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Herein, we demonstrate a method of intravascular catheter-based extrusion of hydrogels with in situ photomodulation to dynamically adjust the hydrogel properties utilizing a custom catheter setup. A novel UV-integrated microcatheter (luminal diameter 0.9 mm) was assembled and a suite of low-viscosity, shear thinning hydrogel precursors were formulated for delivery. We show that by modulating the precursor flow rate (up to 0.2 ml/min) as well as the UV power (0–37.5 mW), we can extrude hydrogels with viscosities dynamically varying from

Bioderived cellulose nanocrystals (CNCs) are used to create light, flexible, biocompatible, and biodegradable electronic devices. Herein, surface modification of cellulose nanocrystals was employed to fabricate cationic and anionic CNCs. Subsequently, we demonstrated rectification behavior from a fixed junction between two agarose hydrogels doped with cationic and anionic cellulose nanocrystals. The current rectification ratio reaches 70 reproducibly, which is significantly higher than that for analogous diodes generated with microfibrillated cellulose (∼15) and the first polyelectrolyte gel diode (∼40). The current-voltage characteristics of the CNC-hydrogel diode are influenced by concentration, gel thickness, scanning frequency, and applied voltage. The high surface area of CNC resulted in high charge density after surface modification, which in turn resulted in good rectification behavior from only small amounts of dopant material.

Flexible and stretchable capacitive pressure sensors have been developed in recent years due to their potential applications in health monitoring, robot skins, body activity measurements and so on. In order to enhance sensor sensitivity, researchers have changed structure of the dielectric of parallel plate capacitive sensor . Here we enhance the sensor sensitivities by changing electrode composition and explore the use of a woven electrode structure sensor with silver coated nylon yarn and EcoflexTM. The woven structure enhanced sensitivity 2.3 times relative to a simple cross-grid geometry (sensitivity was 0.003 kPa-1). Furthermore, it is also observed that the sensor with the woven electrode also had better repeatability and showed less creep than a device using carbon black electrodes. The woven structure of the electrodes enabled the device to be compliant, despite the presence of the stiff nylon fibres – thereby enabling good sensitivity without the creep seen in softer electrodes.

Electronically conducting polymer (ECP) actuators and sensors are ionic EAPs, whose working principle relies on the motion of ions, usually contained in an electrolyte, toward or from the electroactive polymer. We demonstrate here that linear deformation and sensing in open-air are accessible for ionic EAPs if classical trilayer devices are made electromechanically asymmetric by tuning the properties of PEDOT:PSS electrodes according to an electromechanical model. We also present the first results on “dry” ionic conducting membranes based on polymeric ionic liquids. This “dry” electrolyte allows developing ionic EAPs without any liquid component and still presenting large and fast bending deformation

Supercoiled polymer (SCP) actuators have shown promising applicability as artificial muscles due to their low-cost, high strains (10%+), work density that is more than 100 x that of muscle, and non-hysteretic behavior. Here, we present a lightweight, low-cost, SCP-actuated valve that operates by pinching rubber tubing closed. The valve comprises a 3D printable frame and incorporates a pulley system, which functions to reduce the total linear dimensions of the device. The actuator mechanism is compatible with different tubing diameters and materials and, by nature of its design, is isolated from direct contact with the working fluid. Using 1/4”/6.3 mm inside diameter latex tubing, a flow rate of up to 88 L/h and a holding pressure of over 29.4 kPa are demonstrated. The valve is normally open and takes 10 seconds to close by running a current through the coiled, silver-coated nylon actuator. An empirical model of the system is developed and open-loop control incorporated, which effectively reduced valve activation time by 30%. Further developments are suggested to achieve a faster response and pumping action.

International audience

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.

