Conducting Polymer Actuators Research Articles

Wireless Coupling of Conducting Polymer Actuators with Light Emission.

Combining the actuation of conducting polymers with additional functionalities is an interesting fundamental scientific challenge and increases their application potential. Herein we demonstrate the possibility of direct integration of a miniaturized light emitting diode (LED) in a polypyrrole (PPy) matrix in order to achieve simultaneous wireless actuation and light emission. A light emitting diode is used as a part of an electroactive surface on which electrochemical polymerization allows direct incorporation of the electronic device into the polymer. The resulting free-standing polymer/LED hybrid can be addressed by bipolar electrochemistry to trigger simultaneously oxidation and reduction reactions at its opposite extremities, leading to a controlled deformation and an electron flow through the integrated LED. Such a dual response in the form of actuation and light emission opens up interesting perspectives in the field of microrobotics.

Model-free control of an electro-active polymer actuator

Conducting polymer actuators (CPAs) are promising candidates for replacing conventional actuators due to their advantageous properties such as low cost, low weight, small actuation voltage and biocompatibility. One of the obstacles for these actuators to become widespread in real world applications is the difficulty of controlling their position or force output as these actuators represent time varying and nonlinear dynamics due to various effects such as synthesis process and conditions, changes in ambient conditions, etc. Linear models are of limited use to design controllers for them since the performance of these controllers may not be sufficient due to model mismatches. Especially, due to their time varying behaviour, a pre-designed controller based on an identified model may show performance deterioration in time. In this study, a model-free control framework is proposed to control the tip displacement of a trilayer conducting polymer actuator with polypyrrole electrodes. The proposed control strategy eliminates the requirement of identification of the dynamics of CPAs for each application and is based on fast derivative estimation of noisy signals. Another advantage of the method is that it is very simple to design and implement. Experimental results are obtained for the model free control method and compared with those of classical PI control.

Improved charging and strain rates by laser perforating polypyrrole actuator electrodes

Conducting polymer actuators generate significant strains (1%–10%) when driven at low voltages, and are muscle-like in their linear deformation, mechanical compliance, silent operation, and energy density. However, slow electrochemical processes have hindered widespread application. To operate electroactive polymer actuators in practical applications such as soft robotics, the speed of energy delivery is often important. Recent work has achieved very fast actuation by using very thin films and blending of materials of high ionic conductivity with conducting polymers, allowing fast insertion of ions. Here we make microscopic arrays of holes in relatively thick, easy to handle conducting polymer films in order to speed ion insertion and actuation. A single-step, top-down, non-contact and template-free approach is used, employing femto and picosecond lasers to texturize polypyrrole based actuators while preserving the stress and strain output. A wide range of hole separations and diameters (pitch/diameter from 9.75/5.17 μm to 24.7/13.2 μm) are explored to reduce the ion diffusion path length in the bulk polymer. This led to a speed increase of between 2 and 30 times. A finite element model based on diffusion shows similar improvements, suggesting that the reduced distance of mass transport achieved by laser perforation is the key to faster response times in the thick electrodes used. The demonstrated ability to increase rate of response using micromachined electrodes is potentially applicable to batteries and supercapacitors.

Nonlinear dynamic modeling of ultrathin conducting polymer actuators including inertial effects

Trilayer conducting polymer (CP) actuators are potential alternatives to piezoelectric and electrostatic actuators due to their large strain, and recently demonstrated operation at hundreds of Hertz. However, these actuators exhibit nonlinear electrical and mechanical properties as a function of their oxidation state, when operated over their full strain range, making it more challenging to accurately predict their mechanical behavior. In this paper, an analytical multi-physics model of the CP actuators is proposed to predict their nonlinear dynamic mechanical behavior. To demonstrate the accuracy of the model, a trilayer actuator composed of a solid polymer electrolyte sandwiched between two poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes was fabricated and characterized. This system consists of an electrical subsystem represented by an RC equivalent circuit, an electro-mechanical coupling matrix, and a mechanical subsystem described by using a rigid finite element method. The electrical conductivity and the volumetric capacitance, an empirical strain-to-charge ratio, and Young’s modulus of the actuator as a function of the PEDOT electrode charge state were also implemented into the model, using measured values. The proposed model was represented using a bond graph formalism. The concordance between the simulations and the measurements confirmed the accuracy of the model in predicting the nonlinear dynamic electrical and mechanical response of the actuators. In addition, the information extracted from the model also provided an insight into the critical parameters of the actuators and how they affect the actuator efficiency, as well as the energy distribution including dissipated, stored, and transferred energy. These are the key parameters for designing, optimizing, and controlling the actuation behavior of a trilayer actuator.

