Ionic Polymer Metal Composite Actuators Research Articles

Development of IPMC actuators with high bending uniformity and orientation

Abstract Ionic polymer-metal composite (IPMC) actuators have attracted considerable scientific interest in the field of robotics and artificial muscles due to their low operating voltage, high strain capacity, and lightweight. However, the non-uniform bending of IPMC actuators affects their control accuracy and limits their potential applications. In this work, the surface voltage of IPMC actuators was measured and the internal electric field distribution was numerically computed. It was concluded that the non-uniform bending is mainly due to the non-uniform distribution of hydrated cations inside the IPMC as a result of the inhomogeneous electric field. The bending uniformity is improved by sputtering a gold layer on the surface of the IPMC actuator, and a support strip is introduced to limit the bending of the IPMC in the width direction, resulting in an improvement of its pointing characteristics. It is found that the bending uniformity of IPMC improved by 108.32% and 220.63% by sputtering at an input voltage of 2.5V and 5V respectively. When the input voltage is fixed at 2.5V and 5V, the bending in the width direction is reduced by 92.31% and 95.17% with the support structure, respectively.

Possible design/fabrication of a soft biomimetic magic (flying) carpet made with Ionic Polymer Metal Composites (IPMCs)

A novel design of an artificial soft robot similar to the motions of a magic carpet is presented. Reported in the planning, designing, and fabricating of a biomimetic magic (flying) carpet made with ionic polymer metal composites (IPMCs). A new family of IPMC sensors and actuators is proposed to be used as a flexible plate and a flexible carpet to form a biomimetic flexible soft sensor and actuator system. The magic carpets made with IPMCs will be experimentally capable of bending, rolling, turning, twisting, and simultaneous sensing. However, their sensing characteristics as a soft biomimetic magic carpet feedback sensor are shown to have great potential for ubiquitous robot-human interactions (RHI). Upon various types of deformation, they are shown to generate unique output voltage signals and transient currents to be correlated to the actual magic carpet feedback force. Furthermore, a flexible sheet of IPMC can be actuated simultaneously on the fly by a small power supply embedded in the magic carpet. The magic carpet version of IPMC can be applied as smart skin to develop human-like dexterous and soft manipulation.

Electrically Reconfigurable Metasurfaces for Frequency Selective Transmission via IPMC Kirigami

AbstractMetasurface with programmable configurations has attracted tremendous attention due to their exotic abilities to manipulate electromagnetic waves. Herein, an electrically reconfigurable metasurface for frequency selective transmission is developed based on ionic polymer–metal composite (IPMC) kirigami. First, low‐voltage driven IPMC actuators with stable actuation performance are realized, and then a thermomechanical equivalent model and a numerical electromagnetic analysis model are proposed for evaluating the deformation of the IPMC actuators and predicting the electromagnetic tunable properties of the IPMC kirigami metasurfaces, respectively. Subsequently, large‐area IPMC kirigami metasurfaces are proposed and produced by using programmable nanosecond laser micro‐processing technique that endows the uniformity of the kirigami units. Finally, the electromagnetic functionalities of these IPMC kirigami metasurfaces are researched and validated by experiments and numerical simulations. Both theoretical and experimental results demonstrate that the electromagnetic transmission frequency of the fabricated IPMC kirigami metasurface with 10 × 10 units can be tuned from 19.3 to 20.8 GHz by the application of a low voltage of 3 V. Compared with the existing reconfigurable metasurfaces, the proposed IPMC kirigami metasurface demonstrates clear advantages in its compact structure, lower driving‐voltage, low‐acoustic noise, and wide working frequency range.

Application‐Oriented Modeling of Soft Actuator Ionic Polymer–Metal Composites: A Review

Compared to conventional actuators, the soft ionic polymer–metal composite (IPMC) actuator has significant advantages in specific applications, and the mathematical model of IPMC actuators is essential to comprehending and applying IPMCs. Due to the inherent characteristics of IPMCs and the impact of the manufacturing and measurement processes, it is challenging to developa reliable model. This article provides a comprehensive overview of the developments in IPMC actuator modeling. In particular, three types of models are examined and contrasted: the nonphysical identification model, the partial‐physical model, and the physical‐based model. In order to comprehend the current state of numerous IPMC actuator models, the characteristics, evolution, and functions of each type of model are discussed. Afterward, the evolution of the IPMC actuators’ applications is discussed. Finally, promising research directions for IPMC actuator models are identified that can more effectively facilitate the development of IPMC‐based devices.

