Nafion-based Ionic Polymer-metal Composites Research Articles

Ionic Polymer Metal Composite Based Smart Tongue Using Machine Learning

Ionic polymer metal composite (IPMC)-based new type of taste sensing technology is focused on this study. The developed sensor can sense five taste senses (salty, sweetness, spicy, bitterness, and sourness) artificially. Development of electronic tongue using Nafion-based IPMC strip (Pt-electroded) is the background philosophy for the current finding. Due to the hydrophilic nature of the perfluorinated polymer membrane, IPMC strips while immersed into test solutions, cations like Li <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> , Na <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> , K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> , H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> , etc., diffused into the polymer layer penetrating through the Pt-electrode surface of the IPMC and rearranged inside the polymer matrix. Bending of IPMC strip produces a small potential difference in millivolt (mV), which is developed across two Pt-electroded sides of IPMC. The output voltage across two electrode sides of IPMC for different taste samples of different concentration shows distinct voltage pattern and is measured in terms of potential difference across the Pt-electrode of IPMC. K-nearest neighbor classification approach of machine learning is useful for the identification of unknown taste agents. The average performance index of the developed machine learning model for the prediction of basic taste is 93.45%. Due to the nontoxic nature of IPMC, taste identification of different food contents would be feasible using this sensing technology.

Fabrication of a multilayered SGO/macroporous Nafion-based IPMC with enhanced actuation performance

Ionic polymer-metal composites (IPMCs) composed of Nafion film and platinum deposited on both faces have gained much attention in biomedical engineering as actuators because it can show large bending motion under an electric field. This study focuses on the design of a multilayered IPMC actuator based on sulfonated graphene oxide (SGO) modified macroporous Nafion film. The Nafion film is firstly fabricated via templating technique by using silica spheres as template and SGO as a conductive agent dispersed in Nafion film. Then, Pt nanoparticles are deposited on both faces of the as-prepared Nafion film to fabricate the actuator (denoted as IPMC-SGO-M). In the IPMC-SGO-M, macropores and SGO co-exist in the Nafion film, which can effectively enhance the rapid transport of ions and electrons. In addition, small Pt nanoparticles are uniformly dispersed on the surface of the Nafion film, which can improve the water-uptake capability and charge redistribution between two layers of electrode regions. As a result, the tip displacements of the IPMC-SGO-M are 1.7-fold and 1.9-fold higher than that of the IPMC based on macroporous Nafion film (IPMC-M) under 6.2 and 6.6 V, respectively. The blocking forces of the IPMC-SGO-M are about 2.6-fold and 2.3-fold higher than that of IPMC-M under 6.2 and 6.6 V, respectively.

Coupled electro-chemo-elasticity: Application to modeling the actuation response of ionic polymer–metal composites

We have formulated a large deformation thermodynamically-consistent electro-chemo-elasticity theory for modeling the actuation response of ionic polymer–metal composites. Our theory accounts for the simultaneous evolution of the electric potential, the concentration of the mobile hydrated cations, and the deformation of the host ionic polymer matrix. We have numerically implemented our theory in an implicit finite element program. We use this simulation capability to first calibrate the material parameters in the theory for a Nafion-based ionic polymer–metal composite, and then validate our theory by comparing predictions from the theory against other experimental data available in the literature. We also demonstrate the utility of our simulation capability by conducting full three-dimensional simulations of two soft-robotics applications with some geometric complexity: (i) a biomimetic fin, and (ii) a micro-gripper.

