Ionic Polymer Metal Composite Research Articles

A novel strategy to enhance the generating power of ionic polymer metal composites through magnetoelectricity

In this paper, we put forward a method to enhance the output power of ionic polymer metal composite (IPMC) through a magnetic field by combining the ion-electronic and magnetoelectric effects. Firstly, we confirmed that the total output voltage of IPMC deformation originates from the vector superposition of ion-electronic and magnetoelectric effects when applied a magnetic field. The open circuit voltage and output power of IPMC were experimentally investigated by adjusting the deflecting frequency and magnetic field intensity. As the frequency and magnetic field intensity increase, the increased voltage and output power caused by the magnetic field show an upward trend. Then, the experimental results were analyzed and verified through the piezoelectric and magnetoelectric theory. The results show that the increased voltage has a linear relationship with the frequency and magnetic field intensity and has nothing to do with the inherent parameters of IPMC itself. Finally, we performed simulation and practical tests to verify the energy harvesting effect of this strategy. During the energy harvesting test of water flow fluctuation, the open circuit voltage was increased by 41.91% and the output energy was increased by 110.03%, which indicates that this strategy has excellent performance in practical applications. By this study, the power generation performance of IPMC was explored and improved through multiple physical mechanisms.

Ionic Elastomers for Electric Actuators and Sensors

In the past decades, ion conductive polymers and elastomers have drawn worldwide attention for their advanced functions in batteries, electroactive soft robotics, and sensors. Stretchable ionic elastomers with dispersed soft ionic moieties such as ionic liquids have gained remarkable attention as soft sensors, in applications such as the wearable devices that are often called electric skins. A considerable amount of research has been done on ionic-elastomer-based strain, pressure, and shear sensors; however, to the best of our knowledge, this research has not yet been reviewed. In this review, we summarize the materials and performance properties of engineered ionic elastomer actuators and sensors. First, we review three classes of ionic elastomer actuators—namely, ionic polymer metal composites, ionic conducting polymers, and ionic polymer/carbon nanocomposites—and provide perspectives for future actuators, such as adaptive four-dimensional (4D) printed systems and ionic liquid crystal elastomers (iLCEs). Next, we review the state of the art of ionic elastomeric strain and pressure sensors. We also discuss future wearable strain sensors for biomechanical applications and sports performance tracking. Finally, we present the preliminary results of iLCE sensors based on flexoelectric signals and their amplification by integrating them with organic electrochemical transistors.

Improving the torsion performance of IPMC by changing the electrode separation

Ionic polymer metal composites (IPMCs) are widely studied as actuators and sensors, due to their large bending motion, flexibility and being light-weight. Nowadays, IPMCs are used in the bionic field, for example, to achieve bending and twisting movements of wings and fins. In this paper, a method is proposed to optimize the torsion performance of IPMCs by changing the electrode separation. The IPMCs with patterned electrode fabricated by masking technique are proposed to accomplish twisting motion. The result indicates that the torsion performance is improved as the electrode separation increased. Thereby it provides a new strategy for the bionic field with twisting behavior.

Taste Sensor Using Ionic Polymer Metal Composite

The usage of ionic polymer metal composite (IPMC) being an electroactive polymer is prevalent in different engineering applications. IPMC are synthetic composite nanomaterials which show artificial muscle behavior under applied voltage or electric impetus. When an electrical potential is applied across the two membranes, the positively charged conjugated and hydrated cations migrate toward the negative electrode. This migration creates an osmotic pressure gradient across the membrane; hence, the strip gets deformed or bent. On the other hand, IPMC strips are capable of generating electrical potential under the action of stretching or bending (thereby acting as a sensor). In this letter, the authors report the pragmatic application of the IPMC strip to study a taste sensor. The sensing characteristics of IPMC strips are applied to sense five general tastes (sweet, sour, bitter, salty, and spicy). Primarily, IPMCs are immersed into individual solutions and kept for 15 min for doping action. Thus, different solutions having distinct concentration of ions will lead to distinct identifications. In this present investigation, the authors have instigated the IPMC strip as a sensor; when an IPMC strip is bent or deformed, an analogous voltage in the range of millivolts is generated across the membranes. Second, clammy IPMCs are bent in the clockwise and again in the counterclockwise direction (10°) to record the corresponding voltage. A set of experimental data was collected, which divulged unique characteristics for different solutions pertinent to different tastes. Thus, IPMC strips are able to recognize different taste senses.

