Ionic Electroactive Polymer Actuators Research Articles

Single-Walled Carbon Nanotube-Reinforced PEDOT: PSS Hybrid Electrodes for High-Performance Ionic Electroactive Polymer Actuator

Ionic electroactive polymer (iEAP) actuators are recognized as exceptional candidates for artificial muscle development, with significant potential applications in bionic robotics, space exploration, and biomedical fields. Here, we developed a new iEAP actuator utilizing high-purity single-walled carbon nanotubes (SWCNTs)-reinforced poly(3, 4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT: PSS, PP) hybrid electrodes and a Nafion/EMIBF4 ion-exchange membrane via a straightforward and efficient spray printing technique. The SWCNT/PP actuator exhibits significantly enhanced electric conductivity (262.9 S/cm) and specific capacitance (22.5 mF/cm2), benefitting from the synergistic effect between SWCNTs and PP. These improvements far surpass those observed in activated carbon aerogel bucky-gel-electrode-based actuators. Furthermore, we evaluated the electroactive behaviors of the SWCNT/PP actuator under alternating square-wave voltages (1–3 V) and frequencies (0.01–100 Hz). The results reveal a substantial bending displacement of 6.44 mm and a high bending strain of 0.61% (at 3 V, 0.1 Hz), along with a long operating stability of up to 10,000 cycles (at 2 V, 1 Hz). This study introduces a straightforward and efficient spray printing technique for the successful preparation of iEAP actuators with superior electrochemical and electromechanical properties as intended, which hold promise as artificial muscles in the field of bionic robotics.

Mechanically Tough Micellar Cubic Liquid‐Crystalline Polymer Electrolytes for Electromechanical Actuators

AbstractThis study presents a novel micellar cubic ionic liquid‐crystalline polymer electrolyte, featuring an alignment‐free spherical structure with unimpeded 3D ionic pathways, aimed at enhancing the performance of an ionic electroactive polymer actuator. The development involved creating a mechanically tough and high ion‐conductive cubic polymer film through the self‐assembly of a wedge‐shaped vinyl imidazolium salt and an imidazolium ionic liquid, followed by in situ photopolymerization. The 300 µm‐thick‐trilayer films, consisting of the cubic polymer electrolyte sandwiched between poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS) electrodes, exhibit remarkable capabilities. These include bearing substantial loads of 4 g with a high blocking force under a DC voltage of 2 V, achieving a high bending strain of 0.63% under a low input voltage (±2 V, 0.1 Hz), and boasting a maximum response frequency of 70 Hz. These properties position the material for potential applications in soft robots and tactile sensing devices.

Modeling and Control of Conducting Polymer Actuator

Conducting polymer (CP) actuator has nonlinear dynamic characteristics during its charge process. In this study, we proposed an electromechanic model and an optimal controller for a type of ionic electroactive polymer (IEPA) actuator with submillimeter scale, which can produce large deformation under low actuation voltage. The electronic model is to describe the evolution of charge state in time domain. The mechanic model is to calculate the deformation of CP actuator under the actuation force and external force. Based on the electromechanic coupling model, a parameter identification method is proposed to estimate the nonlinear parameter of CP actuator. The experiments show that our electromechanic model successfully predicts the deformation of actuator under different input voltages with the identified parameters. In the last step, an optimal controller is designed to control the orientation of IEAP actuator, which achieves at a high control performance in our experiments. The success of the modeling and control lays the foundation work for the subsequent biomedical applications.

Ionic electroactive PEDOT:PSS/liquid-crystalline polymer electrolyte actuators: photopolymerization of zwitterionic columnar liquid crystals complexed with a protic ionic liquid

Ionic electroactive polymer actuators based on photopolymerizable zwitterionic columnar liquid crystals complexed with a protic ionic liquid provided a high bending strain and a large blocking force under a voltage of 2 V.

Highly bendable ionic electroactive polymer actuator based on carboxylated bacterial cellulose by doping with MWCNT

Highly bendable ionic electroactive polymer actuator based on carboxylated bacterial cellulose by doping with MWCNT

Bending Sensor Based on Controlled Microcracking Regions for Application toward Wearable Electronics and Robotics.

