Electroactive Polymer Research Articles

Modeling of an electro-active pseudo-trilayer based on PEDOT, a semi-conductor polymer

Abstract Electroactive polymers are smart materials that can be used as actuators, sensors, or energy harvesters. We focus on a pseudo trilayer based on PEDOT, a semiconductor polymer: the central part consists of two interpenetrating polymers and PEDOT is polymerized on each side; the whole blade is saturated with an ionic liquid. A pseudo trilayer is obtained, the two outer layers acting as electrodes. When an electric field is applied, the cations move towards the negative electrode, making it swell, while the volume decreases on the opposite side; this results in the bending of the strip. Conversely, the film deflection generates an electric potential difference between the electrodes. We model this system and establish its constitutive relations using the thermodynamics of irreversible processes; we obtain a Kelvin–Voigt stress–strain relation and generalized Fourier’s and Darcy’s laws. We validate our model in the static case: we apply the latter to a cantilever blade subject to a continuous potential electric difference at the constant temperature. We draw the profiles of the different quantities and evaluate the tip displacement and the blocking force. Our results agree with the experimental data published in the literature.

Piezoelectric properties and microstructural changes of smart asphalt-based composites containing electroactive polymer and carbon black

The requirements for smart asphalt pavement with piezoelectric properties are becoming necessary as the demand for clean energy and intelligent transportation are increased. To develop asphalt-based composite with electroactive performance for pavement electricity generation and to recycle battery waste, carbon black was first added to polyvinylidene fluoride-hexafluoropropylene to prepare electroactive polymer modifier (EPM) with high content of electroactive crystalline phases. Then carbon black and EPM were added into asphalt to prepare asphalt-based composites containing electroactive polymer (ACEP). The Output voltage, environmental scanning electron microscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray diffraction and basic performance tests were conducted to study the piezoelectric properties, microstructural changes, electroactivity generation mechanism and basic performance of ACEP. The result shows that 5 % EPM has good dispersion, and stable crystallization rate of about 26 % and considerable electroactive crystalline phase content in asphalt, but more holes and defects inside ACEP appears when EPM is excessive. Also, the addition of EPM can slightly improve low-temperature property and thermal stability of ACEP. This is because the F element in EPM can interact with the polar groups in the gum and asphaltene. The 5 % ACEP sample with a thickness of 5 mm can output a voltage of about 260 mV. The penetration, ductility and softening point of 5 % ACEP were 55.2 dmm, 285 mm and 62.3°C, respectively. It is found that ACEP has a good combination of piezoelectric and basic pavement properties and can be used to build smart asphalt pavement with piezoelectric properties. This also provides a way to recycle battery waste.

An investigation of the electrical dynamics in electroactive polymer transducers with resistive electrodes

To pursue a variable-capacitance working principle, transducers based on soft electroactive polymers (EAPs) need deformable electrodes that match the compliance and stretchability of the EAP polymeric substrates. A variety of manufacturing procedures are available to create conductive materials that can achieve this, including solutions that can provide remarkably low resistivity. However, the simplest and most feasible options often involve the use of particle-filled (e.g. carbon-filled) polymer composites, which, while easy to produce, tend to exhibit relatively high resistivity. This high level of resistivity, combined with the inherent capacitance of EAP transducers, introduces dynamic effects in the devices electrical activation, which may affect performance. This paper investigates the impact of electrode resistivity on the electrical dynamics of EAP devices, combining continuum models and experimental validations. We use a continuum generalisation of known resistive-capacitive (RC) transmission line models to accurately predict voltage gradients on the surfaces of electrostatic transducers subject to rapidly varying voltages. We then present an experimental validation by measuring the spatial voltage distributions over carbon-based polymeric electrodes of dielectric elastomer (DE) transducers, and find a good agreement with our model predictions. We use our validated model to provide general estimates of the typical charging time and limit working frequency ranges of DE devices as a function of their dimensional scale and electrode sheet resistance. Our model provides useful indications for designing compliant electrodes in EAP transducers given target performance, or to understand the working limits of devices with given geometry and dielectric-electrode properties.

