Exchanged cations and water during reactions in polypyrrole macroions from artificial muscles

Polypyrrole with Embedded Carbide-Derived Carbon with and without Phosphor Tungsten Acid: Linear Actuation and Energy Storage

Researchers have focused on incorporating porous carbon particles such as carbon-derived carbon (CDC) into polypyrrole (PPy), preferably on the surface, to achieve high-capacitive electrodes. Less attention is afforded to their linear actuation properties. Therefore, in this work, we chose two different electropolymerization processes using the typical PPy doped with dodecylbenzene sulfonate (DBS⁻) and added CDC particles, compared with CDC with phosphotungstic acid (PTA), forming CDC-PT⁴⁻ dopants. The resulting PPy/DBS-CDC (PPyCDC) and PPy/DBS-CDC-PT (PPyCDC-PT) films showed different morphologies, with PPyCDC having the most CDC particles on the surface with less surrounding PPy, while in PPyCDC-PT, all the CDC particles were covered with PPy. Their linear actuation properties, applying electrochemical techniques (cyclic voltammetry and square wave potential steps), were found to enhance the PPyCDC-PT films in organic (2-times-higher strain) and aqueous electrolytes (2.8-times-higher strain) in an applied potential range of 0.8 V to −0.5 V. The energy storage capability found for the PPyCDC was favorable, with 159 ± 13 F cm⁻³ (1.2 times lower for PPyCDC-PT) in the organic electrolyte, while in the aqueous electrolyte, a result of 135 ± 11 F cm⁻³ was determined (1.8 times lower for PPyCDC-PT). The results showed that PPyCDC was more favorable in terms of energy storage, while PPyCDC-PT was suitable for linear actuator applications. The characterization of both the film samples included scanning electron microscopy (SEM), Raman, FTIR, and energy-dispersive X-ray (EDX) spectroscopy.

Role of Polyoxometalate Contents in Polypyrrole: Linear Actuation and Energy Storage

A combination of polyoxometalates with polypyrrole is introduced in this work. Our goal was to include phosphotungstic acid (PTA) in different molar concentrations (0.005, 0.01, and 0.05 M) in the electropolymerization of pyrrole doped with dodecylbenzene sulfonate (DBS) and phosphotungstinates (PT), forming PPy/DBS-PT films. Scanning electron microscopy (SEM) revealed that the PPy/DBS-PT films became denser and more compact with increasing PTA concentrations. The incorporation of PT in PPy/DBS was analyzed using Fourier-transform infrared (FTIR) and energy dispersive X-ray (EDX) spectroscopy. The linear actuation in cyclic voltammetry and potential square wave steps in an organic electrolyte revealed increasing mixed actuation, with major expansion upon oxidation found for PPy/DBS-PT films with a PTA concentration of 0.005 M. Best results of a strain of 12.8% and stress at 0.68 MPa were obtained for PPy/DBS-PT (0.01 M). The PPy/DBS-PT films polymerized in the presence of 0.05 M of PTA and showed main expansion upon reduction, changing the actuation direction. Chronopotentiometric measurements of PPy/DBS-PT samples were conducted to determine the specific capacitance optimal for a 0.01 M PTA concentration in the range of 80 F g⁻¹ (±0.22 A g⁻¹).

Polypyrrole Polyethylene Composite for Controllable Linear Actuators in Different Organic Electrolytes

Controllable linear actuation of polypyrrole (PPy) is the envisaged goal where only one ion dominates direction (here anions) in reversible redox cycles. PPy with polyethylene oxide (PEO) doped with dodecylbenzenesulfonate forms PPy-PEO/DBS films (PPy-PEO), which are applied in propylene carbonate (PC) solvent with electrolytes such as 1-ethyl-2,3-dimethylimidazolium trifluoromethanesulfonate (EDMICF₃SO₃), sodium perchlorate (NaClO₄) and tetrabutylammonium hexafluorophosphate (TBAPF₆) and compared in their linear actuation properties with pristine PPy/DBS samples. PPy-PEO showed for all applied electrolytes that only expansion at oxidation appeared in cyclic voltammetric studies, while pristine PPy/DBS had mixed-ion actuation in all electrolytes. The electrolyte TBAPF₆-PC revealed for PPy-PEO best results with 18% strain (PPy/DBS had 8.5% strain), 2 times better strain rates, 1.8 times higher electronic conductivity, 1.4 times higher charge densities and 1.5 times higher diffusion coefficients in comparison to PPy/DBS. Long-term measurements up to 1000 cycles at 0.1 Hz revealed strain over 4% for PPy-PEO linear actuators, showing that combination of PPy/DBS with PEO gives excellent material for artificial muscle-like applications envisaged for smart textiles and soft robotics. FTIR and Raman spectroscopy confirmed PEO content in PPy. Electrochemical impedance spectroscopy (EIS) of PPy samples revealed 1.3 times higher ion conductivity of PPy-PEO films in PC solvent. Scanning electron microscopy (SEM) was used to investigate morphologies of PPy samples, and EDX spectroscopy was conducted to determine ion contents of oxidized/reduced films.