Polypyrrole actuators: the effects of polymer thickness and voltage scan rate on fractional charging and isotonic actuation strain

For conducting polymer actuators to be practically useful, they need to be able to generate large forces and displacements and respond quickly. The simplest way to generate larger forces is to produce thicker actuators, but this approach has a negative impact on the response time. The effects of polypyrrole film thickness and voltage scan rate on the electrochemical actuation strain rate are investigated in this study. The rate of oxidative charging is shown to follow a standard Fickian diffusion model suggesting that the migration of ions into the polymer from the electrolyte is the dominant rate-determining mechanism. The migration rate is slow with full oxidation requiring several minutes for film thicknesses of just 10 μm. The free strains generated were found to be directly proportional to the oxidative charge passed. The isotonic actuation strains were additionally reduced by increasing applied stress and this effect was attributed to the increase in Young’s modulus that occurs during polypyrrole oxidation. A simple model is presented that predicts the change in modulus during oxidation and gives reasonable estimates of the isotonic actuation for PPy actuators of different thickness and when subjected to different stresses.

Ultrathin electrochemically driven conducting polymer actuators: fabrication and electrochemomechanical characterization

Electronic conducting polymer based-actuators have attracted lots of interest as alternative materials to traditional piezoelectric and electrostatic actuators. Their specific characteristics such as their low operating voltages and large strains should allow them to adapt better to soft microstructures. Recently, poly (3,4-ethylenedioxythiophene) (PEDOT) – based ionic actuators have overcome some initial stumbling blocks to widespread applications in the microfabricated devices field. These trilayer bending microactuators were fabricated (i) by sequential stacking, using a layer by layer polymerization (LbL) of conducting polymer electrodes and a solid polymer electrolyte and (ii) by micro-patterning, using standard microsystems processes. While microfabrication processing of a trilayer actuator, involving no manual handling has been demonstrated, their bending performances remain limited for practical applications. Moreover, the complete characterization of their electrical, electrochemical, and mechanical properties has never been investigated. This paper describes the optimization of PEDOT electroactive electrodes synthesized with a vapor phase polymerization process. Influence of synthesis parameters on thickness, electronic conductivity and volumetric charge density were studied to determine the guidelines for synthesizing highly efficient electrodes. Afterwards, these parameters are used to guide the LbL synthesis process of ultrathin trilayer actuators. Electrochemical and mechanical properties of the resulting microactuators have been thoroughly characterized. Bending deformation and output force generation have been measured and reached 0.5% and 11 μN respectively. This constitutes the first characterization of ionic PEDOT-based microactuators operating in air of such a thin thickness (11 μm dry and 18.3 μm swelled in 1-Ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMImTFSI)). These actuators and their actuation properties are promising for future soft microsystem devices where the use of polymer actuators should be essential.

Muscle Coordination Control and Hysteresis of a 1 DOF Antagonistic Driven System Using Conductive Super-Coiled Polymer Actuators

Muscle Coordination Control and Hysteresis of a 1 DOF Antagonistic Driven System Using Conductive Super-Coiled Polymer Actuators

Design and Control of an Antagonistic Driven System With a Joint Mechanism Increasing the Rotational Angle Using Conductive Super-Coiled Polymer Actuators

Design and Control of an Antagonistic Driven System With a Joint Mechanism Increasing the Rotational Angle Using Conductive Super-Coiled Polymer Actuators

Thin ink-jet printed trilayer actuators composed of PEDOT:PSS on interpenetrating polymer networks

Abstract Mass production of conducting polymer actuators with reliable performance is envisaged in the field of artificial muscles. In this study, inkjet printing and spin coating – two established technologies for large-scale production – were combined for microactuator fabrication. Actuators based on poly(3,4-ethylenedioxy-thiophene):poly(styrene sulfonate) electrodes (PEDOT:PSS, 2.2 μm thick, 190 S cm−1), which were inkjet-printed onto a spin-coated membrane of an interpenetrating polymer network (IPN) thin film composed of nitrile butadiene rubber and poly(ethylene oxide) (PEDOT:PSS-IPN-PEDOT:PSS) with a total thickness of 12.7 μm, were prepared and studied. Our goal was to investigate the performance of the trilayers in linear actuation, in aqueous and organic (propylene carbonate) solutions of bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) used as electrolytes, and in bending actuation in air using an ionic liquid as the electrolyte. Electro-chemo-mechanical deformation (ECMD) measurements were consistent with electrochemical measurements showing a strain of 3% in aqueous electrolyte and 1% in propylene carbonate. A strain of 0.14% in the bending mode in the ionic liquid was observed due to electric double layer charging, while in electrolyte solutions, redox reactions determined the linear actuation properties. In the aqueous electrolyte, a specific capacitance of 193 F g−1 was measured for the printed PEDOT:PSS films, with potential for applications in supercapacitors.