Soft electroactive polymer actuators based on regioregular/regiorandom-poly(3-hexylthiophene) blends with a nanofiber structure

Soft electroactive polymer actuators based on regioregular/regiorandom-poly(3-hexylthiophene) blends with a nanofiber structure

Ingenious Structure Engineering to Enhance Piezoelectricity in Poly(vinylidene fluoride) for Biomedical Applications.

The future development of wearable/implantable sensing and medical devices relies on substrates with excellent flexibility, stability, biocompatibility, and self-powered capabilities. Enhancing the energy efficiency and convenience is crucial, and converting external mechanical energy into electrical energy is a promising strategy for long-term advancement. Poly(vinylidene fluoride) (PVDF), known for its piezoelectricity, is an outstanding representative of an electroactive polymer. Ingeniously designed PVDF-based polymers have been fabricated as piezoelectric devices for various applications. Notably, the piezoelectric performance of PVDF-based platforms is determined by their structural characteristics at different scales. This Review highlights how researchers can strategically engineer structures on microscopic, mesoscopic, and macroscopic scales. We discuss advanced research on PVDF-based piezoelectric platforms with diverse structural designs in biomedical sensing, disease diagnosis, and treatment. Ultimately, we try to give perspectives for future development trends of PVDF-based piezoelectric platforms in biomedicine, providing valuable insights for further research.

Preparation of Semiconducting Films By Electrooxidation of Naphthalene

Due to promising electronic and optical properties, conductive polymers are attracting significant interest. Conductive polymers find applications in electronic devices, e.g. substituted polynaphthalenes are used as blue light sources in OLEDs1. The ability to block the substitution sites where the subsequent polymer unit may be added by functional groups allows the polymer structure to be designed2. Moreover, one of the benefits of conductive polymers is the ability to modify the band gap of these materials by adding substituents to the main chain.Naphthalene, as the smallest polycyclic hydrocarbon, is an interesting precursor for synthesis semiconducting materials. The anodic oxidation of naphthalene has been described several times in the literature3,4, however, only formation of 1,4-polynaphthalene in the form of a granular product has been reported.In our research, we performed naphthalene electrooxidation and investigated the impact of the experimental conditions such as naphthalene concentration, water content, and electrode material on the obtained semiconducting materials. We used mass spectrometry to observe mass progression and determine molecular mass of the obtained polymers. The results of electron microscopy imaging showed fine quality coating. We studied the electronic properties of the polymers by cyclic voltammetry and impedance spectroscopy. Based on the results, we discussed the possible mechanism of the reaction. Samanta, S. K. et al. Synthesis of high molecular weight 1,4-polynaphthalene for solution-processed true color blue light emitting diode. Macromolecules 51, 8324–8329 (2018).Debad, J. F. & Bard, A. J. Electropolymerization of acenaphtho[1,2-k]fluoranthene derivatives: Formation of a new conductive electroactive electrochromic hydrocarbon ladder polymer. J Am Chem Soc 120, 2476–2477 (1998).Zecchin, S., Tomat, R., Schiavon, G. & Zotti, G. Polynaphthylene films from anodic coupling of naphthalene. Synthetic Metals vol. 25 (1988).Huang, Z., Qu, L., Shi, G., Chen, F. & Hong, X. Electrochemical polymerization of naphthalene in the electrolyte of boron trifluoride diethyl etherate containing trifluoroacetic acid and polyethylene glycol oligomer. Journal of Electroanalytical Chemistry 556, 159–165 (2003).

Bending Dielectric Elastomer Actuators

Dielectric Elastomer Actuators (DEAs) are a type of electroactive polymers that transform electric energy into mechanical work and are capable of large strains and high energy densities. DEAs are often described as “artificial muscles” because they exhibit strains, energy density, and responsiveness similar to natural human muscles. Their applications as soft robotic grippers, artificial arms, underwater robots, and aerial robots have previously been demonstrated. Single-layer DEAs have a simple design, with a dielectric layer sandwiched between compliant electrodes. However, by alternating positive and negative electrodes, multilayer DEAs can exhibit larger forces and strains than single-layer DEAs. DEAs are actuated by applying voltage and forming an electric field, generating a Maxwell stress between the electrodes. The process of fabricating a multilayer DEA consists of spin coating and curing layers of elastomer, stamping carbon nanotubes (CNT), and making connections to the electrodes. By alternating positive and negative electrodes, multilayer DEAs are constructed, which can exhibit larger forces and strains than single-layer DEAs. When electrically activated, DEAs expand laterally; however, by fabricating a bimorph DEA actuator, we demonstrate bending DEAs. A bimorph DEA consists of a multilayer DEA layer attached to a thicker inactive elastomer layer. When the bimorph is actuated, only the DEA layer expands, causing the actuator to bend. We study the relationship between the bending and stiffness of the inactive layer. By changing the shape of the DEA to a triangle or wing-like shape, we also emulate the high-frequency flapping of birds. Work begun on characterizing the voltage-controlled deflection of bimorph DEAs and understanding the mechanics of the bending of a simple beam in terms of forces at Harvard University will be continued on the Navajo Reservation at Navajo Technical University.