Polypyrrole with Phosphor Tungsten Acid and Carbide-Derived Carbon: Change of Solvent in Electropolymerization and Linear Actuation

Linear actuators based on polypyrrole (PPy) are envisaged to have only one ion that triggers the actuation direction, either at oxidation (anion-driven) or at reduction (cation-driven). PPy doped with dodecylbenzenesulfonate (PPy/DBS) is the most common applied conducting polymer having cation-driven actuation in aqueous solvent and mainly anion-driven actuation in an organic electrolyte. It is somehow desired to have an actuator that is independent of the applied solvent in the same actuation direction. In this research we made PPy/DBS with the addition of phosphorus tungsten acid, forming PPyPT films, as well with included carbide derived carbon (CDC) resulting in PPyCDC films. The solvent in electropolymerization was changed from an aqueous ethylene glycol mixture to pure EG forming PPyPT-EG and PPyCDC-EG composites. Our goal in this study was to investigate the linear actuation properties of PPy composites applying sodium perchlorate in aqueous (NaClO₄-aq) and propylene carbonate (NaClO₄-PC) electrolytes. Cyclic voltammetry and square potential steps in combination with electro-chemo-mechanical-deformation (ECMD) measurements of PPy composite films were performed. The PPyPT and PPyCDC had mixed ion-actuation in NaClO₄-PC while in NaClO4-aq expansion at reduction (cation-driven) was observed. Those novel PPy composites electropolymerized in EG solvent showed independently which solvent applied mainly expansion at reduction (cation-driven actuator). Chronopotentiometric measurements were performed on all composites, revealing excellent specific capacitance up to 190 F g^-1 for PPyCDC-EG (best capacitance retention of 90 % after 1000 cycles) and 130 F g^-1 for PPyPT-EG in aqueous electrolyte. The films were characterized by scanning electron microscopy (SEM), Raman, Fourier-transform infrared (FTIR) and energy dispersive X-ray spectroscopy (EDX).

Ion Mobility in Thick and Thin Poly-3,4 Ethylenedioxythiophene Films-From EQCM to Actuation

Conductive polymer actuators and sensors rely on controlled ion transport coupled to a potential/charge change. In order to understand and control such devices, it is of paramount importance to understand the factors that determine ion flux at various conditions, including the synthesis potential. In this work, the ion transport in thinner poly-3,4-ethylenedioxythiophene (PEDOT) films during charge/discharge driven by cyclic voltammetry is studied by consideration of the electrochemical quartz crystal microbalance (EQCM) and the results are compared to the actuation responses of thicker films that have been synthesized with the same conditions in the bending and linear expansion modes. The effects of polymerization potentials of 1.0 V, 1.2 V, and 1.5 V are studied to elucidate how polymerization potential contributes to actuation, as well the involvement of the EQCM. In this work, it is revealed that there is a shift from anion-dominated to mixed to cation-dominated activity with increased synthesis potential. Scanning electron microscopy shows a decrease in porosity for the PEDOT structure with increasing synthesis potential. EQCM analysis of processes taking place at various potentials allows the determination of appropriate potential windows for increased control over devices.

Antagonist Concepts of Polypyrrole Actuators: Bending Hybrid Actuator and Mirrored Trilayer Linear Actuator

Following the natural muscle antagonist actuation principle, different adaptations for "artificial muscles" are introduced in this work. Polypyrrole (PPy) films of different polymerization techniques (potentiostatic and galvanostatic) were analyzed and their established responses were combined in several ways, resulting in beneficial actuation modes. A consecutive "one-pot" electrosynthesis of two layers with the different deposition regimes resulted in an all-PPy bending hybrid actuator. While in most cases the mixed-ion activity of conductive polymers has been considered a problem or a drawback, here for the first time, the nearly equal expansions upon oxidation and reduction of carefully selected conditions further allowed to fabricate a "mirrored" trilayer laminate, which behaved as a linear actuator.

