Electrochemomechanical Deformation Research Articles

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).

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.

Role of polymerization temperature on the performance of polypyrrole/dodecylbenzenesulphonate linear actuators

Polypyrrole doped with dodecylbenzenesulphonate (PPy/DBS) free-standing films were electropolymerized in sodium perchlorate propylene carbonate solution at different temperatures, observing increasing conductivity with decreasing synthesis temperature. Our goal in this study was to evaluate how the linear actuation of PPy depends on the polymerization temperature. The anion driven actuation of materials synthesized at lower temperatures changed to mainly cation active for PPy/DBS films polymerized at 20 °C; the latter films also showed the highest diffusion coefficients. Scanning electron microscopy did show that the surface roughness of the films increased with increasing synthesis temperature, as expected. Isometric and isotonic electro-chemo mechanical deformation (ECMD) measurements were performed with combined electrochemical techniques (cyclic voltammetry and chronoamperometry), revealing wide differences in the actuation behavior.

Poly(ethylene oxide) in polypyrrole doped dodecylbenzenesulfonate: characterisation and linear actuation

We show improvement in linear actuation properties of polypyrrole-doped dodecylbenzenesulfonate (PPy/DBS) by incorporating varying amounts of polyethylene oxide (5 wt % or 15 wt %) into PPy during electroploymerisation (PPy/DBS-PEO). Knowing that pristine PPy/DBS linear actuators in aqueous electrolytes are driven by cation ingress during reduction, the actuation properties are studied in isotonic (length change) mode of electro-chemo-mechanical-deformation (ECMD) measurements. Scanning electronic microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy revealed that PEO is incorporated in PPy/DBS films. ECMD studies revealed a three-fold improvement in electronic conductivity for the PPyDBS-PEO 15% film that also demonstrated improved strain of 7% in comparison to the strain of PPy/DBS film of 1.9%.

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.

Recent Advances on Polypyrrole Electroactuators.

Featuring controllable electrochemomechanical deformation and excellent biocompatibility, polypyrrole electroactuators used as artificial muscles play a vital role in the design of biomimetic robots and biomedical devices. In the past decade, tremendous efforts have been devoted to their optimization on electroactivity, electrochemical stability, and actuation speed, thereby gradually filling the gaps between desired capabilities and practical performances. This review summarizes recent advances on polypyrrole electroactuators, with particular emphases on novel counterions and conformation-reinforcing skeletons. Progress and challenges are comparatively demonstrated and critically analyzed, to enlighten future developments of advanced electroactuators based on polypyrrole and other conducting polymers.

Enhancement of polypyrrole linear actuation with poly(ethylene oxide)

In the present paper, we report the electro-chemo-mechanical deformation (ECMD) measurements of pristine polypyrrole (PPy) and polypyrrole/poly(ethylene oxide) composite films doped with dodecylbenzenesulfonate (DBS) under isotonic (constant force) conditions. The PPy/DBS and PPy-PEO/DBS films, the latter made from a polymerization solution containing 5wt% PEO, were actuated potentiodynamically in an aqueous solution containing lithium bis-trifluoromethane-sulfonimide (LiTFSI). The obtained composite films were characterized with scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy and Fourier transform infrared spectroscopy (FTIR). The results confirmed the successful incorporation of PEO within the PPy film. The composite films showed a remarkable improvement in maximum strain achieved (of 7.7%), nearly double that of the pristine PPy/DBS film, had a higher conductivity, higher ion diffusion coefficient and faster strain rate. The ECMD measurements for both the pristine as well as the PEO-composite films showed cation driven actuation involving the migration of Li+ cations in the aqueous electrolyte.