Energy Harvesting of Ionic Polymer-Metal Composites Based on Microcellular Foamed Nafion in Aqueous Environment

The purpose of this study was to determine how to improve the energy-harvesting properties of polymer electrolyte membranes by varying their porosity. We achieved this by applying microcellular foaming process (MCP) to Nafion-based ionic polymer–metal composites (IPMCs). We manufactured an IPMC by forming a Pt electrode through an electroless plating method on the Nafion film, to which porosity was imparted by varying the foaming ratio and inducing deformation by vibrating the specimen using a prototype device that we developed ourselves. We attempted to harvest energy via fluid flow that occurred owing to displacement movement. When the Nafion film was foamed at a temperature of 140 °C or higher, it was observed that cells with size of approximately 1 µm or more were formed, and when the saturation temperature was lowered, a denser and larger number of cells were formed. Moreover, the cells formed on the electrolyte membrane allowed the retention of more water. Water retention generated charges contributed to the operational stability of IPMC. This was attributed to the difference in the amount of charge generated by changing only the internal morphology of the electrolyte membrane, without changing the substrate or the electrode material.

Electrochemical viscoelastic modeling to predict quasi-static and dynamic response of IPMC actuators

A nonlinear dynamic viscoelastic model of an ionic polymer metal composite (IPMC) actuator is presented based on the viscoelastic constitutive equations and an energy-based variational approach to acquire dynamic and quasi-static response. For this purpose, the equation of motion of an IPMC actuator is obtained by considering the actuator as a cantilever viscoelastic beam and utlizing continuum mechanic relations, Euler-Bernoulli beam theory, Hamilton's principle, and electrochemical properties of ionomer. This new model can simulate time-dependent tip displacement of the IPMC actuators and predict the back-relaxation that occurs in the Nafion-based IPMC actuator under an imposed step voltage. The transfer function derived from the proposed model provides a good frequency response prediction in comparison to the experimental results.This model also can be utilized to obtain mechanical response and vibration analysis of the IPMC sensors.

Structure-Property Relationships in Hybrid Cellulose Nanofibrils/Nafion-Based Ionic Polymer-Metal Composites.

Herein, we report the production of ionic polymer-metal composites (IPMCs) hybridized with cellulose nanofibrils (CNF) as a partial substitute for Nafion®. The aim is not only to reduce the production cost and enhance respective mechanical/thermal properties but also to bestow a considerable degree of biodegradability to such products. Formulations with different CNF/Nafion® ratios were produced in a thin-film casting process. Crack-free films were air-dried and plated by platinum (Pt) through an oxidation-reduction reaction. The produced hybrids were analyzed in terms of thermal stability, mechanical and morphological aspects to examine their performance compared to the Nafion-based IPMC prior to plating process. Results indicated that films with higher CNF loadings had improved tensile strengths and elastic moduli but reduced ductility. Thermogravimetric analysis (TGA) showed that the incorporation of CNF to the matrix reduced its thermal stability almost linearly, however, the onset of decomposition point remained above 120 °C, which was far above the temperature the composite membrane is expected to be exposed to. The addition of a cross-linking agent to the formulations helped with maintaining the integrity of the membranes during the plating process, thereby improving surface conductivity. The focus of the current study was on the physical and morphological properties of the films, and the presented data advocate the potential utilization of CNF as a nontoxic and sustainable bio-polymer for blending with perfluorosulfonic acid-based co-polymers, such as Nafion®, to be used in electroactive membranes.

Advances in Polymeric Materials for Electromechanical Devices.

Electroactive polymers (EAP) provide lightweight and cost-effective materials that enable the next generation of electromechanical devices. Commercial polymers have historically dominated research in EAP devices due to their availability. However, several drawbacks of these materials have limited their commercial applications, necessitating new materials for the commercial success of future EAP devices. This review highlights recent advances in novel EAPs for ionic polymer-metal composites (IPMC) and dielectric elastomer actuators (DEA). Ion-containing block copolymers and charged segmented condensation polymers demonstrate suitable electromechanical properties competitive with Nafion-based IPMCs. In addition, swelling ionic polymer membranes with free ionic liquid enhances ionic conductivity and promotes electromechanical actuation. Synthetic approaches to increasing permittivity in dielectric elastomers are also explored as a method of producing more efficient DEAs. Incorporating polar functional groups into siloxane and acrylic elastomers through grafting or blending provides high-dielectric elastomers for use in DEAs with low driving voltages.