Investigating Ion-Coupled Electron Transfer of Conducting Polymers

After years of basic and applied studies of electron transfer in redox active films, the fundamentals of ion transfer during the exchange remain to be understood. Empirically, the processes are ion-transport limited. Using a conducting polymer as a model system, we aim to study the relationship between electron and ion transfer during redox switching.We work on electrochromic conducting polymers because of their observable and detectable color changes in addition to the current during the redox switching. Tracing optical signals can enhance the understanding of electrical signals from redox reactions. When a potential is applied to the electroactive polymer, its color will change from lighter to darker or vice versa. Keeping in mind that absorbances are additive, the ratio of the contents that make up the overall color of the polymer changes. This ratio change is directly proportional to the amount of matter under inter-conversion during the redox reaction.This study aims to explore the ion-electron mechanism in conductive polymers using the simultaneous Spectro-CV method. To achieve this, we conducted cyclic voltammetry at exceptionally high scanning rates, leveraging the conductive polymer's color-changing property. At these high rates, ion movement was restricted due to limited time for forward and backward motion, potentially reaching a point of stagnation. The investigation focused on whether the polymer would continue changing color, providing insights into ion-electron transfer. In addition, we are conducting EIS measurements alongside simultaneous Spectro-CV measurements and attempting to fit the impedance response of the polymer with an appropriate model. We aim to track the time constants provided by the polymer at different voltage values and understand the corresponding physical processes associated with these time constants. Additionally, we aim to use our EIS model to validate the desired redox current information obtained from optical data. We mathematically reach the faradaic portion of the total current with EIS and compare the results obtained from optical data.

Electrogeneration and Characterization of Poly(methylene blue) Thin Films on Stainless Steel 316 Electrodes-Effect of pH.

Methylene blue was electropolymerized on the surface of stainless steel 316. The addition of sodium oxalate and working at a pH near 11 allowed us to obtain steel electrodes coated with an electroactive polymer. This polymer shows electrochromic properties like those of the monomer, but also exhibits electroactivity at more positive potentials, which is associated with the active centers in the bridges between monomeric units. A digital video electrochemistry study allowed us to simultaneously quantify, on the one hand, the color changes on the entire surface of the stainless steel and on the other to separate the contribution of the active centers of the phenothiazine ring and of the inter-monomer bonds to the overall polymer response by means of assessing the mean color intensities. A reduction mechanism for the polymer, compatible with the pH variation of the observed electrochemical behavior, was proposed.

Improving interactions at the electrochromic polymer‐transparent oxide electrode interface using alkyl phosphonic acid modifiers

AbstractAs new synthetic methods for the preparation of solution processable electrochromic polymers are explored, including increasing synthetic scale beyond that of the research laboratory, it is expected that polymer intermolecular and intramolecular interactions will be affected. In this study, we explore the use of four different alkyl phosphonic acids of differing chain lengths as an interfacial treatment on ITO transparent electrodes to improve the polymer‐electrode interactions to mitigate the loss of film integrity and resulting electrochromic properties (current density, optical properties, and effective switch rates) during repeated oxidation/reduction and swelling/deswelling of the film. It was found that the phosphonic acid layer allows for a compatibilization of the polarity of the electrode surface with the polymer layer while also improving surface energy uniformity. We evaluated two electrochromic polymers (ECPs), and while a near complete delamination was observed on untreated ITO, film integrity was maintained beyond 25 repeated cycles, with polymer optical contrast maintained at all switching rates when coated onto dodecylphosphonic acid. Additionally, we show that electrochromic polymer film integrity is maintained over a range of film thicknesses. This method can be extended to applications using a variety of solution processable electroactive polymers in contact with metal oxide surfaces.