Inkjet‐printed hybrid conducting polymer-activated carbon aerogel linear actuators driven in an organic electrolyte

A novel trilayer ionic electro-chemo-mechanical actuator consisting of a 5-μm thick hybrid conducting polymer (CP) poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) and nanoporous activated carbon aerogel (ACA) electrodes printed on a commercial poly(vinylidene fluoride) (PVdF) membrane is reported. Recent studies have introduced hybrid CP-carbon bending and expanding actuators with the aim of enhancing the capacitive properties and energy efficiency of the actuator. The current study is focused on characterizing the ion‐transport properties of the material and determining the effect of nanoporous carbon in hybrid actuators. To analyze the ion diffusion and electro-chemo-mechanical properties of the trilayer, electro-chemo-mechanical deformation (ECMD) measurements were conducted in linear actuation mode, connecting both sides of the trilayer as the working electrode in an electrolyte setup. While the PEDOT:PSS trilayer shows nearly double the strain of the PEDOT:PSS-ACA trilayer, the stress is higher in the case of PEDOT:PSS-ACA. Despite the decreased strain [1], ACA incorporation in PEDOT:PSS results in faster ion transport and also adds anion migration to the otherwise cation‐active actuation of PEDOT:PSS. This work shows, for the first time, the potential of inkjet print fabrication of CP-carbon aerogel hybrid actuators.

Electrolyte and solvent effects in PPy/DBS linear actuators

An important question with conducting polymer linear actuators concerns the processes that occur once the electrolyte is changed. To address this question, a series of electro-chemo-mechanical deformation (ECMD) measurements on electrochemically prepared free-standing films of polypyrrole doped with dodecylbenzenesulfonate (DBS) were investigated under isometric (constant force) conditions in an organic solvent- and in aqueous based-electrolytes during cyclic voltammetric and square wave potential step experiments. The same film was actuated first in propylene carbonate electrolyte (0.1M TBACF3SO3), where cation-driven actuation (12% strain) was observed. The film was then exposed to an aqueous electrolyte (0.2M TMACl) where the actuation changed to anion-driven (7% strain). The same film was then returned to the propylene carbonate electrolyte, where anion-driven actuation (10% strain) was observed rather than the original cation-driven actuation. Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and scanning ionic conductance microscopy were applied to evaluate changes in morphology and electrochemical properties before and after the actuation cycles to examine changes in the actuation mode. The mechanism and reasons for the observed behaviour are proposed.

Electrochemistry of interlayer supported polypyrrole tri-layer linear actuators

Electro–chemo–mechanical deformation of polypyrrole doped with dodecylbenzenesulfonate (PPy/DBS), deposited electrochemically on chitosan and polyvinylidene fluoride (PVdF) substrates made conductive by chemically deposited poly(3,4-ethylenedioxythiophene) (PEDOT) are examined. The electronic conductivity and structural properties (by Raman and FTIR spectroscopy) of the chemically deposited PEDOT on chitosan film and PVdF membrane are characterized. The linear actuation response of PPy/DBS films on the two substrates in tetrabutylammonium trifluoromethanesulfonate in propylene carbonate electrolyte is investigated under isotonic (constant force) conditions. The goal of this study was to obtain novel linear actuators with mechanically stable tri-layer design and controllable strain, and to compare the effect of two completely different substrate materials on the properties of the conducting polymer coatings.

Stability of polypyrrole soft actuators in ionic liquids

Characteristics of electrochemomechanical deformation (ECMD) of polypyrrole films using ionic liquids are reported. The PPy film prepared by electrodeposition in an ionic liquid (1-Butyl-1-methylpyrrolidinium bis(trifluorometylsulfonyl)imide, BMPTFSI) was compact and high density. The other film prepared from LiTSFI/methyl benzoate and dimethyl phthalate mixed solvents was porous and low density. Both films demonstrated a stable ECMD in the ionic liquid. The strain of ECMD was 3-5% and superimposed on a creeping, showing a typical behaviour of cation movement. The Strains of ECMD in both films operated in a mixed electrolyte of BMPTFSI and propylene carbonate were enhanced up to 17- 25 %, showing anion movement. However, the large strain decreased upon several electrochemical cycles. The results were discussed in terms of swelling of the PPy film by solvents and loss of electrochemical activity.