From modeling to implementation of a method for restraining back relaxation in ionic polymer–metal composite soft actuators

Ionic polymer–metal composites are an emerging kind of electroactive polymer actuators, which can bend in response to a relatively low driving voltage. However, to enhance the actuation performance of ionic polymer–metal composites, some of their drawbacks should be considered. One of the most important drawbacks is “back relaxation.” The so-called back relaxation effect means, when a step input voltage is applied to the ionic polymer–metal composite, the conventional bending displacement toward the anode is followed by an unwanted and slow back relaxation toward the cathode. Control-based methods for restraining the ionic polymer–metal composite back relaxation effect are feedback-based schemes which apply significant constraints to dominant applications of ionic polymer–metal composite actuators especially in biomedical applications. In this article, we present an entirely scientific-based mathematical modeling to achieve a practical method for restraining the back relaxation effect in Nafion-based ionic polymer–metal composites, relying on creating a specific pattern on Pt layers of the ionic polymer–metal composites and applying a local Gaussian disturbance to this patterned ionic polymer–metal composites.

Searching for a new ionomer for 3D printable ionic polymer–metal composites: Aquivion as a candidate

The work presented in this paper introduces Aquivion as a potential candidate for additive manufacturing of ionomeric polymers for the application of IPMCs. First, Aquivion was characterized and compared with Nafion to show that it has the similar qualities, with the major difference being the ionic conductivity. Ionic polymer–metal composites (IPMCs) were fabricated using off-the-shelf membranes of Nafion and Aquivion. The actuation tests showed improved performance for an IPMC with Aquivion as the base compared to an IPMC with a Nafion base. With these results in mind, additive manufacturing of unique shapes using Aquivion filament was studied. A 3D printer was modified to work with Aquivion filament and the polymer was printed into various shapes. Using the printed membranes, IPMCs were fabricated using an electroless plating process. Nafion-based and printed Aquivion-based IPMCs were tested for their performance in back relaxation, frequency driven actuation, blocking force, and mechano-electric sensing. The printed Aquivion-based IPMCs performed comparably to Nafion-based IPMC in back relaxation and showed significantly improved performance in frequency driven actuation, blocking force generation, and mechano-electric sensing.

Replacement of surface roughening using polyvinyl alcohol coating in the fabrication of nafion-based ionic polymer metal composite (IPMC) actuators

In this paper, we propose a new fabrication method for ionic polymer metal composite (IPMC) actuators using a Nafion/Polyvinyl alcohol layer coating instead of conventional surface roughening (sandblasting) to achieve good adhesion of a Pt electrode. Compared with the Nafion membrane, the proposed membranes (NNP25 and NNP50) have increased mechanical properties (tensile strength and Young’s moduli). In addition, IPMCs using the proposed membranes had lower current densities than the Nafion-based IPMC. Therefore, compared with the Nafion-based IPMC, the proposed NNP25- and NNP50-based IPMCs had higher blocking forces, but lower tip displacements. Consequently, through the proposed simple procedure and cost-effective fabrication method using a Nafion/Polyvinyl alcohol layer coating, we can fabricate that the proposed IPMC actuators have enhanced mechanical properties in comparison with the sandblasting surface roughening used in the conventional IPMC fabrication method.

Voltage attenuation along the electrodes of ionic polymer metal composites

In this note, we study voltage attenuation along the electrodes of an ionic polymer metal composite. We conduct a series of experiments on an in-house fabricated Nafion-based ionic polymer metal composite, subject to different voltage inputs. We adapt a recently proposed physics-based distributed circuit model to elucidate voltage attenuation as a function of the distance along the ionic polymer metal composite and the frequency of the voltage input. The parameters of the distributed circuit model, including surface resistances and through-the-thickness impedance, are identified through independent experiments. Theoretical predictions are in good agreement with experimental observations, demonstrating the potential of the model to inform the design of sensors, actuators, and energy harvesters. Our results indicate that voltage attenuation is controlled by electric parameters associated with the electrode composition and morphology, which can both be adjusted during fabrication.