Electronic Conducting Polymers (ECP) have been widely studied in a tri-layer configuration as soft, bending actuators. These electroactive materials have also been reported to behave as mechanical strain sensors able to convert mechanical stimulation into electrical signals. This sensing behavior is attributed to the so-called piezoionic effect and is observed and reported in most ionic electroactive polymers (EAPs). However, ambiguities remain on the origin of this effect, being attributed either to stress gradient induced ion motion or to Donnan potentials arising at the ECP/electrolyte interface. In this work, the sensor mechanism of trilayer ECP actuators is studied and discussed as a function of different physical and chemical parameters thanks to the versatile synthesis of conducting interpenetrating polymer networks. Results demonstrate that the main mechanism relies on stress gradient, as in other ionic EAPs, instead of Donnan potential. Moreover, a deep investigation of the electrolyte nature and its concentration is performed. Mobile ions deduced from actuation experiments are correlated with the sign of voltage output during sensing experiments. An interesting inversion point is demonstrated at 2.5 M using 1-ethyl-3-methylimidazolium bis-(trifluoromethyl-sulfonyl)-imide electrolyte in propylene carbonate concentration where simultaneous charge compensation (no sensing) and volume compensation (no actuation) occur for mobile cations and anions, while electrochemical behaviour remains unchanged.

JIF=4.806; International audience; Low cost soft, flexible and stretchable sensors are being explored that can be applied to virtually any surface, and promise to enable tactile sensing on robots, prosthetics, skin and stretchable displays. Previous work has shown that capacitive sensors that are both stretchable and transparent can be created by using ionically conductive hydrogel electrodes. In this study, the electrodes are interpenetrating polymer networks swollen with ionic liquid, enabling high transparency and stretchability, without evaporation. The interpenetrating network is synthesized from poly(ethylene oxide) and nitrile butadiene rubber. Electrodes are patterned using femtosecond laser machining, creating stretchable electrodes. These were encapsulated in a polydimethylsiloxane substrate, producing a 95% transparent sensor (450 nm). A 4x4 tactile array shows the ability to sense proximity and multi-touch, as well as be robust to variations in environmental temperature (from 4 °C to 72 °C). Temperature change has a large effect on the resistance of the electrodes - an effect that could be used to measure device temperature. In addition, the sensor is able to detect proximity and touch while on skin, when covered by a layer of fabric or during stretch.

Metals and glass are excellent for containing electrolytes and liquids in general, but their rigid mechanics limits their application for mechanically active ionic actuators or flexible/ stretchable electrochemical devices such as batteries and supercapacitors. In this study, we evaluate the performance of spray-coated poly (styrene-block-isobutylene-block-styrene) (SIBS) as a stretchable encapsulant, which suggests that it offers a better combination of compliance and impermeability than any other barrier. We examined the drying time of 360-&micro, m thick encapsulated tri-layer conducting polymer (CP) actuators, comprised of poly(3,4-Ethylenedioxythiophene) (PEDOT) as the CP electrode and an interpenetrated polymer network of polyethylene oxide (PEO) and nitrile butadiene rubber (NBR) as the separator layer, which operates with a 1 M solution of Lithium bis(trifluoromethanesulfonyl)imide (Li+TFSI&minus, ) in propylene carbonate (PC). A 100-&micro, m thick SIBS encapsulation layer is anticipated to help these devices to retain 80% of stored PC for more than 1000 times longer compared to when there is no encapsulation (from less than 0.5 days to over 1.5 years). This low permeability combined with the low Young&rsquo, s modulus of the SIBS film, its biocompatibility, biostability, and FDA approval, as well as ease of fabrication, make this thermoplastic elastomer a promising candidate as an encapsulant for flexible ionic devices such as flexible batteries and supercapacitors, ionic-electrode capacitive sensors, and ionically electroactive actuators. This paves the way for using these devices in implantable and in vivo applications.

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 0.95 mm diameter device is shown to achieve a 22 mm radius of curvatures under activation of 2 V. 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.

JIF=3.543; International audience; Trilayer conducting polymer 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 conducting polymer actuators is proposed to predict their non-linear 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 non-linear 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.

An integrated solar energy conversion and storage system is presented using a dye sensitized electrode in a redox battery structure. A stable discharge voltage is shown with high areal energy storage capacity of 180 µW h cm−2 by choosing iodide/polysulfide as the pair of active materials matched with permeable porous electrodes. The solar rechargeable battery system offers a higher round-trip efficiency and potential cost savings on fabrication compared to individual devices.