A soft bending sensor based on the inverse pyramid structure is demonstrated, revealing that it can effectively suppress microcrack formation in designated regions, thus allowing the cracks to open gradually with bending in a controlled manner. Such a feature enabled the bending sensor to simultaneously have a wide dynamic range of bending strain (0.025-5.4%), high gauge factor (∼74), and high linearity (R2 ∼ 0.99). Furthermore, the bending sensor can capture repeated instantaneous changes in strain and various types of vibrations, owing to its fast response time. Moreover, the bending direction can be differentiated with a single layer of the sensor, and using an array of sensors integrated on a glove, object recognition was demonstrated via machine learning. Finally, a self-monitoring proprioceptive ionic electroactive polymer (IEAP) actuator capable of operating in liquid was demonstrated. Such features of our bending sensor will enable a simple and effective way of detecting sophisticated motion, thus potentially advancing wearable healthcare monitoring electronics and enabling proprioceptive soft robotics.

Effects of Hexagonal Boron Nitride Insulating Layers on the Driving Performance of Ionic Electroactive Polymer Actuators for Light-Weight Artificial Muscles.

To improve the energy efficiency and driving performance of ionic electroactive polymer actuators, we propose inserting insulating layers of 170 nm hexagonal boron nitride (h-BN) particles between the ionic polymer membrane and electrodes. In experiments, actuators exhibited better capacitance (4.020 × 10−1 F), displacement (6.01 mm), and curvature (35.59 m−1) with such layers than without them. The excellent insulating properties and uniform morphology of the layers reduced the interfacial resistance, and the ion conductivity (0.071 S m−1) within the ionic polymer improved significantly. Durability was enhanced because the h-BN layer is chemically and thermally stable and efficiently blocks heat diffusion and ion hydrate evaporation during operation. The results demonstrate a close relationship between the capacitance and driving performance of actuators. A gripper prepared from the proposed ionic electroactive polymer actuator can stably hold an object even under strong external vibration and fast or slow movement.

Smart Bioinspired Actuators: Crawling, Linear, and Bending Motions through a Multilayer Design.

To fulfill the insatiable demand for wearable technologies, ionic electroactive polymer actuators have been entrenched as promising candidates that can convert low-input-voltage energy into high mechanical throughput. However, a ubiquitous trilayer design of actuators allows exclusively bending deformation and their highly nonlinear response restricts the true potential of low-voltage actuators for next-generation technology. Herein, we report an unprecedented multilayer design for soft actuators that enables complex deformations shown by skeletal muscles, mechanoreceptors, and plant roots in response to various environmental stimuli. Hierarchically ordered pores in a stretchable interlayer provide excellent electromechanical properties and fast charging kinetics, which enable linear motion by soft actuators at 3 V and under ambient conditions. Our actuators demonstrate astonishing levels of performance, including a 6.5% linear actuation strain, 0.8 s rapid switching speed, and 5000 cycle stable performance in air, producing a 4.2 mN linear blocking force at a ±3 V alternating square-wave voltage. This actuator design demonstrating a walkable spider capable of controlled back-and-forth propelling motion at low driving voltages provides the platform to envision a complex functionality using a portable battery as a power source for soft robotics, wearable exosuits, and biomimetic technologies.

A Kirigami Approach of Patterning Membrane Actuators.

Ionic electroactive polymer actuators are typically implemented as bending trilayer laminates. While showing high displacements, such designs are not straightforward to implement for useful applications. To enable practical uses in actuators with ionic electroactive polymers, membrane-type film designs can be considered. The significantly lower displacement of the membrane actuators due to the lack of freedom of motion has been the main limiting factor for their application, resulting in just a few works considering such devices. However, bioinspired patterning designs have been shown to significantly increase the freedom of motion of such membranes. In this work, we apply computer simulations to design cutting patterns for increasing the performance of membrane actuators based on polypyrrole doped with dodecylbenzenesulfonate (PPy/DBS) in trilayer arrangements with a polyvinylidene fluoride membrane as the separator. A dedicated custom-designed device was built to consistently measure the response of the membrane actuators, demonstrating significant and pattern-specific enhancements of the response in terms of displacement, exchanged charge and force.