Fabrication of SGO/Nafion-based IPMC soft actuators with sea anemone-like Pt electrodes and enhanced actuation performance

In the current work, graphene oxide (GO) and sulfonated graphene oxide (SGO) were synthesized and composited with Nafion to increase the water uptake (WUP) and ion exchange capacity (IEC) of the cast membranes. Ionic polymer-metal composite (IPMC) soft actuators in protonated form were fabricated based on the cast pure Nafion, Nafion/GO and Nafion/SGO membranes. The effects of incorporating GO and SGO in IPMC actuators were followed using physicochemical, electrochemical and electromechanical measurements and were compared with the corresponding behavior of pure Nafion-based IPMC actuators. Morphology analysis of IPMCs showed effective incorporation of GO and SGO and clarified the dependency of Pt electrode structure on the SGO content of the Nafion membranes. The addition of SGO resulted in dramatic increases in the WUP, IEC and hydrated thickness of the Nafion membranes and also in the capacitance, ionic conduction and in the tip displacement of the IPMC actuators. The small tip displacement of pure Nafion-based actuator was enhanced by eight times by adding 1 wt% SGO. The results suggested that the dispersion of SGO throughout the continuous polymeric matrix significantly reduce water loss by increasing the obstructions within the Nafion membrane and also by formation of denser Pt grains in the electrode regions.

Terrestrial Walking Robot With 2DoF Ionic Polymer&amp;#x2013;Metal Composite (IPMC) Legs

This paper proposes a terrestrial walking robot using ionic polymer–metal composite (IPMC) actuators based on a poly-vinylidene fluoride (PVDF)/polyvinyl pyrrolidone (PVP)/polystyrene sulfuric acid (PSSA) blend membrane. The IPMC based on PVDF/PVP/PSSA with a polymer mixture ratio of 30/15/55 shows a higher tip displacement and greater blocking force than Nafion-based IPMC actuators at low dc voltages. An actuation model is developed for the proposed membrane-based IPMC actuators, representing the transfer function between the input applied voltage and the output displacement of the IPMC actuator. For the terrestrial walking robot, we use a two-degrees-of-freedom (2DoF) leg structure because of its superior characteristics in comparison with a 1DoF leg structure. In addition, a kinematic model of the 2DoF leg structure is introduced as a modeling framework based on the actuation model for the analysis of the locomotion using this IPMC leg structure. The simulation results of the actuation model and the kinematic model are compared with the empirical response of 1 and 2DoF legs. A terrestrial walking robot (size: $28\, {\rm mm} \times 18\, {\rm mm} \times 16.5$ mm, weight: 1.2 g) with two 2DoF IPMC legs and two dummy legs has been designed and fabricated. Finally, we demonstrate the walking motion of the terrestrial walking robot.

Enhanced ionic polymer metal composite actuator with porous nafion membrane using zinc oxide particulate leaching method

In this study, to improve the performance of an ionic polymer metal composite (IPMC), we suggest a porous nafion membrane fabricated with the particulate leaching method with zinc oxide and propose an IPMC that uses the porous nafion membrane. To fabricate this membrane, the proper ratio of nafion and zinc oxide powder is dispersed in a solvent. Then the zinc oxide embedded in the nafion membrane is fabricated with a casting method. With the particulate leaching method, the embedded zinc oxide particles are dissolved by an acid solution, and the spaces of the zinc oxide particles changed to pores. Finally, through electroless plating and ion exchange procedures, an IPMC with the porous nafion membrane is fabricated. The proposed IPMC has higher water uptake (WUP) and ion exchange capacity (IEC) and can show better actuation performance compared to the conventional nafion-based IPMC. We also measure the actuation displacement and blocking forces of the proposed IPMC. Compared with the conventional nafion-based IPMC, the proposed IPMC with the porous nafion membrane has increased displacements: about 80% at ac input and about 250% at dc input, and increased blocking force about 130% at dc input.