Probing the Electrolyte Transfer in Ultrathin Polypyrrole Films by In Situ X-ray Reflectivity and Electrochemistry

This study reports on the potential-induced charge and mass transfer between an ultrathin polypyrrole (PPy) film and an electrolyte by simultaneous in situ X-ray reflectivity (XRR) and electrochemistry (EC) utilizing their sensitivity to electrons. An about 30 nm thin PPy film was deposited on a silicon single crystal by fast potential cycling, providing a dense film of an extraordinary small surface roughness. XRR was recorded from the PPy film in an aqueous 0.1 M perchloric acid at electric potentials between -0.2 V and +0.5 V vs Ag/AgCl. The PPy film shows typical reversible and linear changes in film thickness and electron density arising from the potential-dependent electrolyte incorporation. By introducing EC-XRR, a comprehensive analysis combining in situ XRR and EC, the net number of electrons passing through the PPy-electrolyte interface was deduced along with the potential-induced thickness variations, indicating a complex exchange mechanism. Evidently, along with the anion transfer, parallel charge compensation by protons and a volume and electron compensating counterflow of solvent molecules take place. Complementary time-dependent EC-XRR scans indicate that these exchange mechanisms are individual in two potential ranges. The low actuation along with a high pseudocapacitance suggest the fast potentiodynamically deposited PPy film as a promising supercapacitor material.

Multifunctionality of Polypyrrole Polyethyleneoxide Composites: Concurrent Sensing, Actuation and Energy Storage

In films of conducting polymers, the electrochemical reaction(s) drive the simultaneous variation of different material properties (reaction multifunctionality). Here, we present a parallel study of actuation-sensing-energy storage triple functionality of polypyrrole (PPy) blends with dodecylbenzenesulfonate (DBS-), PPy/DBS, without and with inclusion of polyethyleneoxide, PPy-PEO/DBS. The characterization of the response of both materials in aqueous solutions of four different salts indicated that all of the actuating, sensing and charge storage responses were, independent of the electrolyte, present for both materials, but stronger for the PPy-PEO/DBS films: 1.4× higher strains, 1.3× higher specific charge densities, 2.5× higher specific capacitances and increased ion-sensitivity towards the studied counterions. For both materials, the reaction energy, the material potential and the strain variations adapt to and sense the electrical and chemical (exchanged cation) conditions. The driving and the response of actuation, sensing and charge can be controlled/read, simultaneously, via just two connecting wires. Only the cooperative actuation of chemical macromolecular motors from functional cells has such chemical multifunctionality.

Printed PEDOT:PSS Trilayer: Mechanism Evaluation and Application in Energy Storage

Combining ink-jet printing and one of the most stable electroactive materials, PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)), is envisaged to pave the way for the mass production of soft electroactive materials. Despite its being a well-known electroactive material, widespread application of PEDOT:PSS also requires good understanding of its response. However, agreement on the interpretation of the material's activities, notably regarding actuation, is not unanimous. Our goal in this work is to study the behavior of trilayers with PEDOT:PSS electrodes printed on either side of a semi-interpenetrated polymer network membrane in propylene carbonate solutions of three different electrolytes, and to compare their electroactive, actuation, and energy storage behavior. The balance of apparent faradaic and non-faradaic processes in each case is discussed. The results show that the primarily cation-dominated response of the trilayers in the three electrolytes is actually remarkably different, with some rather uncommon outcomes. The different balance of the apparent charging mechanisms makes it possible to clearly select one electrolyte for potential actuation and another for energy storage application scenarios.

Improving the Electrochemical Performance and Stability of Polypyrrole by Polymerizing Ionic Liquids

Polypyrrole (PPy) based electroactive materials are important building blocks for the development of flexible electronics, bio-sensors and actuator devices. As the properties and behavior of PPy depends strongly on the operating environment-electrolyte, solvent, etc., it is desirable to plant immobile ionic species into PPy films to ensure stable response. A premade ionic polymer is not optimal in many cases, as it enforces its own structure on the conducting polymer, therefore, polymerization during fabrication is preferred. Pyrrole (Py) was electropolymerized at low temperature together with a polymerizable ionic liquid (PIL) monomer in a one-step polymerization, to form a stable film on the working electrode. The structure and morphology of the PPyPIL films were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier-transform infrared (FTIR) spectroscopy and solid-state NMR (ssNMR) spectroscopy. The spectroscopy results confirmed the successful polymerization of Py to PPy and PIL monomer to PIL. The presence of (TFSI-) anions that balance the charge in PPyPIL was confirmed by EDX analysis. The electrical properties of PPyPIL in lithium bis(trifluoromethanesulfonyl)-imide (LiTFSI) aqueous and propylene carbonate solutions were examined with cyclic voltammetry (CV), chronoamperometry, and chronopotentiometry. The blend of PPyPIL had mixed electronic/ionic conductive properties that were strongly influenced by the solvent. In aqueous electrolyte, the electrical conductivity was 30 times lower and the diffusion coefficient 1.5 times higher than in the organic electrolyte. Importantly, the capacity, current density, and charge density were found to stay consistent, independent of the choice of solvent.