Digital light processing for the fabrication of 3D intrinsically conductive polymer structures

Conventional methods to fabricate intrinsically conductive polymer actuators result in planar morphologies that limit fabricated devices to simplistic linear or bending actuation modes. In this study, we report a conductive polymer formulation and associated 3D printing fabrication method capable of realizing three-dimensional conductive polymer structures that are not subject to such geometric limitations. A light-based 3D printing technique known as digital light processing is employed due to its ability to fabricate complex microscale features in conjunction with a specially-formulated photosensitive polypyrrole resin. The performance of this fabrication system is characterized via feature resolution and depth of cure experiments, and the results are subsequently applied to the fabrication of 3D components. This technique enables the fabrication of novel electroactive polymer structures and provides a framework for advanced 3D electroactive polymer-enabled devices capable of complex modes of sensing and actuation.

Biocompatible silk-conducting polymer composite trilayer actuators

Biocompatible materials capable of controlled actuation are in high demand for use in biomedical applications such as dynamic tissue scaffolding, valves, and steerable surgical tools. Conducting polymer actuators are of interest because they operate in aqueous electrolytes at low voltages and can generate stresses similar to natural muscle. Recently, our group has demonstrated a composite material of silk and poly(pyrrole) (PPy) that is mechanically robust, made from biocompatible materials, and bends under an applied voltage when incorporated into a simple bilayer device architecture and actuated using a biologically relevant electrolyte. Here we present trilayer devices composed of two silk-PPy composite layers separated by an insulating silk layer. The trilayer architecture allows one side to expand while the other contracts, resulting in improved performance over bilayer devices. Specifically, this configuration shows a larger angle of deflection per volt applied than the analogous bilayer system, while maintaining a consistent current response throughout cycling. In addition, the overall motion of the trilayer devices is more symmetric than that of the bilayer analogs, allowing for fully reversible operation.

Nonlinear Two-Dimensional Transmission Line Models for Electrochemically Driven Conducting Polymer Actuators

The electronic and ionic conductivities of conducting polymers can change as a function of oxidation state, and yet, these properties are not generally considered in modeling the electrochemistry and electrochemically driven actuation of these materials. These effects can be significant particularly over large ranges of oxidation state and in long films where electrical contact is made from one end. In this study, a transmission line model is implemented, in which conductivities vary as a function of local oxidation state, with this variation being based on measured values. Our time-domain model is based on a 2-D RC transmission line model implemented using a state-space representation. Voltage drop along the length of the film away from the attachment point and the variation in electronic conductivity with state of charge along this length necessitated the use of a 2-D nonlinear model to obtain effective predictions of response for the film dimension used. The general approach demonstrated may be applied to any situation where properties vary with position and oxidation state, such as in batteries and supercapacitors. The last step showed the successful application of the model to predict actuation of a polypyrrole linear actuator.

Air-operating polypyrrole actuators based on poly(vinylidene fluoride) membranes filled with poly(ethylene oxide) electrolytes

To develop air-operating conducting polymer (CP) actuators with enhanced performance, polymer electrolyte membranes with high ionic conductivity and mechanical endurance are necessary. Poly(ethylene oxide) oligomers penetrate into porous poly(vinylidene fluoride) membranes and sequentially undergo crosslinking to produce polymer electrolyte membranes. The properties of the electrolyte membranes are regulated by varying the degree of crosslinking. Polypyrrole layers are constructed on the surfaces of the membranes by chemical polymerization, creating CP actuators. CP actuators based on the resulting polymer electrolyte membranes operate properly in air and show highly enhanced performance such as a large displacement and long operation time. This approach, therefore, has great potential to extend the applications of CP actuators.

High energy conversion efficiency conducting polymer actuators based on PEDOT:PSS/MWCNTs composite electrode

High performance actuator with large deformation and high conversion efficiency.

Self-contained tubular bending actuator driven by conducting polymers

The low voltage operation and relatively high strain response of conducting polymer actuators has made their use in tubular actuators such as actively steerable catheter tips of interest. Previous work has shown that bending can be achieved by simply coating a commercial catheter with conducting polymer and patterning. However, these actuators require an external electrolyte to operate. This work presents instead a self-contained tubular actuator in which all ion conduction between active polymer layers occurs internally.The conducting polymer PEDOT provides the active deformation to control its maneuverability and actuation. To form the body of the actuator and an electrolyte medium to enable transfer of ions during the actuation of conducting polymer, a highly ionically conductive interpenetrating polymer network composed of ionically conductive polyethylene oxide and stretchable nitrile butadiene rubber (NBR) is used. This compliant medium also enables a tight radius of curvature. Laser micromachining is used to pattern PEDOT on the surface. A 0.95mm diameter device is shown to achieve a 22mm radius of curvatures under activation of 2V. A closed form beam bending model for tubular trilayer actuators is derived which predicts the radius of curvature as a function of applied voltage and free strain. This model enables easy prediction of deflection, as is demonstrated.