Cooperative Collision Avoidance Control of Servo/IPMC Driven Robotic Fish With Back-Relaxation Effect

In this letter, a collision avoidance control strategy is developed for a robotic fish that is propelled by a two-joint fishtail, comprising a servo motor and an ionic polymer-metal composite (IPMC), which are used as solid and soft actuators, respectively. In this dual-actuator system, the forward motion of the fish is controlled by the servo motor, which generates a flapping motion at its first joint, and the turning motion of the fish is controlled by bending the IPMC at its second joint. When a constant voltage is applied to the IPMC, the robotic fish is observed to demonstrate a short-term turning characteristic, and this is attributed to the back-relaxation phenomenon inherent in the IPMC. In order to capture this unique characteristic, a data-driven approach is adopted to model the fish's lateral acceleration response when subjected to an IPMC voltage input. Experimental tests, including bending tests on an individual IPMC slice and turning tests on the robotic fish (with the servo/IPMC tail), are conducted to collect sufficient data to identify a transfer function that relates the voltage applied to the IPMC with the lateral acceleration response of the fish. This transfer function is then integrated with a collision avoidance control law (based on the collision cone concept) to determine the IPMC voltages for a pair of robotic fish to avoid collisions. Experiments are performed to validate the collision avoidance control law.

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.

A 3D analytical ion transport model for ionic polymer metal composite actuators in large bending deformations

Ionic polymer metal composites (IPMCs) are a kind of soft electroactive polymer composites. An IPMC strip commonly has a thin polymer membrane coated with a noble metal as electrodes on both sides. Whenever an electric voltage is applied to the IPMC, it bends and whenever it is deformed, a low voltage is measurable between its electrodes, hence IPMC is an actuator as well as a sensor. They are well known for their promising features like low density, lightness, high toughness and remarkable stimulus strain, also, they have the potential for low-voltage operation while exhibiting acceptable large bending deformation. In this paper, a three-dimensional (3D), dynamic and physics-based model is presented analytically and experimentally for IPMC actuators. The model combines the ion transport dynamics within the IPMC and the bending dynamics of it as a beam under an electrical stimulation. In particular, we present an analytical model to create a relation between the input voltage and the output tip displacement of an IPMC actuator for large bending deformations. Experimental results show that the proposed model captures well the tip displacement.

Liquid Metal Logic for Soft Robotics

While there are many soft matter sensing and actuation technologies, there is far less choice when it comes to soft material devices for control and computation. One solution is the Soft Matter Computer (SMC) which can perform both analogue and digital computations in soft materials. This computer processes a fluidic input pattern consisting of alternating regions of conducting and insulating fluids into an electronic output signal. However, the use of salt water as the conductive fluid means that the Soft Matter Computer has high electrical resistance and requires an AC voltage, making untethered operation impractical. In this letter, we introduce the liquid metal Soft Matter Computer (LM-SMC), which uses galinstan as an alternative conductive fluid. We show that by switching to a liquid metal-sodium hydroxide fluidic input, we reduce the electrical resistance of the SMC by three orders of magnitude, allowing operation at DC voltages of 2 Volts and under. We characterise the stability of the liquid metal input patterns and demonstrate the potential of the LM-SMC by using it to control bipolar ionic polymer metal composite and shape memory alloy actuators. By enabling fully soft computation and control of multiple actuators from a single low voltage DC source, the LM-SMC enables a new class of intelligent and untethered soft machines.

Investigation of Ionic EAP Actuators with Metal and Polymer Electrodes in Aqueous Medium

Electroactive polymers (EAP) are promising materials for creating electromechanical transducers. Among ionic EAP, ionic polymer-metal composites (IPMC), which are an ion-exchange membrane with metal electrodes on both sides, have been widely spread and well studied. The evolutionary development of IPMC results in ionic polymer-polymer composites (IP2C), in which polymer electrodes are used. To obtain IPMC actuators with platinum electrodes, the method of chemical reduction from the salt solution was chosen, and to obtain IP2C actuators with PEDOT electrodes, the method of in situ polymerization of the monomer on the membrane surface was chosen. Samples of 2x0.5 cm in size based on the MF-4SK membrane with a thickness of 290 μm were preliminarily kept in deionized water (H+ form) and in 0.1 M CuSO4 aqueous solution (Cu2+ form), after which their performance was studied in air, in deionized water, as well as in aqueous solutions of CuSO4 and NaCl. When applying a DC voltage and a sine wave AC voltage, a decrease in the maximum displacement and peak-to-peak displacement of the IPMC actuators and IP2C actuators with an increase in the ionic strength of the liquid was observed, except for the case of the IPMC actuator operation in CuSO4 aqueous solutions. In all considered media, the IPMC actuators and IP2C actuators in Cu2+ form displaced more strongly than the corresponding samples in H+ form, except for the IP2C actuators in deionized water. The largest peak-to-peak displacement was demonstrated by the IPMC actuators in Cu2+form when operating in air (5 mm) and the IP2С actuators in H+ form when operating in deionized water (8.4 mm).