Tear Fracture Analysis of Fiber-Reinforced Conducting Polymer-based Soft Actuator

Conducting polymer (CP) is an electroactive polymer that displays specific electronic properties, including conductivity. The utility of CP-based soft actuators in various biomedical applications has recently been motivated due to their low voltage-driven specialty compared to the widely used high voltage-driven dielectric elastomers. In some biomedical applications, highly delicate CP actuators may be torn or damaged for unknown reasons. In this regard, this study develops a tear fracture model for fiber-reinforced CP actuators to investigate a specific fracture test of mode III, namely, the trousers test, which involves pulling two legs of a cut specimen horizontally apart. The development of the tear fracture model adopts a well-known Griffith criterion along with the thermodynamically consistent continuum mechanics approach. Additionally, prominent strain energy capturing elastomer strain-stiffening at a moderate strain range is used in conjunction with an empirically established correlation to couple the two internal phenomena, ion diffusion and mechanical deformation of the CP actuators. Later, the effects of various electrical and geometrical parameters on the tearing of the actuator are also addressed.

A Straightforward Approach of Wet‐Spinning Poly(3,4‐ethylenedioxythiophene):Polystyrene Sulfate Fibers for Use in All Conducting Polymer‐Based Textile Actuators

Poly(3,4‐ethylenedioxythiophene) (PEDOT), an inherently electrically conductive or conjugated polymer (CP), exhibits the potential to play a significant role in the development of innovative fiber materials for use in smart textiles, such as wearables. Furthermore, these fibers can function as artificial muscles in the emerging field of interactive fiber rubber composites. This study introduces a straightforward and efficient method for creating PEDOT‐based, biomimetic, fiber‐shaped, linearly contracting ionic electroactive polymer actuators. To achieve this, a wet‐spinning technique is presented, which enables a continuous production of PEDOT:polystyrene sulfate (PSS) fibers at high production rates of 34 m h−1, an additional fiber washing step and a sulfuric acid posttreatment step to increase the fibers conductivity. The fibers provide a high conductivity of 1028 S cm−1, maximum tensile strength reaching 182 MPa, and a maximum elongation of 24%. When utilized as CP actuators in an aqueous sodium dodecylbenzenesulfonate electrolyte medium, the fibers demonstrate a repeatable maximum isometric contractile force of 1.64 mN and repeatable linear contractile strain up to 0.56%. Furthermore, a high level of cyclic long‐term actuation stability can be demonstrated. Notably, these contractile strains are, to the best of knowledge, the highest reported values for pristine PEDOT:PSS fibers.

Enhancing antibacterial efficacy through propolis-infused electroactive polymers: A novel approach to combat antibiotic resistance

The increasing prevalence of antibiotic-resistant illnesses worldwide calls for the development of novel antibacterial strategies, including the ones based on antibacterials materials. This work reports on the combined antibacterial effects of piezoelectric poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) and propolis, a natural antimicrobial agent, on various material structures (2D films and 3D structures) to increase the surface contact area. It is shown that the addition of propolis has a substantial impact on the surface texture and mechanical properties of the materials. In particular, 3D structures exhibit improved distribution of propolis and enhanced mechanical stability in comparison to 2D films. The antibacterial experiments conducted on Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) demonstrate a significant increase in the reduction of bacteria, in particular when larger concentrations of propolis are applied and when mechanical stimulation is used at specified frequencies, taking therefore advantage of the surface charge variation associated to the piezoelectric response. It is particularly significant the antibacterial effect on the resistant S.aureus bacteria, emphasising the huge potential of this novel hybrid material in biomedical applications. Thus, it is demonstrated that piezoelectric polymers in combination with natural antibacterial agents, represents a suitable approach to address microbial resistance, with important applications in areas including wound dressings, implant coatings, and high traffic surfaces, among others.

Subsurface Profiling of Ion Migration and Swelling in Conducting Polymer Actuators with Modulated Electrochemical Atomic Force Microscopy.