Research Trends of Soft Actuators based on Electroactive Polymers and Conducting Polymers

Artificial muscles (or soft actuators) based on electroactive polymers (EAPs) are attractive power sources to drive human-like robots in place of electrical motor, because they are quiet, powerful, light weight and compact. Among EAPs for soft actuators, conducting polymers are superior in strain, stress, deformation form and driving voltage compared with the other EAPs. In this paper, the research trends of EAPs and conducting polymers are reviewed by retrieval of the papers and patents. The research activity of EAP actuators showed the maximum around 2010 and somehow declining now days. The reasons for the reducing activity are found to be partly due to problems of conducting polymer actuators for the practical application. The unique characteristics of conducting polymer actuators are mentioned in terms of the basic mechanisms of actuation, creeping, training effect and shape retention under high tensile loads. The issues and limitation of conducting polymer soft actuators are discussed.

Bottom-up microfabrication process for individually controlled conjugated polymer actuators

Handling of soft and fragile sub-millimeter sized samples such as cells and tissues requires new tools that allow delicate manipulation. Conducting polymer actuators show unique characteristics suitable to driving such manipulators, however despite their potential, the current fabrication method of the trilayer structures does not allow constructing advanced micromanipulators operating in air using this technology. Here we show a novel bottom-up microfabrication process for conjugated polymer trilayer actuators using various solid polymer electrolytes. In addition, the process design integrates contact pads, which has been an issue for small scale conducting polymer actuators. The microfabrication process starts with a patterned layer of conjugated polymer, followed by depositing a polymer electrolyte and a second patterning of the second conjugated polymer layer. The process resulted in successful fabrication of individually controllable conducting polymer trilayer actuators comprising polyvinylidenefluoride and poly(vinylidenefluoride-co-hexafluoropropylene) membranes and showed good interfacial adhesion between the different layers in the final device. The polyvinylidenefluoride trilayer actuator showed good actuation capability. The developed bottom-up microfabrication method paves the way for the development of novel micromanipulation tools.

Towards inkjet printable conducting polymer artificial muscles

Inkjet printing is a key technology in the field of defined polymer deposition as well as in fabrication of strain sensors. It is also one of the most promising alternatives to prevalent fabrication of conducting polymer actuators. Nevertheless, inkjet printed actuators were not yet realised due to rheological properties of conducting polymer solutions that challenge jetting and the complex solution–membrane interactions, that lead to poor adhesion or uncontrolled infiltration. In order to enable this fabrication method, hybrid hydrophilic-hydrophobic polyvinylidene fluoride (PVDF) ultrafiltration membranes were used. They ensure good adhesion with printed poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) layer. Furthermore, PEDOT:PSS compositions that have liquid properties suitable for printing but do not cause uncontrolled infiltration through the membrane were identified. This allowed the realisation of the first inkjet printed PEDOT:PSS based ionic actuators working in air.

Top-down Approach for the Direct Synthesis, Patterning, and Operation of Artificial Micromuscles on Flexible Substrates.

Recent progress in the field of microsystems on flexible substrates raises the need for alternatives to the stiffness of classical actuation technologies. This paper reports a top-down process to microfabricate soft conducting polymer actuators on substrates on which they ultimately operate. The bending microactuators were fabricated by sequentially stacking layers using a layer polymerization by layer polymerization of conducting polymer electrodes and a solid polymer electrolyte. Standalone microbeams thinner than 10 μm were fabricated on SU-8 substrates associated with a bottom gold electrical contact. The operation of microactuators was demonstrated in air and at low voltage (±4 V).

An Electrolyte-Free Conducting Polymer Actuator that Displays Electrothermal Bending and Flapping Wing Motions under a Magnetic Field.

Electroactive materials that change shape in response to electrical stimulation can serve as actuators. Electroactive actuators of this type have great utility in a variety of technologies, including biomimetic artificial muscles, robotics, and sensors. Electroactive actuators developed to date often suffer from problems associated with the need to use electrolytes, slow response times, high driving voltages, and short cycle lifetimes. Herein, we report an electrolyte-free, single component, polymer electroactive actuator, which has a fast response time, high durability, and requires a low driving voltage (<5 V). The process employed for production of this material involves wet-spinning of a preorganized camphorsulfonic acid (CSA)-doped polyaniline (PANI) gel, which generates long, flexible, and conductive (∼270 S/cm) microfibers. Reversible bending motions take place upon application of an alternating current (AC) to the PANI polymer. This motion, promoted by a significantly low driving voltage (<0.5 V) in the presence of an external magnetic field, has a very large swinging speed (9000 swings/min) that lies in the range of those of flies and bees (1000-15000 swings/min) and is fatigue-resistant (>1000000 cycles).