Control of an IPMC Soft Actuator Using Adaptive Full-Order Recursive Terminal Sliding Mode

The ionic polymer metal composite (IPMC) actuator is a kind of soft actuator that can work for underwater applications. However, IPMC actuator control suffers from high nonlinearity due to the existence of inherent creep and hysteresis phenomena. Furthermore, for underwater applications, they are highly exposed to parametric uncertainties and external disturbances due to the inherent characteristics and working environment. Those factors significantly affect the positioning accuracy and reliability of IPMC actuators. Hence, feedback control techniques are vital in the control of IPMC actuators for suppressing the system uncertainty and external disturbance. In this paper, for the first time an adaptive full-order recursive terminal sliding-mode (AFORTSM) controller is proposed for the IPMC actuator to enhance the positioning accuracy and robustness against parametric uncertainties and external disturbances. The proposed controller incorporates an adaptive algorithm with terminal sliding mode method to release the need for any prerequisite bound of the disturbance. In addition, stability analysis proves that it can guarantee the tracking error to converge to zero in finite time in the presence of uncertainty and disturbance. Experiments are carried out on the IPMC actuator to verify the practical effectiveness of the AFORTSM controller in comparison with a conventional nonsingular terminal sliding mode (NTSM) controller in terms of smaller tracking error and faster disturbance rejection.

Fast-moving piezoelectric micro-robotic fish with double caudal fins

Micro-robotic fish (length ≤10 cm) driven by smart materials have remarkable advantages over conventional motors and piston-based robotic fish. In particular, they are highly efficient and compact. One of the key challenges is attaining high mobility with high energy density, low driving voltage and power loss. In this work, a double caudal fin micro-robotic fish actuated by two piezoelectric bimorph cantilevers is proposed and fabricated from rigid carbon fiber/resin composites and flexible polyimide hinges. Its weight is about 1.93 g and the maximum uniform swimming velocity is as high as about 0.75 BL/s (4.5 cm/s), which is much faster than previously reported micro-robotic fish actuated by ionic polymer–metal composites, shape memory alloys and dielectric elastomers. A theoretical model is validated by the experimental results and can be used to design and analyze a variety of piezoelectric robotic fish propelled by caudal fins.

Ionic polymer–metal composite actuators driven by methylammonium formate for high-voltage and long-term operation

Ionic liquids (ILs) have been exploited as the internal solvent in the development of ionic polymer–metal composite (IPMC) actuators capable of long-term operation. However, a major issue is that most IPMCs impregnated with conventional ILs are yet to be practically applied due to insufficient actuation performance. Herein, methylammonium formate (MAF), an IL with low viscosity, small ionic size, high ionic conductivity, and excellent electrochemical stability, is introduced as a new internal solvent for IPMCs to achieve both excellent operation characteristics and long-term stability. The actuation characteristics of a series of IPMCs impregnated with four types of ILs, including MAF, were analyzed. The MAF-based IPMCs had more than twice the displacement and three-fold higher blocking forces compared with other IL-based IPMCs. Moreover, unlike conventional water-driven IPMCs, the MAF-driven IPMCs operated even at high voltages (4V) without solvent loss and electrolysis. Their initial displacement remained above 81% even after operating for 2160 cycles (6h). This simple change of media in IPMC actuators is expected to advance the design of IPMCs with improved displacement, force generation, and stability.