Understanding the dynamics of ion migration and volume change is crucial to studying the functionality and long-term stability of soft polymeric materials operating at liquid interfaces, but the subsurface characterization of swelling processes in these systems remains elusive. In this work, we address the issue using modulated electrochemical atomic force microscopy as a depth-sensitive technique to study electroswelling effects in the high-performance actuator material polypyrrole doped with dodecylbenzenesulfonate (Ppy:DBS). We perform multidimensional measurements combining local electroswelling and electrochemical impedance spectroscopies on microstructured Ppy:DBS actuators. We interpret charge accumulation in the polymeric matrix with a quantitative model, giving access to both the spatiotemporal dynamics of ion migration and the distribution of electroswelling in the electroactive polymer layer. The findings demonstrate a nonuniform distribution of the effective ionic volume in the Ppy:DBS layer depending on the film morphology and redox state. Our findings indicate that the highly efficient actuation performance of Ppy:DBS is caused by rearrangements of the polymer microstructure induced by charge accumulation in the soft polymeric matrix, increasing the effective ionic volume in the bulk of the electroactive film for up to two times the value measured in free water.

Fractal Circuit Architectures for Spatially Controlled Heating and Multi-Modal Shape Programming of Electro-Active Shape Memory Polymers

Shape memory polymers (SMPs) are commonly activated through external heating or rigid embedded heaters, which lack precise temperature control and restrict programmable shape transformations. This study demonstrates integrating thin films of hard electronic materials patterned in fractal designs into SMPs yields novel thermomechanical responses, enabling flexible implementation of stretchable electronic functionality. Space-filling Hilbert, Moore and Peano fractal curves generate distributed electronic circuitry patterns within the SMP matrices. To investigate the coupled electro-thermal-mechanical behavior, a multi-physics modeling approach is adopted. A nonlinear thermo-visco-hyperelastic constitutive model captures the SMP’s shape memory characteristics. Governing equations for the multi-physics problem are formulated. Experimental data validates the model’s predictions of the SMP’s nonlinear material response under uniaxial loading. This validated framework analyzes SMP composites with integrated fractal circuits. Findings reveal composites with higher-order fractal circuits’ exhibit faster, more uniform resistive heating and smaller electrical resistance changes during stretching, enabling consistent and predictable shape recovery under various deformations. Notably, these advantageous heating and resistance characteristics enhance the force recovery rate during the shape memory cycle. Furthermore, the composites demonstrate excellent shape recovery under bending. Remarkably, uniaxial stretching can induce controlled out-of-plane shape transformations, enabling novel actuation modalities. This work provides insights into leveraging fractal circuit integration to enhance SMP performance and expand capabilities, enabling multi-functional actuators, sensors and programmable soft grippers.

The surface charge of electroactive materials governs cell behaviour through its effect on protein deposition

The precise mechanisms underlying the cellular response to static electric cues remain unclear, limiting the design and development of biomaterials that utilize this parameter to enhance specific biological behaviours. To gather information on this matter we have explored the interaction of collagen type-I, the most abundant mammalian extracellular protein, with poly(vinylidene fluoride) (PVDF), an electroactive polymer with great potential for tissue engineering applications. Our results reveal significant differences in collagen affinity, conformation, and interaction strength depending on the electric charge of the PVDF surface, which subsequently affects the behaviour of mesenchymal stem cells seeded on them. These findings highlight the importance of surface charge in the establishment of the material–protein interface and ultimately in the biological response to the material. Statement of significanceThe development of new tissue engineering strategies relies heavily on the understanding of how biomaterials interact with biological tissues. Although several factors drive this process and their driving principles have been identified, the relevance and mechanism by which the surface potential influences cell behaviour is still unknown. In our study, we investigate the interaction between collagen, the most abundant component of the extracellular matrix, and poly(vinylidene fluoride) with varying surface charges. Our findings reveal substantial variations in the binding forces, structure and adhesion of collagen on the different surfaces, which collectively explain the differential cellular responses. By exposing these differences, our research fills a critical knowledge gap and paves the way for innovations in material design for advanced tissue regeneration strategies.