Ionic polymer-metal composite actuators obtained from radiation-grafted cation- and anion-exchange membranes.

Two series of ionic polymer-metal composites (IPMCs), one cationic and one anionic, are designed and prepared from radiation-grafted ion-exchange membranes. Through examination of the properties of the membranes synthesized from the two grafting monomers and the two base polymers, acrylic acid-grafted poly(vinylidene fluoride-co-hexafluoropropylene) and quarternized 4-vinylpyridine-grafted poly(ethylene-co-tetrafluoroethylene) with the appropriate amount of ionic groups are employed for the fabrication of cation and anion IPMCs, respectively. The bending displacement of the cation IPMC is comparable to Nafion-based IPMC under direct- and alternating-current voltage, but back-relaxation is not observed. The actuation performance of the anion IPMC is highly improved over those reported earlier in the literature for the other anion IPMCs.

Fabrication and characteristics of a multilayered ionic polymer metal composite based on Nafion/tetraethyl orthosilicate and Nafion/MCNT nanocomposites.

Nafion/multi-walled carbon nanotubes (Nafion/MCNT) and Nafion/tetraethyl orthosilicate (Nafion/TEOS) nanocomposites were prepared and used as starting materials in the fabrication of an ionic polymer metal composite (IPMC). Experimental data show that the Nafion/MCNT-based IPMC exhibited a blocking force that is two times higher than that of bare Nafion-based IPMC. This higher blocking force is due to the stable homogeneous dispersions of multiwalled carbon nanotubes as well as to their improved conductivity. Meanwhile, the Nafion/TEOS-based IPMC generated a blocking force that is more than two times higher than that of bare Nafion-based IPMC because of the induced channels and increased water content. In this paper, a novel Nafion membrane containing a primary Nafion/TEOS layer sandwiched between two outer Nafion/MCNT nanocomposite layers was prepared by consecutive casting of liquid solutions. By using the multilayered Nafion membrane, IPMC was carefully fabricated by electroless plating. In addition, the blocking force, displacement, and electric current of the IPMC were measured on the test apparatus. The multilayered IPMC exhibited a significantly improved blocking force of 6.5 gf as well as a long effective air-operating life time. Finally, this multilayered IPMC was successfully used to actuate the robotic fish.

Investigation of the effects of PWM parameters on ionic polymer metal composite actuators

The effects of the PWM excitation signal parameters, such as frequency and magnitude, on the Nafion-based ionic polymer metal composite (IPMC) actuator response were found out. The first set of experiments was designed to observe the actuator response when the actuators were biased with constant DC voltages. These experimental results were exploited to build an experimental data based dynamic model. The model and these results were also used as references to evaluate the experimental results in the proceeding experiments. The second set of experiments was designed to observe the actuator response when the DC square wave signals at different frequencies (0 to 1000 Hz) were applied. The third set of experiments was designed to observe the actuator response when the PWM signals at different magnitudes (6, 8 and 10 V) were applied. It is observed that back relaxation reduces with increasing frequency, but after a certain frequency value, it remains approximately constant. It is seen that the input output relationship of the actuators are linear only for a range of PWM signal magnitudes. The observations in both the PWM frequency and the magnitude experiments indicated that the performance of the Nafion-based IPMC actuator could be improved by selecting a magnitude of PWM signals between 6–8 Volts and by selecting a frequency between 400–1000 Hz.