A novel pressure sensor is proposed exhibiting generative properties from displacement-induced ionic charge separation in gel electrolytes. A mechano-ionic or ‘piezo-ionic’ effect, in analogy to the well-known piezoelectric effect, is hypothesized to originate from a difference in mobilities between cationic and anionic species causing a localized ionic charge gradient upon application of pressure. This gradient can be detected as a voltage or current by using copper electrodes placed at the sides or at regular intervals along a surface of the gel. The voltage generated may be a result of the local concentration gradient induced by the deformation of the gel or perhaps is the result of some ions moving faster through the porous gel than others. In this work, ionic polymer gels based on Poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) co-polymer were synthesized in situ to incorporate an organic electrolyte consisting of bis(trifluoromethane)sulfonimide lithium salt in propylene carbonate. With two electrodes placed under the gel, the samples were subjected to a sinusoidal mechanical force while open circuit voltage was measured to determine the relationship between electrical signal and mechanical input. The voltages generated are 10’s of mV in magnitude at 1 kPa. Results suggest a maximum sensitivity of 25 μV/Pa at 10 mHz, comparable to the voltages expected in piezoelectric polymers such as PVDF (44 μV/Pa for similar dimensions). The non-aqueous, solid-state ionic gels presented in this work provide improved stability and is less prone to evaporation than its aqueous, hydrogel based counterpart. The new mechanism of sensing provides an alternative to the more rigid and less stretchable piezoelectric sensors.

Several studies have been reported on the development of controllable catheters in the biomedical field. Electronic conductive polymers (ECP) actuators appeared to be among the most suitable systems thank to their biocompatibility, low operating potential (± 2V) with a reasonable deformation (2%)[1–3]. Electroactive catheters, especially in neurosurgery, should have two levels of properties: strong deformations tip in order to reach, for example the aneurysms and sweep the total volume of the pouch, and sufficient rigid middle part for getting forward in the tortuous vessels network. We designed an electroactive catheter, constituted of two parts with different deformation ability and modulus. The high deformations tip can be obtained with a weak modulus actuator. On the other hand, the second part needs to possess high modulus where small deformations are sufficient. In this work, interpenetrating polymer networks (IPN) will be used as the structural material of the catheter. The IPN architecture allows the synthesis of actuators containing the ions necessary for the redox process and thus avoiding any interference of the position control due to the exchange with the ions from the physiological medium. In addition, the fact that the catheter can be synthesized in a customized way allows modulating its mechanical properties. By introducing a rigid polystyrene network into a specific part of the actuator, it is possible to locally increase the rigidity of the device while keeping reasonable deformation. First, we will describe the synthesis and the characterization of a beam shape actuators with different local stiffnesses. Then, the first steps for the elaboration of tubular actuator will be presented.

Electrochemical actuators operating in open-air are trilayer electrochemical devices based on an ionically conducting membrane sandwiched between two electrodes of electronic conducting polymers (ECP). Tuning functional properties of the actuator, i.e. the output force, is demonstrated via the modification of the ECP’s surrounding macromolecular architecture. Theoretical models have suggested that the output force of trilayer actuators is related to the Young’s modulus of the electrodes. As a consequence, we designed Interpenetrating Polymer Network (IPN) membranes combining three different polymer networks with a co-continuous morphology to act as a host matrix for ECP electrodes. Each of these polymer networks is chosen for a specific role: (i) poly(ethylene oxide) network providing ionic transport medium within the ECP electrodes, (ii) Nitrile Butadiene Rubber providing endurance, flexibility and robustness to the final device and (iii) polystyrene to increase the Young’s modulus of the ECP electrodes. The synthesized IPNs have been thoroughly characterized. The performances of resulting actuators have been assessed. The output force is almost doubled due to the stiffening effect of the polystyrene phase, as predicted by the beam theory.