Mathematical Analysis of Nonlinear Differential Equations in Polymer Coated Microelectrodes

A theoretical analysis is conducted on the electrochemical behaviour of micro disk electrodes coated with thin coatings of electroactive polymers. The main focus of efforts to characterize the planar diffusion chemical reaction within polymer-modified ultra-microelectrodes is the creation of a theoretical model that explicitly takes into account the potential for the polymer film to cover the inlaid micro disc support surface. Approximate formulae for the steady-state amperometric response and formulation of the boundary value problem are given. The impact of substrate concentration, mediator concentration and current responsiveness in the solution besides the polymer film is also investigated. Akbari-Ganji method (AGM) and differential transformation method (DTM), two adequate and widely available analytical methods, were utilized to determine the steady-state non-linear diffusion equation. The approximate analytical solution for the substrate concentration and mediator concentration and the current for the small experimental kinetic values and diffusion coefficients are presented. We additionally determine the problem’s numerical solution using the MATLAB tool. A satisfactory agreement can be seen when the numerical outcomes verify with the analytical findings.

Programmable DNA Nanomachine Integrated with Electrochemically Controlled Atom Transfer Radical Polymerization for Antibody Detection at Picomolar Level.

The quantitative detection of antibodies is crucial for the diagnosis of infectious and autoimmune diseases, while the traditional methods experience high background signal noise and restricted signal gain. In this work, we have developed a highly efficient electrochemical biosensor by constructing a programmable DNA nanomachine integrated with electrochemically controlled atom transfer radical polymerization (eATRP). The sensor works by binding the target antidigoxin antibody (anti-Dig) to the epitope of the recognization probe, which then initiates the cascaded strand displacement reaction on a magnetic bead, leading to the capture of cupric oxide (CuO) nanoparticles through magnetic separation. After CuO was dissolved, the eATRP initiators were attached to the electrode based on the CuΙ-catalyzed azide-alkyne cycloaddition. The subsequent eATRP reaction results in the formation of long electroactive polymers (poly-FcMMA), producing an amplified current response for sensitive detection of anti-Dig. This method achieved a detection limit at clinically relevant picomolar concentration in human serum, offering a sensitive, convenient, and cost-effective tool for detecting various biomarkers in a wide range of applications.

Electroactive Ionic Polymer of Intrinsic Microporosity for High-Performance Capacitive Energy Storage.

Here, an ionic polymer of intrinsic microporosity (PIM) as a high-functioning supercapacitor electrode without the need for conductive additives or binders is reported. The performance of this material is directly related to its large accessible surface area. By comparing electrochemical performance between a porous viologen PIM and a nonporous viologen polymer, it is revealed that the high energy and power density are both due to the ability of ions to rapidly access the ionic PIM. In 0.1m H2SO4 electrolyte, a pseudocapacitve energy of 315 F g-1 is observed, whereas in 0.1m Na2SO4, a capacitive energy density of 250 F g-1 is obtained. In both cases, this capacity is retained over 10000 charge-discharge cycles, without the need for stabilizing binders or conductive additives even at moderate loadings (5mg cm-2). This desirable performance is maintained in a prototype symmetric two-electrode capacitor device, which has >99% Coloumbic efficiency and a <10 mF capacity drop over 2000 cycles. These results demonstrate that ionic PIMs function well as standalone supercapacitor electrodes and suggest ionic PIMs may perform well in other electrochemical devices such as sensors, ion-separation membranes, or displays.

Efficient large-deformation shell elements for the simulation of electromechanical coupling effects in incompressible dielectric elastomers

So-called electro-active polymers are not only capable of undergoing very large deformations, but they also exhibit different electromechanical coupling effects due to their dielectric or electrostrictive characteristics. In the present paper the sub-class of dielectric elastomers is studied; in particular, we focus on thin dielectric elastomer shells, which undergo large deformations under an applied electric field. We develop a framework for the modeling and subsequent efficient simulation of thin structures made from incompressible dielectric elastomers. A thermodynamically consistent phenomenological continuum model based on the free energy density is adapted imposing the kinematic assumptions of Kirchhoff-Love shells in combination with including the thickness deformation and the electric field as independent unknown fields. To make the formulation accessible to finite element simulations, existing non-linear elastic shell mixed finite elements are extended to the present hyperelastic electromechanically coupled formulation for dielectric elastomer shells. Computational results of the shell theory are compared to three-dimensional results validating the proposed modeling and numerical simulation methodology, and showing high accuracy already for coarse finite element discretizations of the shell.