Training and shape retention in conducting polymer artificial muscles

Electrochemomechanical deformation (ECMD) of the conducting polymer polyaniline filmis studied to investigate the behaviour of actuation under tensile loads. The ECMD wasinduced by the strains due to the insertion of ionic species (cyclic strain) and a creep due toapplied loads during the redox cycle. The cyclic strain was enhanced by the experience ofhigh tensile loads, indicating a training effect. The training effect was explained by theenhanced electrochemical activity of the film. The creep was recovered by removal of thetensile load and several electrochemical cycles. This fact indicates that the creep resultsfrom the one-dimensional anisotropic deformation, and is retained (shape retention) by theionic crosslink. The recovery of creep results from the elastic relaxation of the polymerconformation.

Shape Retention in Polyaniline Artificial Muscles

Behaviors of polyaniline artificial muscle under high tensile loads have been studied. The artificial muscle based on the electrochemomechanical deformation exhibits a large creep under high tensile loads. However, the creep is recovered by the removal of tensile loads and several electrochemical cycles. The facts indicate that the creep is due to the one dimensional anisotropic deformation. The anisotropic deformation is retained by the ionic crosslink at the oxidized state, and released by the cycling under load free.

Effect of polymerization potential on the actuation of free standing poly-3,4-ethylenedioxythiophene films in a propylene carbonate electrolyte

The linear actuation of poly-3,4-ethylenedioxythiophene (PEDOT) films polymerized at different potentials (0.8–1.3 V) at −27 °C in propylene carbonate (PC) solutions of TBACF3SO3 (tetrabutylammonium trifluoromethanesulfonate) was examined under isotonic (constant force) and isometric (constant length) conditions. The actuation properties were evaluated by electrochemomechanical deformation measurements (ECDM) during cyclic voltammetry, square wave potential steps and long term cycling. The ECDM response revealed mixed ion actuation behaviour for PEDOT films polymerized at the potential extremes of 0.8 and 1.3 V. At intermediate polymerization potentials from 0.9 to 1.2 V, cation-driven actuation was observed involving immobilized triflate anions (CF3SO3−). Long term experiments (50 cycles) showed that films prepared at polymerization potentials of 0.8 V exhibited mainly anion-driven actuation, during potential steps to and from 1.0 V; conversely PEDOT prepared at a polymerization potential of 1.1 V showed exclusively cation-driven actuation. PEDOT films prepared at a polymerization potential of 1.1 V showed the maximum cation-driven actuation during cyclic voltammetry experiments including long term cycling. SEM images showed an open porous structure in all of the PEDOT films.

Suppression of pH effect on the electrochemical deformation in polyaniline film

pH effect on the electrochemical deformation of freestanding polyaniline (PANi) film was investigated by means of electrochemomechanical deformation (ECMD) measurement. The maximum anodic expansion was found in PANi at around pH = 1.5 in aqueous acid consisted of HCl and NaCl. The deformation vs. redox charge ( D−Q) plots revealed the critical differences in the deformation characteristics below and above pH = 1.5. The similar pH dependences were also observed in other acidic media. Against these results, we investigated the surface coating effect of PANi film on deformation behaviors. It was revealed that the PPy coating on PANi film successfully reduced the pH dependence of the PANi/PPy film deformation. The results indicate that the buffer layer coated on the PANi film surface decreases the ion concentration effects on the PANi deformation. The result indicates the extensive usage of PANi actuator in wide pH aqueous media.

The actuation behavior and stability of p‐toluene sulfonate doped polypyrrole films formed at different deposition current densities

AbstractFree‐standing films of polypyrrole doped with p‐toluene sulfonate (PPy/pTS) were electropolymerized galvanostatically at different deposition current densities and their electrochemomechanical deformation (ECMD) properties were measured in situ during cyclic voltammetry experiments. It was found that films exhibiting a higher cation‐driven actuation strain were generated when a lower current density was used in electropolymerization, which also led to an increase in PPy conductivity and doping level. A decrease in cation‐driven strain with time was observed in all cases due to a loss of pTS anions from the films. Raman, FTIR, and elemental analyses were used to characterize the films grown at different deposition current densities and no sign of excessive overoxidation was found. SEM images revealed that the morphology of the films was affected by the current density during electropolymerization. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

The effect of monomer and electrolyte concentrations during synthesis on the actuation of PPy(CF 3SO 3) films in aqueous electrolytes