Gold nanowire mesh electrode for electromechanical device

Ionic polymer-metal composite (IPMC) actuators were prepared with Nafion film as the ionic polymer and gold nanowire (Au-NW) mesh film as the metal electrodes by hot-pressing, which shortened preparation time within 1 h. As a reference, IPMC actuator consisting of Nafion film and gold foil (Au-foil) was also prepared. Au-NW mesh film can be an electrode with thinner (about 150 nm) and lower surface resistivity (about 0.5 Ω sq−1) than the conventional electrode prepared by electroless plating. Larger contact area of the Au-NW mesh electrode than the Au-foil electrode resulted in better actuation performance (60% larger peak-to-peak displacement in actuation). It was confirmed that the transformation behavior of Au-NWs differed depending on the external stimuli condition. Namely Au-NWs transformed to Au nanoparticles in the case of the heat stimulus only. Meanwhile, Au-NWs transformed to plates in the case of the heat and pressure stimuli. While higher temperature improved the adhesion of Au-NW mesh electrode to the Nafion surface, it induced the transformation of nanowire to plates. The IPMC actuator that the Au-NW mesh electrodes were hot-pressed at 90 ºC exhibited the highest capacitance and the largest peak-to-peak displacement in actuation. This research expanded the application field of gold nanowires to the electromechanical devices.

Development of ionic polymer metal composite actuator by EB graft-polymerization

Ionic polymer-metal composites (IPMC) actuators were fabricated by applying ionic exchange groups such as sulfonic acids and carboxylic acids using EB graft-polymerization to two types of fluorine-based copolymers (Poly (tetrafluoroethylene-co-hexafluoropropylene): FEP and Poly (ethylene-co-tetrafluoroethylene): ETFE) as base materials, and then forming electrodes with Pt-Pd by sputtering. The physical properties of the obtained graft membrane and the evaluation as an actuator were performed. It was suggested that the acrylic acid graft membrane is preferable for PEM as components of IPMC actuator, because the ion conduction mechanism is a vehicle mechanism in which oxonium ions pass through formed hydrated clusters in PEM. In the case of operation at 10 V, IPMC actuator based on the acrylic acid-grafted FEP and ETFE showed similar or larger displacement than that based on conventional membrane. The grafted ETFE, which has high mechanical properties, is superior to the grafted FEP used in the actuators. Therefore, it was found that the ETFE grafted with acrylic acid is preferable for the IPMC actuator.

Effects of Varied Planar Dimensions of IPMC on Simulated Actuation using COMSOL

This study focuses on mechatronic systems and their use of bending smart materials, specifically the ionic polymer metal composite (IPMC), for compliant actuation. The advantages of IPMC actuators, such as low power consumption and high flexibility, are highlighted. The actuation mechanism of IPMCs involving ion migration, water transport, and mechanical stress imbalance is discussed. The influence of geometric parameters, specifically length and width, on IPMC performance is investigated through simulations. Results show a positive correlation between IPMC lengths exceeding 30 mm and displacement, with longer lengths leading to higher displacements. The relationship between width and maximum displacement is attributed to factors like increased active area, larger polymer volume, and potential effects on mechanical properties. Further electromechanical analysis is needed for a comprehensive understanding of these mechanisms.

High water content electrically driven artificial muscles with large and stable deformation for soft robots

Ionic-polymer metal composites (IPMCs) actuators show great potential for soft robots due to their large deformations and fast responses at low voltage. However, realizing large and stable deformation remains a challenge since the existence of back relaxation phenomena. Herein, we report high-performance IPMCs actuators fabricated via solution-casting and isopropanol-assisted electroless plating methods. The actuator exhibits extremely large bending deformation (125°) and ultrafast initial response speed (1.09 % s−1 bending strain rate) within one second of the start time under the DC voltage of 3 V. Furthermore, the actuator exhibits no significant back relaxation, even when it lifts objects 11 times heavier and holds up for more than 695 s. The outstanding properties of the actuator are demonstrated by various soft robots, including a guide-grapple robot and a microarchitecture for robotic metamaterials, and a finite element simulation approach is proposed to model the robotic metamaterials. This study offers a viable means for developing high-performance artificial muscles without back relaxation for promising applications in biomedical devices, robotic metamaterials, and soft robotics.

