a peak and then slowly decreased to a steady state. A negative steady-state voltage was initially observed for the IPMC with H+ cations under near saturation conditions. The voltage amplitude increased monotonously with increasing frequency from 0.1 to 10 Hz at a high relative humidity (RH, ∼90%), first increased and then decreased at moderate humidity (RH, ∼50%), and decreased continuously at low humidity (RH, ∼20%). The static current response first rapidly increased to a peak and then quickly decayed. During current decay, free oscillation decay occurred at high humidity and attenuated with decreasing humidity. This was confirmed to be the result of cation movement in the IPMC. There are three necessary conditions for oscillation: sufficient migrated cations, high cation mobility, and high stiffness of the polymer network. For the dynamic current response, the amplitude increased with increasing frequency (0.1–10 Hz) and showed good linearity. The underlying physics, mainly involving cation forward migration and back diffusion caused by mechano-chemo-electrical coupling, was clarified.

An external disturbance sensor for ionic polymer metal composite actuators

Ionic polymer metal composite (IPMC) is a fast-growing type of smart material with a wide range of applications. IPMC has been used extensively as an actuator, but for effective usage, one must add a self-sensing ability to it. Two common self-sensing techniques are mechanical-to-electrical transducer and surface resistance. The first one cannot be used while the actuator is running, and the second one needs a sample modification. In this work, we present a new self-sensing method, which can measure external disturbance in the presence of actuator voltage without any sample modification. The resistance across an IPMC sample follows Ohm’s law at sufficiently high frequency. We exploit the frequency dependency of the resistance across the sample to design the self-sensing method. In this technique a function generator, a lock-in amplifier and an isolation circuit were employed to measure an external impulse or steady disturbance. As implementing this technique does not require any change to the IPMC specimen or electrical connection (hanger), it can be added to any existing electroactive device.

A comprehensive physics-based model encompassing variable surface resistance and underlying physics of ionic polymer-metal composite actuators

The ionic polymer-metal composite (IPMC) is an emerging smart material in actuation and sensing applications, such as artificial muscles, underwater actuators, and advanced medical devices. However, the effect of the change in surface electrode properties on the actuating of IPMC has not been well studied. To address this problem, we theoretically predict and experimentally investigate the dynamic electro-mechanical response of the IPMC thin-strip actuator. A model of the IPMC actuator is proposed based on the Poisson-Nernst-Planck equations for ion transport and charge dynamics in the polymer membrane, while a physical model for the change of surface resistance of the electrodes of the IPMC due to deformation is also incorporated. By incorporating these two models, a complete, dynamic, physics-based model for IPMC actuators is presented. To verify the model, IPMC samples were prepared and experiments were conducted. The results show that the theoretical model can accurately predict the actuating performance of IPMC actuators over a range of dynamic conditions. Additionally, the charge dynamics inside the polymer during the oscillation of the IPMC is presented. It is also shown that the charge at the boundary mainly affects the induced stress of the IPMC. The current study is beneficial for the comprehensive understanding of the surface electrode effect on the performance of IPMC actuators.

Investigation into the actuating properties of ionic polymer metal composites using various electrolytes

With an increasing trend of ionic polymer metal composites (IPMC) applied in marine system surrounding with abundant K+ and Na+ ions, efforts of IPMC with different electrolytes on actuating properties were investigated. In this paper, different IPMC were prepared using Li+, Na+, and K+ as the electrolyte cations and water, ionic liquid, and ethylene glycol as the electrolyte solvent. Actuating parameters were measured based on a customized experimental setup under dynamic voltage and dynamic frequency. Results showed that electrolyte solvent can affect the working life cycle and displacement of IPMC under dynamic voltage and frequency signal, whereas the electrolyte cations can only influence the actuating properties under dynamic voltage. An initial increase in the strain rate of all IPMC samples was discovered following a decrease. Furthermore, it is visible from the results analysis that each group of IPMC had a constant solvent absorption content, although they obtained different contents of electrolyte solvent and cations. Moreover, a principle was observed in the voltage tolerance of IPMC with Li+, Na+, and K+ as increasing atomic weigh of electrolyte cations. In addition, a relationship between actuating properties and electrolytes was illuminated in this paper.

Electrical impedance controls mechanical sensing in ionic polymer metal composites

Ionic polymer metal composites (IPMCs) are a class of soft electroactive materials that are recently finding extensive application as mechanical sensors and energy harvesters in liquids. In their most fundamental form, IPMCs are composed of a hydrated ionomeric membrane that is sandwiched between two electrochemically deposited metal electrodes. Ionomer swelling, counterion diffusion, and the formation of electric double layers are some of the physical phenomena underpinning energy transduction in IPMCs; however, a thorough understanding of the relative influence of such phenomena is yet to be established. Here, we propose a physics-based modeling framework, based on the Poisson-Nernst-Planck system, to describe IPMC chemoelectrical response to an imposed time-varying flexural deformation. We utilize the method of matched asymptotic expansions to compute a closed-form solution for the electric potential and counterion concentration in the IPMC. The model predicts that IPMC sensing is independent of the time rate of deformation and linearly correlated to the mechanical curvature, with a coefficient of proportionality that is a function of the ionomer thickness and the temperature. Thus, our results demonstrate that the characterization of IPMC electrical impedance suffices to identify all the parameters that are relevant to sensing, in contrast with the current state of knowledge. Theoretical results are validated through experiments on patterned in-house fabricated IPMC samples that are subject to time-varying flexural deformations.

Improving the performance of IPMCs with a gradient in thickness

An ionic polymer metal composite (IPMC) is a kind of electro-active polymer. Due to the properties of low driving voltage, large deformation, flexibility and lightness, it is becoming one of the more popular from a diversity of smart materials. In this study, a novel structure of Nafion® film is proposed to improve the performance of an IPMC. IPMC samples with a gradient structure in thickness are fabricated and their performance is investigated to confirm the validity of the gradient structure. The deformation displacement and the blocking force are compared under AC and DC voltage by experiments. The results indicate that the structure of gradient in thickness would improve the performance both in deformation displacement and blocking force.