Consistent response from conducting polymer actuators: Potential window and embedded charges to avoid mixed ion transport

A soft ionic electroactive polymer actuator does not differ from other types of actuators in the requirement of reliable, controllable and consistent performance. In ionic systems, like those of conducting polymers, the direction of actuation (as well as - naturally - the amplitude) depends on the dominance of one type of ions (cations over anions or vice versa) as the mobile species, maintaining charge neutrality. Here we demonstrate that the same polypyrrole (PPy) films can have rather different response in terms of linear actuation amplitude as well as direction under different voltage ranges. A system designed to mitigate such uncertainties – PPy blended with polymerized ionic liquid – is shown as a comparison. Three reversible and charge-balanced potential ranges in cyclic voltammetry and square wave voltage steps experiments were chosen to demonstrate the importance of selecting the right voltage range, especially if no embedded charges acting as “filters” are being used.

Integrating Ionic Electroactive Polymer Actuators and Sensors Into Adaptive Building Skins – Potentials and Limitations

Building envelopes separate the confined interior world engineered for human comfort and indoor activity from the exterior world with its uncontainable climatic forces and man-made immission. In the future, active, sustainable and lightweight building skins are needed to serve as an adaptive interface to govern the building-physical interactions between these two worlds. This article provides conceptual and experimental results regarding the integration of ionic electroactive polymer sensors and actuators into fabric membranes. The ultimate goal is to use this technology for adaptive membrane building skins. These devices have attracted high interest from industry and academia due to their small actuation voltages, relatively large actuation and sensing responses and their flexible and soft mechanical characteristics. However, their complex manufacturing process, sophisticated material compositions and their environmental sensitivity have limited the application range until now. The article describes the potentials and limitations of employing such devices for two different adaptive building functionalities: first, as a means of ventilation control and humidity regulation by embedding small actuated apertures into a fabric membrane, and second, as flexible, energy- and cost-efficient distributed sensors for external load monitoring of such structures. The article focusses on designing, building and testing of two experimental membrane demonstrators with integrated polymer actuators and sensors. It addresses the challenges encountered and draws conclusions for potential future optimization at the device and system level.

Poly(3,4-ethylene dioxythiophene):Poly(styrene sulfonate)-Functionalized Reduced Graphene Oxide Electrode for Ionic Electroactive Polymer Actuators

Ionic electroactive polymer (IEAP) actuators, which offer advantages such as reduced device weight, flexibility, and large deformation under low voltages (1–5 V), have found utility in applications such as biomimetic robots, actuators, and sensors. In this context, in this study, we fabricate poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate)-reduced graphene oxide (PEDOT:PSS-rGO) composite paper electrodes for actuator application. PEDOT:PSS-rGO paper electrodes are prepared by vacuum filtration of a PEDOT:PSS-rGO mixture that is subsequently subjected to heat treatment under an argon atmosphere via furnace annealing. We find that a 5:1 weight ratio of PEDOT:PSS-GO provides the lowest sheet resistance. We next fabricate a PEDOT:PSS-rGO actuator via filtration and the hot-pressing method with rGO paper electrodes, which have hydrophobic properties and low liquid permeability that effectively prevents water evaporation, and we examine its actuating performance. Our results indicate that after functionalization with PEDOT:PSS, the electrical properties and surface roughness of PEDOT:PSS-rGO composite paper electrode are improved. Further, the mechanical properties of the IEAP actuator based on the PEDOT:PSS-rGO paper electrodes exhibits enhanced performance by a factor of 4 relative to an actuator with conventional rGO electrodes.

Effect of Ionic Polymer Membrane with Multiwalled Carbon Nanotubes on the Mechanical Performance of Ionic Electroactive Polymer Actuators.

Ionic electroactive polymer (IEAP) actuators have received interest because of their advantageous properties, including their large displacement, high energy density, light weight, and low power consumption under a low electric field. However, they have a low blocking force under driving, and it is difficult to control the thickness of the ionic polymer membrane. In this study, an IEAP actuator is fabricated using a Nafion membrane with added multiwalled carbon nanotubes to increase the blocking force. A heat press two-step process is also developed to produce a constant and uniform membrane. The fabricated Nafion membrane with 0.2 wt% multiwalled carbon nanotubes has the largest displacement and highest blocking force. As a result, the developed heat press two-step method can be used in various polymer-casting fields, and the fabricated carbon nanotube-based IEAP actuators can serve as useful references in fields such as flexible robotics and artificial muscles.