Energy-Based Modeling of Ionic Polymer–Metal Composite Actuators Dedicated to the Control of Flexible Structures

This article deals with the control-oriented energy-based modeling of ionic polymer–metal composite (IPMC) patches using multiscale infinite dimensional port-Hamiltonian formulations and Lagrange multipliers. Inspired by the work of Nishida <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> in 2012, but considering different assumptions, this article focuses on the constraints arising from the coupling between the polymer gel and the compliant mechanical structure of the actuator, under the quasi-static mechanical assumption for the gel, leading to a constrained port-Hamiltonian system. The geometric structure of the overall system and the associated energy balance are derived. The proposed energy-based model of the IPMC actuator allows deriving controllers via energy-based control design methods with a clear physical interpretation. The proposed actuator model is further discretized in space using a structure preserving finite difference method. The Lagrange multipliers are eliminated using coordinate projections. Simulations are compared with experimental results. With proper discretization numbers, our model is consistent with the physical system. Finally, Lagrange multipliers are exploited to connect the actuator to a 2-D flexible structure stemming from the modeling of a flexible endoscope.

Electroless copper deposition and interface characteristics of ionic electroactive polymer

In this study, the cheap copper electrode ionic polymer metal composite (IPMC) was prepared by chemical deposition. The formation mechanism of the copper electrode layer was analyzed firstly, then the surface and cross section morphology, roughness and porosity of IPMC were measured, and the interface profile was simulated and predicted based on Weierstrass-Mandelbrot (WM) function, at last, the adhesion force of the interface was calculated. The results show that the coarsening of Nafion and the adsorption of Ag+ ions provide a good catalytic activation site for the nucleation and rapid growth of copper particles. The copper layer on the surface of IPMC is arranged in granular, distributed compactly and uniformly, with the porosity of 52.3% and a strong (111) preferred orientation, which are beneficial to the performance of IPMC. Based on the WM function, the fractal dimension, characteristic scale and characteristic roughness are used to reflect the flatness and complexity of surface profile. The adhesive strength between the substrate and the coating is mainly due to the surface force field caused by the coarsening treatment. The theoretical and simulation studies of the interface characteristics are helpful to understand the internal mass transfer mechanism of IPMC and characterize the complex interface morphology, which also lays a foundation for the later research and application of IPMC.

NAFAS: Non-Rigid Air Flow Active Sensor, a Cost-Effective, Wearable, and Ubiquitous Respiratory Bio-Sensor

A Non-rigid Air Flow Active Sensor (NAFAS) to detect the respiratory patterns is introduced in this paper. The main part of NAFAS is an ionic electroactive polymer-based i-EAP soft sensor. It can accurately detect breathing patterns and has promising features to develop low cost, wearable, and ubiquitous spirometers. Patients with respiratory diseases need to take pulmonary function tests consistently. Hence, it is time-consuming and expensive. To address these problems, NAFAS presents point-of-care testing (POCT) of the respiratory system's function. The proposed i-EAP based sensor is a small strip of Ionic Polymer Metal Composite (IPMC) that has been fabricated using a Nafion membrane and two Pt electrodes. A test, including different breathing patterns, is designed and is performed by several male and female subjects. Results show that the NAFAS can detect delicate breathing patterns with various frequencies in an appropriate manner.

Modeling actuation and sensing in ionic polymer metal composites by electrochemo-poromechanics

Ionic polymer metal composites (IPMCs) consist of an electroactive polymeric membrane plated with metal electrodes. They hold promise as actuators and sensors for soft robotics and biomedical applications. Their capabilities ensue from the motion, within the membrane, of a fluid phase consisting of ions dispersed in a solvent. Toward a thorough understanding of IPMC multiphysics, we propose a large deformation theory combining electrochemistry and poromechanics. Namely, we modify the theory recently developed by Porfiri’s group by introducing the transport of the solvent, whose redistribution determines the volumetric deformation of the fluid-saturated membrane, and we further account for the cross-diffusion of solvent and ions. In actuation, the imposed voltage drop across the electrodes triggers ion migration, such that the solvent is transported toward the cathode by electro-osmosis. This determines the initial bending toward the anode; then, back-relaxation occurs because of both the solvent counter-diffusion and the asymmetric redistribution of ions near the electrodes. In short-circuit sensing, the applied load triggers solvent motion, such that ions are mainly transported toward the cathode by convection with the solvent. This determines charge accumulation; then, ion counter-diffusion leads to a decrease of the charge stored at the electrodes. We demonstrate that these behaviors can be predicted by the proposed theory on the basis of relevant finite element benchmarks. Additionally, our analysis encompasses the assessment of the role of the membrane elastic moduli in the counter-diffusion of solvent and ions in IPMC actuation and sensing.