Free-standing films of polypyrrole, PPy(CF 3SO 3), were electropolymerised galvanostatically from propylene carbonate solutions containing tetrabutylammonium trifluoromethanesulfonate of a range of pyrrole or electrolyte concentrations. The electrochemomechanical deformation (ECMD), measured in situ during cyclic voltammetry experiments, was found to increase when a higher concentration of pyrrole monomer or CF 3SO 3 electrolyte was used during the polymerisation. X-ray photoelectron spectroscopy was used to estimate the presence of different forms of carbon in the PPy(CF 3SO 3) films, including the α and β carbons of the pyrrole ring, the ‘disordered carbon’ and carbonyl carbon. These XPS results were correlated with the strains observed in ECMD measurements and the doping level estimated from N1s XPS spectra. The morphology of the films obtained for different growth conditions was also investigated by means of SEM.

Effect of deposition current density on the linear actuation behaviour of PPy(CF3SO3) films

Abstract Free-standing films of PPy(CF 3 SO 3 ) were galvanostatically electropolymerised in propylene carbonate on a stainless steel electrode using different deposition current densities. The actuation performance of these films in an aqueous 1.0 M NaPF 6 electrolyte was investigated by in situ measurements of electrochemomechanical deformation (ECMD) during cyclic voltammetry experiments. The extent of linear strain of the films decreased with a higher deposition current density. X-ray photoelectron spectroscopy was used to estimate the amount of ‘disordered carbon’, carbonyl carbon and the doping level of the films. These values were related to the strain obtained from ECMD measurements. SEM images revealed a denser film morphology for films deposited using a lower current density.

Actuation of polypyrrole films in propylene carbonate electrolytes

The actuation properties of free standing PPy films polymerised from propylene carbonate (PC) solutions of tetrabutylammonium triflouromethanesulfonate (TBACF3SO3) and tetrabutylammonium hexaflourophosphate (TBAPF6) electrolytes were investigated by means of electrochemomechanical deformation (ECMD) measurements during cyclic voltammetry (CV) and chronoamperometry. The ECMD properties of the films were studied in PC/TBAPF6 and PC/TBACF3SO3 electrolytes to determine the effect of both the preparation and cycling electrolytes. Most systems showed mixed-ion actuation, although PPy/TBACF3SO3 films exhibited greater cathodic actuation. However, the extent of anodic actuation exceeded the cathodic actuation in all cases. When the cycling electrolyte was different from the preparation electrolyte it was found that the size of the anion at preparation had a critical effect: smaller PF6− anions in PPy/TBAPF6 films cannot be easily ion-exchanged for the larger CF3SO3−, which also had a tendency to stay entrapped in the polymer network, resulting in decreased anodic actuation and an increase in cathodic (cation-driven) actuation. On the contrary, significant cathodic movement for PPy/TBACF3SO3 films was suppressed when the cycling electrolyte was changed to PC/TBAPF6. Chronoamperometry was used to examine the kinetics of actuation in the positive potential region and electrochemical potential step experiments to investigate the long-term stability of the studied systems.

Conducting polymer soft actuators based on polypyrrole films—energy conversionefficiency

The electrochemomechanical deformation (ECMD) of conducting polymers can be usedto create soft actuators or transducers for the conversion of electric power tomechanical work. Polypyrrole (PPy) films, which were electrodeposited from amethyl benzoate solution of tetrabutylammonium (TBA) trifluoromethansulfonate,TBACF3SO3, were used to investigate the energy conversion efficiency. The films are known to havehigh tensile strength and to produce large strain at high stress in ECMD. The current asa function of load stress under constant applied potentials versus a referenceelectrode was studied in various electrolytes. Reduction currents increased withincreasing load stress for contraction of the film (lifting weights) as well as for theoxidation current (expansion), indicating that the electrical input was sensing theload hung on the actuators. During the contraction, the conversion efficiency wasestimated from the mechanical work energy. The maximum work energy-per-cycle was140 kJ m−3. It has been found that the energy conversion efficiencies are very small(<0.25%). Most of the input electrical energy is stored electrochemically, but a significant fraction isalso dissipated.