Ionic resistance is often a rate limiting factor in electrochemical systems such as batteries, supercapacitors, and ionic polymer actuators. Such cells typically contain laminated and interpenetrated structures consisting of one or two electronically conductive layers and an ionically conductive separator layer. Here we analyze the role of electrodes in determining ionic resistance, and study the effects of interpenetrating ionic and electronically conducting phases. We also show that conducting polymer electrodes that are polymerized on separator layers, as have been applied to create actuators, supercapacitors and electrochromic device, can be widely and unevenly distributed through the device. Swept sine and DC measurements are used with a four-point diffusion cell probe to characterize the phase dependent ionic impedances in 1. polypyrrole (PPy) coated polyvinylidene fluoride (PVDF) and 2. poly(ethylene dioxythiophene) (PEDOT) interpenetrated poly(ethylene oxide) (PEO) − nitrile butadiene rubber (NBR) co-polymer with various PEDOT content levels. A finite Warburg-based model is introduced to explain the frequency dependence, enabling a time constant for ion transport within membrane to be estimated. It is found that the separator layers in the composite membranes are shorted at higher frequencies (10 ∼ 100 Hz). This effect is likely due to interpenetration of the electronic phases into the bulk of the separator layers, providing a means of reducing internal resistance and increase power at short times. Finally, a non-uniform impedance distribution model is introduced to predict the effective composite ionic conductivity in terms of the ionic conductivities of each phase, and their non-uniform volume fractions. Taken together, the approaches presented provide a means of probing the influence of ionic conductivities of various phases on the rate of charging in electrochemical devices.

Fast actuation of conducting polymer trilayers has been achieved by reducing the thickness of the device to as little as 6 μm. Reducing size also reduces force and displacement. Here the tradeoffs between speed of response, force and deformation angle are explored, and related to an example application – a tactile feedback interface that aims to make use of the very high sensitivity of our fingertip skin to vibrations of about 150 Hz. In general, the actuation rate in these devices is limited by the speed of charging, and by inertia. Here we use an established transmission line model to simulate charging speed. By making use of the empirical relationship between strain and charge, and using beam bending theory, the extent of charging enables estimation of the degree of actuator deformation and the forces that can be generated. In seeking to achieve non-resonant actuation at frequencies of 150 Hz or more, while also generating the forces and displacements needed for tactile stimulation, it is found that electronic and ionic conductivities of the conducting polymer electrodes needs to be on the order of 24,000 S/m and 0.04 S/m, respectively. These values along with the required dimensions appear to be feasible.

Electrochemical double-layer capacitors (EDLCs) are devices that store enormous amounts of charge electrostatically when a potential is applied between electrodes of very high surface area (typically made of porous carbon) and an electrolyte. Wider commercialization of this technology has been held back by the lack of ultralow-cost electrode materials. We demonstrate that used coffee grounds can be processed to form low-cost electrodes. The surface and electrochemical characteristics of microporous activated carbons from used coffee grounds (CGCs) were measured. First, optimal times and temperatures for carbonization and activation were identified on the basis of Brunauer–Emmett–Teller (BET) surface area, pore volume, and pore size distribution. Second, CGCs were used as polarized electrodes in EDLCs, whose capacitances were evaluated using cyclic voltammetry. The results show that carbonization for 1 h at 600 °C with a heating rate of 300 °C/h, followed by CO2 activation for 2 h at 1000 °C, affords the highest BET surface area (1867 m2/g) compared to other works. The produced CGCs have many micropores of less than 2 nm across, which contribute to the formation of an electric double layer. Capacitors made using these CGCs show the highest capacitance (103 F/g) in 0.8 M (C2H5)4NBF4/PC as an organic electrolyte, which is much higher than the ∼80 F/g typically used in organic-electrolyte-based commercial EDLCs, suggesting that coffee grounds are a useful electrode material. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Highly efficient light absorption and charge separation within the photosystem and reaction center (RC) complexes of photosynthetic plants and bacteria are of great interest for solar cell and photo detector applications, since they offer almost unity quantum yield and expected ultimate power conversion efficiencies of more than 18% and 12%, respectively. In addition, the charge separated states created by these protein complexes are very long lived compared to conventional semiconductor solar cells. In this work, a novel technique is presented for the deposition of photosynthetic protein complexes, by electrospraying RCs of Rhodobacter sphaeroides onto highly ordered pyrolytic graphite (HOPG) electrodes. Remarkably, it is shown that the RCs not only survive exposure to the high electric fields but also yield peak photocurrent densities of up to 7 μA cm−2, which is equal to the highest value reported to date.