Nafion-Pt IPMC electroactive behavior changes in response to environmental nonequilibrium conditions

Electroactive polymers (EAPs) continue to gain attention for their potential to offer unique and versatile solutions in the soft robotic and flexible electronic industries. Ionic polymer-metal composites (IPMCs) are a class of ionic-type EAPs which can be configured as capacitor actuators with very low voltage requirements (⩽5 V AC or DC). Their compact, portable, and lightweight properties, coupled with a biomimetic bending actuation response make them ideal for human-machine integrated technologies such as medical implants, active skins, and artificial muscles. This work tested the IPMC’s actuation and electrical response in varying saturation conditions (70% RH, 85% RH, 95% RH, and DI water liquid immersion) and voltage application schemes (direct current voltage (DCV) cycled, continuously applied, and relaxation responses upon voltage removal). This information was then used to establish actuation and back-relaxation response patterns through repetitive testing for statistical certainty. These demonstrated maximized actuation in water vapor conditions where the IPMC’s dielectric permittivity is maximized (), and the dissipation factor is minimized (). The response trends in vapor conditions are gradual but yield larger actuation ranges with increasing hydration. Liquid immersion restricts the IPMC’s range of motion but produces a sharper response pattern. These trends were validated against previously published IPMC actuator models. All of this creates a more pragmatic perspective on the potential of this technology which aids in the advancement of this material’s evolution towards viable real-world application configurations which capitalize on the material’s natural responses.

Three-layer ionic polymer–metal composite actuator with functionalized carbon nanotubes incorporated into Nafion

Three-layer ionic polymer–metal composite actuator with functionalized carbon nanotubes incorporated into Nafion

Analysis of a Soft Bio-Inspired Active Actuation Model for the Design of Artificial Vocal Folds

AbstractPhonation results from the passively induced oscillation of the vocal folds in the larynx, creating sound waves that are then articulated by the mouth and nose. Patients undergoing laryngectomy have their vocal folds removed and thus must rely on alternative sources of achieving the desired vibration of artificial vocal folds. Existing solutions, such as voice prostheses and the Electrolarynx, are limited by producing sufficient voice quality, for instance. In this paper, we present a mathematical analysis of a physical model of an active vocal fold prosthesis. The inverse dynamical equation of the system will help to understand whether specific types of soft actuators can produce the required force to generate natural phonations. Hence, this is referred to as the active actuation model. We present the analysis to replicate the vowels /a/, /e/, /i/, and /u/ and voice qualities of vocal fry, modal, falsetto, breathy, pressed, and whispery. These characteristics would be required as a first step to design an artificial vocal folds system. Inverse dynamics is used to identify the required forces to change the glottis area and frequencies to achieve sufficient oscillation of artificial vocal folds. Two types of ionic polymer-metal composite (IPMC) actuators are used to assess their ability to produce these forces and the corresponding activation voltages required. The results of our proposed analysis will enable research into the effects of natural phonation and, further, provide the foundational work for the creation of advanced larynx prostheses.

Improved ionic and mechanical properties of ion-exchange membrane with an ionic silica network for high-performance ionic polymer-metal composites

Ion-exchange membranes considerably affect the actuation of ionic polymer–metal composites (IPMCs) through ion movement under an applied voltage. To enhance the performances of IPMCs, previous studies have increased the ionic content of the ion-exchange membrane, thereby improving its ionic conductivity and water uptake. Although this increased ionic content enhances IPMC displacement, the increased water uptake diminishes IPMC stiffness, resulting in decreased IPMC blocking force. Therefore, a new approach is needed to resolve the trade-off between displacement and force. Here, we reinforced the Nafion membrane by forming a sulfonated polysilsesquioxane structure inside. The incorporation of this ionic silica network increased the total ion content of the membrane and included silica as a mechanically reinforcing filler. The force of the IPMC can be enhanced despite increased water uptake by the membrane. Therefore, IPMCs were obtained with improvements in displacement and blocking force. Comparison of the IPMCs with commercial Nafion films revealed similar displacement and superior force, demonstrating their applicability. These findings represent a breakthrough in enhancing the actuation of IPMCs while resolving the trade-off between displacement and force.

Enhanced Ionic Polymer-Metal Composites with Nanocomposite Electrodes for Restoring Eyelid Movement of Patients with Ptosis.

The present study aims to use enhanced ionic polymer-metal composites (IPMC) as an artificial muscle (a soft-active actuator) to restore eyelid movement of patients with ptosis. The previous eyelid movement mechanisms contained drawbacks, specifically in the lower eyelid. We used finite element analysis (FEA) to find the optimal mechanism among two different models (A and B). In addition to common electrodes of IPMC (gold and platinum), the bovine serum albumin (BSA) and microcrystalline cellulose (MCC) polymers, with optimal weight percentages of carbon nanotube (CNT) nanofiller, were also utilized as non-metallic electrodes to improve the efficiency of the IPMC actuator. In both models, IPMC with nanocomposite electrodes had higher efficiency as compared to the metallic electrodes. In model A, which moved eyelids indirectly, IPMC with MCC-CNT electrode generated a higher force (25.4%) and less stress (5.9 times) as compared to IPMC with BSA-CNT electrode. However, the use of model A (even with IPMCs) with nanocomposite electrodes can have limitations such as possible malposition issues in the eyelids (especially lower). IPMC with MCC-CNT nanocomposite electrode under model B, which moved eyelids directly, was the most efficient option to restore eyelid movement. It led to higher displacements and lower mechanical stress damage as compared to the BSA-CNT. This finding may provide surgeons with valuable data to open a window in the treatment of patients with ptosis.