Ionic electro-active polymer actuator based on cobalt-containing nitrogen-doped carbon/conducting polymer soft electrode

Nanoscale cobalt-containing nitrogen-doped porous carbon (CoNC) materials were prepared by thermolysis of a zeolitic imidazolate framework (ZIF), ZIF-67, at different temperatures and their application for ionic electro-active polymer (EAP) actuator was evaluated. CoNC-700, which was obtained from ZIF-67 pyrolysis at 700 °C, exhibits specific surface area of 753.86 m2 g−1, pore volume of 0.5768 cm3 g−1, and specific capacitance of 120.7 F∙g−1. CoNC/conducting polymer soft electrode were fabricated by unitizing effective interaction of CoNC with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). High-performance ionic actuators were developed for the first time using this CoNC/PEDOT:PSS soft electrode. The developed ionic EAP actuator exhibited large peak-to-peak displacement of 20.4 mm and high bending strain of 0.28% (3 V and 0.1 Hz). Therefore, ZIFs or metal organic frameworks (MOFs) can be applied to provide significant improvements in EAP actuators, which can play key roles as technological advances toward bioinspired actuating devices required for next-generation soft and wearable electronics.

Controllable and durable ionic electroactive polymer actuator based on nanoporous carbon nanotube film electrode

Ionic electroactive polymer (iEAP) actuators have attracted great attention in the fields of micro-electromechanical systems and biomedicine due to their remarkably large strain under low-voltage stimulation. As actuation performance is mainly dominated by the electrochemical and electromechanical processes, the electrode layer and its structure are increasingly crucial to the actuators. In this research, we introduced a nanoporous carbon nanotube film with superior conductivity (1000–2000 S cm−1) as a cost-effective alternative electrode in fabricating iEAP actuators. The actuators were assembled by hot-pressing a Nafion/EMImBF4 electrolyte layer between two electrode films under vacuum conditions. Based on the developed porous hierarchal structure and superior electrical and mechanical properties of the electrode film, the actuators showed highly improved electrochemical and electromechanical properties and can operate controllably and durably under various voltage amplitudes and waveforms with a wide frequency range. The generated strain and stress reach up to 1.26% and 5.27 MPa, respectively, which are greater than the performances of the actuators based on polymer-supporting nano carbon electrodes. Once the voltage increases by 1 V, the strain and stress will increase by 0.336% and 1.407 MPa, respectively. The actuators can perform more than 20 000 cycles with an initial drop less than 20% in the operation stroke, showing a relatively durable and controllable cycle life. The newly developed actuators can be promising candidates for artificial muscles in academic interest and industrial applications.

Encapsulation of ionic electromechanically active polymer actuators

Biomimetic movement and low operating voltage have made ionic electroactive polymer actuators (iEAPs) interesting for applications where interactions with living organisms occur, such as haptic devices operating mainly in air or minimally invasive or chronically implanted medical devices operating in biological fluids. However, not all materials that are typically used in the fabrication of iEAPs are biofriendly, nor are the biological environments with various electrolyte compositions safe or optimal for the actuator. This paper presents a comprehensive overview of materials and methods that have been previously used to encapsulate ionic electroactive polymer actuators. Recently, increasing emphasis has been given to the miniaturization of actuators for the biomedical field, and therefore in the detailed overview we have focused on automated, tunable and industrially applicable coating methods, together with promising biocompatible encapsulant materials. In the final section, we introduce a carbon-based actuator that has been dip-coated with polydimethylsiloxane elastomer that shows extended lifetime during actuation in water.

Enhanced Stability and Driving Performance of GO⁻Ag-NW-based Ionic Electroactive Polymer Actuators with Triton X-100-PEDOT:PSS Nanofibrils.

Ionic electroactive polymers (IEAPs) have received considerable attention for their flexibility, lightweight composition, large displacement, and low-voltage activation. Recently, many metal–nonmetal composite electrodes have been actively studied. Specifically, graphene oxide–silver nanowire (GO–Ag NW) composite electrodes offer advantages among IEAPs with metal–nonmetal composite electrodes. However, GO–Ag NW composite electrodes still show a decrease in displacement owing to low stability and durability during driving. Therefore, the durability and stability of the IEAPs with metal–nonmetal composite electrodes must be improved. One way to improve the device durability is coating the electrode surface with a protective layer. This layer must have enough flexibility and suitable electrical properties such that it does not hinder the IEAPs’ driving. Herein, a poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS) protective layer and 4-(1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol (Triton X-100) are applied to improve driving performance. Triton X-100 is a nonionic surfactant that transforms the PEDOT:PSS capsule into a nanofibril structure. In this study, a mixed Triton X-100/PEDOT:PSS protective layer at an optimum weight ratio was coated onto the GO–Ag NW composite-electrode-based IEAPs under various conditions. The IEAP actuators based on GO–Ag NW composite electrodes with a protective layer of PEDOT:PSS treated with Triton X-100 showed the best stability and durability.