Graphene Oxide-Polyaniline Coating on Ionic Polymer Blend Membrane for Actuation

Ionic polymer metal composites (IPMC) can be used as actuators and sensors and intrinsically have low activation voltage and large bending strain, which help to transform electrical energy to mechanical energy and can be utilized as bidirectional material. In this study, the ionic polymeric blend films/membranes of PVDF:PSSS:PVP in the blend ratio of 40:30:30; 50:30:20 and 60:15:25 (wt.%) is presented. The membranes were prepared by solution cast technique and coated with graphene oxide (GO)-polyaniline (PANI). Membranes were characterized by X-ray diffraction, optical microscopy. Electrical conductivities at different frequencies and water uptake properties were also determined. The actuating performance of PVDF:PSSS:PVP and water uptake of blend membrane was found to be maximum for the blend ratio of 60:15:25. PVDF:PSSS:PVP with blend ratio (60:15:25) also exhibited highest actuation at 10 V DC. Graphene oxide was prepared and characterized by using FTIR and Raman spectra. A brief account of the fabrication of IPMC and its actuation application was also presented.

A review of coating materials for ionic polymer metal compounds for Nafion-117

The actuators based on ionic polymer metal composites or smart material are popular among many fields as robotic applications, biomedical applications and biometric applications due to their low actuation energy and high bending property on the application of voltage less than 4 V voltage. The Nafion-117 is being used as base material coated with the noble material for the same purpose. The coating is implemented to increase the thermal stability and water resistance property. The high cost of noble material coating increased the cost of IPMC 50% making its use limited in the industrial applications. The noble material used for this purpose is platinum, gold and silver. This paper emphases on reducing the cost of coating materials for Nafion-117 based IPMC. The various materials such as palladium, manganese oxide, titanium, lithium group materials and para-xylene group were compared for the purpose. The focused is done on reducing the coating cost by not compromising the efficiency to some extent. The sandwiched layer of IPMC that is nafion or flemion between the layers of noble material are most popular among fuel cells, artificial muscles and other robotic applications.The present comparative study has been done to develop a cheap smart material for industrial purpose and in biological applications like artificial muscles and coating of various elements.

Modelling the effect of crack formation on the actuation behaviour of ionic polymer metal composite

In this paper, the effect of different cracks on the platinum electrode region of an IPMC actuator which occurs due to its continuous bending is modelled. The IPMC actuator is modelled in a cantilever configuration using COMSOL Multiphysics 5.3 a finite element method solver. The thickness of Nafion (polymer) membrane and (platinum) electrode 267 μm and 20 μm (each side) and the full length of IPMC is 36 mm long and width is 6 mm. Experimental results showing the deflection and frequency of IPMC with the same dimensions are noted and the simulation results for the same beam dimensions are validated with the experimental results. Studies are carried out on (a) different shapes of cracks (V, U, and rectangular shape) on electrode region, (b) depth and position of the cracks on the electrode, (c) the effect of presence multiple cracks on the top and bottom electrode. The change in the IPMC's resonance frequency and tip deflection for various cracks is studied and compared with the IPMC with no cracks. IPMC with U-shaped cracks has the highest deflection of 2.88 mm when cracks are located on single side and rectangular cracks have the highest deflection of 3.06 mm when cracks are located on both sides of IPMC as compared to 2.5 mm without any cracks on the electrode. These studies reveal that the U shaped single crack and rectangular double sided cracks largely affect the IPMC actuation behaviour thus altering its deflection values. The effect of location of cracks suggests that cracks near the free end of IPMC affect the deflection more compared to that near fixed end.

A fractional order model for electrochemical impedance of IPMC actuators based on constant phase element

The accurate modeling of electrical impedance over a wide range of frequency is essential for precise dynamic modeling and control problems of Electroactive Polymer (EAP) actuators. Recently, fractional order modeling has attracted more attention due to the high accuracy. This paper deals with a fractional order electrical impedance model and its identification procedure for a class of EAP actuator named Ionic Polymer Metal Composite (IPMC). To take IPMC’s fractional characteristic into account, constant phase element (CPE) is used to construct a model structure according to Electrochemical Impedance Spectroscopy (EIS). By employing the Levy’s method in combination with genetic optimization algorithm, the unknown parameters of the resulting fractional transfer function are identified. Finally the proposed model is verified, by comparing with experimental EIS data. The results show that the fractional order model has high accuracy for representing the electrical impedance of IPMC actuator. The proposed modeling procedure is general and can also be used for any type of EAPs.