Influence of environmental conditions and voltage application on the electromechanical performance of Nafion-Pt IPMC actuators

Ionic polymer–metal composites (IPMCs) are a class of ionic-type electroactive polymers which can be configured as capacitor actuators with very low voltage requirements (⩽5 V AC or DC). Their compact, portable, and lightweight properties, coupled with a biomimetic bending actuation response, makes them ideal for human–machine integrated technologies such as medical implants, active skins, and artificial muscles. Unfortunately, IPMC actuator’s hydration-related sensitivity inhibits practical application in industry and makes experimental research difficult. Therefore, this research sought to quantify the hydration-related parameters of IPMC actuators by applying a wide range of experimental tests to characterize the material’s hydration-dependent features. This included saturation, dielectric, and bending actuation measurements. The IPMC’s degree of saturation properties were classified to establish sample rehydration, preparation, and preservation techniques. IPMC electrical-solvent properties were measured to estimate IPMC actuation performance based on capacitance and dissipation measurements. Maximized actuation was identified for samples tested in 95% RH (i.e. percentage relative humidity). This condition produced an optimized displacement range and retained quality. Through statistical analysis, the work showed large electroactive performance variability (up to 50% deviation), which is a primary obstacle inhibiting this technology from practical application. Finally, an array of electrical field bias applications (i.e. cycled, constant, and post voltage removal monitoring) at intensities ranging from 0.75 to 1.2 V (direct current voltage) were used to quantify actuation rate, maximum displacement, as well as voltage application and removal back-relaxation behavior.

Additive manufacture of ionic polymer–metal composite actuators using digital light processing techniques

PurposeThe purpose of this study is to develop a additive manufacturing (AM) process for the fabrication of ionic polymer–metal composite (IPMC) devices with complex designs that would be time-consuming to replicate using conventional manual methods. These IPMC devices have considerable potential in electroactive polymers (EAPs) and soft actuators.Design/methodology/approachThis paper presents a novel three–dimensional (3D) AM technique to develop IPMCs. Digital light processing (DLP) fabrication of soft EAPs was undertaken using a vat-based AM method, followed by deposition of cost-effective outer silver electrodes.FindingsDLP-fabricated devices were compared to conventional Nafion™-117 devices. DLP layer-by-layer fabrication of these devices allowed for good resolution for a range of printed objects. Electrical actuation of the DLP-produced IPMCs showed tip displacements of up to 3 mm, and greater actuation was seen in the presence of lithium rather than magnesium cations. The IMPCs showed good ion exchange capacities, while electrochemical analysis showed the reversible formation and removal of AgCl layers in addition to ion movement.Practical implicationsThe AM of these devices allows for rapid prototyping as well as potential use in the development of multiple degrees of freedom actuators and devices.Originality/valueAn original resin formulation was developed for DLP 3D printing. This formula is chemically distinct from the conventional Nafion™-117 membranes that can be purchased. Additionally, this method allows for the manufacture of complex objects that would be difficult to machine by hand. These findings are of value to both the fields of polymer chemistry and AM.

Integrated fabrication process with multiple optimized factors for high power density of IPMC actuator

ABSTRACT Ionic polymer-metal composites (IPMCs) are typical smart materials that are commonly used in bionic applications, including soft robots, bionic flapping aircraft, and bionic fish. However, their low output force seriously limits device performance. Stacking of multiple IPMC actuators to improve the overall performance of soft actuators is a strategy that is used in practical applications. Under the energy dissipation condition in the IPMC stacking structure, if each single IPMC in the structure has high power density, the structure will produce excellent performance with high efficiency that can greatly promote wider application of IPMC actuators. To meet this requirement, a method for fabrication process integration with multiple optimized factors was used to obtain IPMC materials in this paper. Carbon nanotube (CNT) doping, isopropyl alcohol-assisted plating, and hot pressing with a mesoscopic structural mold were selected as typical optimization methods for process integration and were initially investigated separately to determine the optimal process parameters. By combining the best process parameters in an integrated process, the IPMC treated by isopropyl alcohol-assisted plating and CNT doping process (No. AC7) showed excellent actuation performance and high work density (~9.71/12.36 gf, ~14.93/31.89 kJ/m3 under 3/4 VDC). The enhanced performance meets the requirements for practical bionic applications.