Electrochemomechanical Behavior of Polypyrrole-Coated Nanofiber Scaffolds in Cell Culture Medium

Glucose-gelatin nanofiber scaffolds were made conductive and electroactive by chemical (conductive fiber scaffolds, CFS) and additionally electrochemical polypyrrole deposition (doped with triflouromethanesulfonate CF3SO3-, CFS-PPyTF). Both materials were investigated in their linear actuation properties in cell culture medium (CCM), as they could be potential electro-mechanically activated cell growth substrates. Independent of the deposition conditions, both materials showed relatively stable cation-driven actuation in CCM, based on the flux of mainly Na+ ions from CCM. The surprising result was attributed to re-doping by sulfate anions in CCM, as also indicated by energy-dispersive X-ray (EDX) spectroscopy results. Overall, the electrochemically coated material outperformed the one with just chemical coating in conductivity, charge density and actuation response.

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.

Reactions driving conformational movements (molecular motors) in gels: conformational and structural chemical kinetics

E_a,k,αandβfrom reactions driving molecular polymeric motors constituting dense gels include quantitative conformational and structural information.

Mimicking muscle fiber structure and function through electromechanical actuation of electrospun silk fiber bundles

Fiber bundles composed of silk and conducting polymers undergo linear actuation, thus mimicking the structure and contractile function of muscles.

Asymmetric Bilayer Muscles: Cooperative Actuation, Dynamic Hysteresis, and Creeping in NaPF6 Aqueous Solutions

Three bilayer muscles [polypyrrole-paraphenolsulfonic acid/polypyrrole-dodecylbenzensulfonic acid (PPy-HpPS/PPy-DBS) asymmetric bilayer, PPy-HpPS/tape, and PPy-DBS/tape] were characterized during potential cycling in NaPF6 aqueous solutions. In parallel, the angular displacement of the muscle was video-recorded. The dynamo-voltammetric (angle-potential) and coulo-dynamic (charge-potential) results give the reaction-driven ionic exchanges in each PPy film. Electrochemical reactions drive the exchange of anions from the PPy-HpPS layer and cations from the PPy-DBS layer. This means that both layers from the asymmetric bilayer follow complementary volume changes (swelling/shrinking or shrinking/swelling), owing to complementary ionic exchanges (entrance/expulsion) driven by the bilayer oxidation or reduction. The result is a cooperative actuation; the bending amplitude described by the asymmetric bilayer muscle is one order of magnitude larger than those attained from each of the conducting polymer/tape muscles. The cooperative actuation almost eliminates creeping effects. A large dynamical hysteresis persists, which can be attributed to an irreversible reaction of the organic acid components at high overpotentials.

Electro-chemo-biomimetics from conducting polymers: fundamentals, materials, properties and devices

Conjugated conducting polymers, intrinsic conducting polymers or conducting polymers are complex and mixed materials; their electroactive fractions follow reversible oxidation/reduction reactions giving reversible volume variations to lodge or expel charge-balance counterions and osmotic-balance solvent molecules. The material content (reactive macromolecules, ions and water) mimics the dense intracellular matrix gel of living cells. Here the electropolymerization mechanism is reviewed highlighting the presence of parallel reactions resulting in electroactive and non-electroactive fractions of the final material. Conducting polymers are classified into nine different material families. Each of those families follows a prevalent reaction-driven exchange of anions or cations during oxidation/reduction (p-doping/p-dedoping or n-doping/n-dedoping). Polyaniline families also follow reaction-driven exchange of protons. The polymer/counterion composition changes for several orders of magnitude in a reversible way with the reversible reaction. The value of each of the different composition-dependent properties of the material also shifts in a reversible way driven by the reaction. Each property mimics another change in functional biological organs. A family of biomimetic devices is being developed based on each biomimetic property. Those electrochemical devices work driven by reactions of the constitutive material, as biological organs do. The simultaneous variation of several composition-dependent properties during the reaction announces an unparalleled technological world of multifunctional devices: several tools working simultaneously in one device. Such properties and devices are driven by electrochemical reactions: they are Faradaic devices and must be characterized by using electrochemical cells and electro-chemical methodologies.

Electrochemo-dynamical characterization of polypyrrole actuators coated on gold electrodes

Parallel reactions may have an important effect on conducting polymer actuation.

Carbide-derived carbon in polypyrrole changing the elastic modulus with a huge impact on actuation

With lowering of the elastic modulus, the CDC–POM–PPy composite shows a 20× improved strain response over PPy/DBS.

Electro-chemo-mechanical deformation properties of polypyrrole/dodecylbenzenesulfate linear actuators in aqueous and organic electrolyte

The immobilization of dodecylbenzenesulfonate (DBS⁻) in polypyrrole (PPy) during electropolymerization is typically expected to lead to cation-driven activity. Here we demonstrate that the actuation direction changed by using same electrolyte but different solvent.