Modeling and simulation of the chemo-electro-mechanical behavior of ionic polymer-metal composites

Ionic polymer-metal composites (IPMCs) consist of a thin ionomer plated with metal electrodes. IPMCs exhibit large bending deformations when a small voltage is applied between its electrodes. This bending process is the result of variations in the cation and solvent distribution inside the IPMC. The bending behavior differs for different types of IPMCs, and so a numerical prediction of the behavior needs to be formulated based on various physical phenomena. The bending for several IMPCs can consist of two phases: (1) a fast bending towards the anode and (2) a slow reverse bending. As the physical reasons for reverse bending, i.e., back relaxation of Nafion-based IPMCs is not completely understood, a comprehensive physics-based model of the bending process is still a demanding task. In this paper a numerical model describing the actuation behavior of an IPMC is formulated based on a multi-field approach considering chemical, electrical, and mechanical field equations. This model is based on the cluster model developed by Nemat-Nasser and Li [J. Appl. Phys. 87(7), 3321–3331 (2000)] and Nemat-Nasser [J. Appl. Phys. 92(5), 2899–2915 (2002)] and the chemo-electro-mechanical model given by Wallmersperger et al. [Mech. Mater. 36(5-6), 411–412 (2004); J. Appl. Phys. 101, 024912 (2007)]. The cluster model is a model being able to describe the bending behavior of different IPMCs with and without back relaxation. In the present research the chemical, electrical, and mechanical field equations are discretized using finite differences and solved by a full coupling using the Newton-Raphson technique. By this nonlinear process a detailed representation of the cation and solvent distribution as well as the resulting forces inside the IPMCs are obtained in space and time. Finally a comparison with experimental data published by Nemat-Nasser and Wu [J. Appl. Phys. 93(9), 5255–5267 (2003)] is given for a Nafion-based IPMC with distinctive back relaxation.

High-performance polymer ionomer–ionic liquid membrane IPMC actuator

A high-performance ionic polymer–metal composite (IPMC) actuator based on a polyelectrolyte membrane has been constructed from a poly((t-butyl-styrene)-b-(ethylene-r-propylene)-b-(styrene-r-styrene sulfonate)-b-(ethylene-r-propylene)-b-(t-butyl-styrene)) (tBS-EP-SS-EP-tBS; SSPB) pentablock copolymer ionomer and the ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMImTFSI). The SSPB copolymer ionomer had microphase-separated morphology comprising alternating styrene-rich ionic channel regions and aliphatic EP-rich non-ionic regions, on the several tens of nanometers scale (average diameter of ionic channel regions ca. 20 nm), whereas the most commonly used Nafion contained narrow ion clusters of less than 4 nm. The large ionic channels of SSPB enabled better transport of such bulky ions as IL ions, and endowed the SSPB–BMImTFSI membrane with ionic conductivity superior to that of the Nafion–BMImTFSI membrane (SSPB–BMImTFSI: 1.01 × 10−4 S/cm, Nafion–BMImTFSI: 0.49 × 10−4 S/cm). The SSPB–BMImTFSI membrane-based IPMC actuator generated a larger and faster electromechanical response than the Nafion-based IPMC.

Self-Sensing Control of Nafion-Based Ionic Polymer-Metal Composite (IPMC) Actuator in the Extremely Low Humidity Environment

This paper presents feedforward, feedback and two-degree-of-freedom control applied to an Ionic Polymer-Metal Composite (IPMC) actuator. It presents a high potential for development of miniature robots and biomedical devices and artificial muscles. We have reported in the last few years that dehydration treatment improves the electrical controllability of bending in Selemion CMV-based IPMCs. We tried to replicate this controllability in Nafion-based IPMC. We found that the displacement of a Nafion-based IPMC was proportional to the total charge imposed, just as in the Selemion-CMV case. This property is the basis of self-sensing controllers for Nafion-based IPMC bending behavior: we perform bending curvature experiments on Nafion-based IPMCs, obtaining the actuator's dynamics and transfer function. From these, we implemented self-sensing controllers using feedforward, feedback and two-degree-of-freedom techniques. All three controllers performed very well with the Nafion-based IPMC actuator.