Comparative Analysis of Fluorinated Anions for Polypyrrole Linear Actuator Electrolytes.

Either as salts or room temperature ionic liquids, fluorinated anion-based electrolytes have been a common choice for ionic electroactive polymer actuators, both linear and bending. In the present work, propylene carbonate solutions of four electrolytes of the three hugely popular anions—triflouromethanesulfonate, bis(trifluoromethane)sulfonimide, and hexafluorophosphate were compared and evaluated in polypyrrole linear actuators. The actuation direction, the characteristics—performance relations influence the behavior of the actuators. Isotonic Electro-chemo-mechanical deformation (ECMD) measurements were performed to study the response of the PPy/DBS samples. The highest strain for pristine PPy/DBS linear actuators was found in range of 21% for LiTFSI, while TBAPF6 had the least cation involvement, suggesting the potential for application in durable and controllable actuators. Interesting cation effects on the actuation of the same anions (CF3SO3−) were also observed.

An Ionic Polymer Actuator Capable of Simultaneously Improving Bandwidth and Blocking Force for Efficient Haptic Feedback

Recently, an ionic electroactive polymer (i-EAP) actuators are spotlighted in various fields because they provide a lot of advantages such as lightweight, flexibility, simple process, and low driving power. However, they suffer from low blocking force, displacement, and wide bandwidth that can be implemented under electric field for apply to various applications. In order to apply these i-EAP actuators to various applications, it is important to provide the optimum characteristics of the i-EAP actuator adaptive to the target application. Particularly, it is required to achieve high blocking force and displacement as well as wide actuation bandwidth for haptic feedback among the various applications. In this talk, we propose an ionic polymer actuator (IPA) with wide bandwidth of over 100Hz and high blocking force based on PEDOT:PSS electrode with additives and ionic polymer with fibrillary nanostructures for effective haptic feedback. In particular, we developed an actuator that improves the interfacial properties between electrodes and an ionic polymer as well as electrical conductivity of electrodes by simple and effective way through spray-coating of PEDOT: PSS solution with additives. As a result, the IPA was successfully operated with a large displacement up to 2.5mm at an operating frequency of 20mHz under an applied voltage of 2V. Further, the IPA shows large blocking force of 0.4mN at operating frequency of 1Hz. These our actuator is capable of driving up to a high frequency of 200Hz and shows an improved blocking force up to 0.4mN. We potentially believe our IPA will provide a rational guide to future haptic feedback.

Fast and Stable Ionic Electroactive Polymer Actuators with PEDOT:PSS/(Graphene⁻Ag-Nanowires) Nanocomposite Electrodes.

Ionic electroactive polymer (IEAP) actuators that are driven by electrical stimuli have been widely investigated for use in practical applications. However, conventional electrodes in IEAP actuators have a serious drawback of poor durability under long-term actuation in open air, mainly because of leakage of the inner electrolyte and hydrated cations through surface cracks on the metallic electrodes. To overcome this problem, a top priority is developing new high-performance ionic polymer actuators with graphene electrodes that have superior mechanical, electrical conductivity, and electromechanical properties. However, the task is made difficultby issues such as the low electrical conductivity of graphene (G). The percolation network of silver nanowires (Ag-NWs) is believed to enhance the conductivity of graphene, while poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), which exhibits excellent stability under ambient conditions, is expected to improve the actuation performance of IEAP actuators. In this study, we developed a very fast, stable, and durable IEAP actuator by employing electrodes made of a nanocomposite comprising PEDOT:PSS and graphene–Ag-NWs (P/(G–Ag)). The cost-effective P/(G–Ag) electrodes with high electrical conductivity displayed a smooth surface resulting from the PEDOT:PSS coating, which prevented oxidation of the surface upon exposure to air, and showedstrong bonding between the ionic polymer and the electrode surface. More interestingly, the proposed IEAP actuator based on the P/G–Ag electrode can be used in active biomedical devices, biomimetic robots, wearable electronics, and flexible soft electronics.