Dynamic modeling of a fish tail actuated by IPMC actuator based on the absolute nodal coordinate formulation

Ionic polymer metal composite (IPMC) is a smart material with low driving voltage, high energy conversion, light weight and simple structure. It is suitable for driving the tail fin of small bionic fish. Actuators made of this material are quite flexible, and they are laborious to accurately describe the complex deformation of structures. Absolute nodal coordinate formulation (ANCF) has great merits in describing large deformation and large displacement problems. In this paper, the feasibility of ANCF in dynamic modeling of a fish tail actuated by IPMC actuator will be explored for the first time. The tail fin is simplified into two forms: a pure flexible IPMC beam and a hybrid beam that consists of an IPMC beam and a fixed rigid beam. The ANCF one-dimensional two-node beam element is adopted. Considering the influence of deformation curvature, the exact expression of generalized elastic force is obtained. The proposed dynamic model can describe the large deformation problem of the flexible beam. The dynamic responses of the pure IPMC beam tail fin and the hybrid tail fin driven by square wave voltage are calculated. The displacement changes of end nodes are compared, and the swing law under different driving voltage amplitude, frequency, and fluid resistance is analyzed. It is found that the driving efficiency of IPMC can be improved by increasing the driving voltage amplitude, reducing the voltage frequency, and reducing the fluid resistance in a certain range. This research would be beneficial to the study of the large swing motion mechanism of bionic robotic fish.

Fabrication and performance analysis of high-performance cylindrical ionic polymer-metal composite actuators with various diameters

Ionic polymer-metal composites (IPMCs) are electroactive polymer actuators that have been used as artificial muscles and have broad application prospects. In order to further improve the actuation performance of cylindrical IPMCs, Nafion rods with different diameters were prepared by extrusion process, and cylindrical IPMCs with high-quality Pt electrode layers were prepared by electroless plating in this study. The electrochemical properties and actuation performance of cylindrical IPMCs with various diameters were investigated. The tests show that the prepared cylindrical IPMCs have excellent electromechanical properties. As diameter increases, the blocking force and counter back-relaxation ability both increase significantly. Furthermore, the IPMCs with diameter of 3.0 mm under a DC voltage exhibits a superior blocking force (323.9 mN) and excellent power density (up to 139.41 W m−3). Moreover, the thick cylindrical IPMC can lift objects 400 times its weight, demonstrating exceptional load capacity, which shows great prospect of realizing artificial muscles.

Multiday operable ionic polymer-metal composites prepared using a stacking method for practical actuator applications

Ionic polymer-metal composites (IPMCs) with water as an internal solvent (water-IPMCs) lose all their function after 20 min of actuation due to water depletion, despite superb initial performance. Studies have attempted to replace water with ionic liquid (IL), but conventionally made IL-based IPMCs (conventional IL-IPMCs) maintained only a quarter of displacement and blocking force of water-IPMCs. Here, we propose a new method in which a polymer membrane is soaked with IL at high temperatures, and then stacked between two individually-prepared electrode layers. The layers were combined through compression, and the resulting IPMCs (stacked IL-IPMCs) had a surface resistance 10 times lower than conventional IL-IPMCs, and showed actuation performance comparable to water-IPMCs. More importantly, stacked IL-IPMCs maintained more than 95 % of their performance even after several days of actuation. This is a level of stability that has not been reported and therefore a huge breakthrough in the development of IPMC actuators.

Multi-physical modeling and fabrication of high-performance IPMC actuators with serrated interface

Ionic Polymer–Metal Composite (IPMC) has been widely recognized as a promising and representative candidate of soft intelligent materials actuated under low voltage. In the last few years, the importance of the electrode/substrate interface has received growing attention for research on both the modeling of ion-based mass transport and practical performance of the manipulation of ionic electro-active actuators. In this paper, based on a macroscopic serrated interface morphology, the influences of the interface were revealed comprehensively by distinguishing the bending direction as well as the variation of interfacial area, excisional volume and moment of inertia. The offsetting interaction from different aspects were analyzed in detail. On this basis, an interesting result showed that, contrary to current understanding, an enlarged interface area did not necessarily lead to better deformation, which was primarily ascribed to the trade-off of influences from the increasing excisional volume and decreasing bending inertia moment. In addition, a corresponding fabrication process was established, which verified experimentally that IPMC with a super simple macroscopic serrated interface can present a high electro-active performance, providing a minimalist design strategy for ionic electroactive polymer structures.