The rate of charging of supercapacitor and battery electrodes is often limited by the transport of ions through the active electrode material. One way to accelerate this transport is to increase the porosity of the electrode, at the cost of electrode capacity. This tradeoff is studied through the fabrication and characterization of porous carbon nanofibre/polypyrrole films used as storage electrodes. Electrospun poly (acrylonitrile-co-acrylamide) fibres were carbonized and then electrochemically coated with variable amounts of polypyrrole. The resulting hybrid materials were characterized using both conventional methods such as cyclic voltammetry, electron microscopy and conductivity, as well as ionic conductivity and pulsed-field-gradient nuclear magnetic resonance which directly probe ion transport. It is found that with modest porosity, these materials retain much of the capacitance (∼50%) of bulk polypyrrole with dramatically increased (∼300 times) charge and discharge rates, suggesting the potential of the approach for increasing the useful frequency range of polypyrrole-based supercapacitors, as well as other storage materials whose porosity can be varied. Simple transport models based on series or parallel arrangements of electrolyte and active electrode are developed to explain the results and identify the factors limiting charge/discharge rates.

Electrodes that selectively exchange charge with only certain redox couples in a mixture could improve the performance of photogalvanic and bio-photovoltaic cells described in the literature. One avenue to achieve selectivity is through the use of semiconducting rather than metallic electrodes to exploit the presence of the bandgap to control reaction rates. In this paper, Fluorine doped Tin oxide (F:SnO2), Copper(II) oxide (CuO) and Nickel oxide (NiO) electrodes are investigated as a means to achieving selective redox reactions. The reactions of methyl viologen, ferricyanide/ferrocyanide and ferric/ferrous couples on the three semiconducting electrodes were studied using cyclic voltammetry and sampled current voltammetry. The rate of electron transfer between the electrodes and the redox couples depended on the difference between the semiconductor majority carrier band edge and the standard redox potential of the redox couple. Most noticeably, the rate constant of methyl viologen on F:SnO2 was two orders of magnitude higher than that for the ferric/ferrous ion. Similar results were obtained with the NiO electrode while electrochemical instability hampered the tests of the CuO electrode.

Polypyrrole and other conducting polymers are of interest in actuators, sensors, energy storage devices and organic electronics. The patterning of these polymers can be challenging, particularly polypyrrole due to its insolubility. This paper reports the first micropatterning of polypyrrole using high-frequency pulses of extremely miniaturized electrical discharge. Microstructures with surface roughness of 70 nm are produced in the polymer with sub-micron depth control. Patterning of polypyrrole film deposited on a commercial medical catheter is demonstrated toward enabling smart catheters that use the patterned film as integrated actuators. This novel micropatterning capability opens up new possibilities for polypyrrole and likely other polymers, promoting micro-device applications for them.

Metal nanowires are twisted to form yarns that are strong (0.4 to 1.1 GPa), pliable, and more conductive (3 × 106 S m−1) than carbon nanotube yarns. Niobium nanowire fibers are extracted by etching a copper-niobium nano-composite material fabricated using the severe plastic deformation process. When impregnated with paraffin wax, the niobium (Nb) nanowire yarns produce fast rotational actuation as the wax is heated. The heated wax expands, untwisting the yarn, which then re-twists upon cooling. Normalized to yarn length, 12 deg mm−1 of torsional rotation was achieved along with twist rates in excess of 1800 rpm. Tensile modulus of 19 ± 5 GPa was measured for the Nb yarns, which is very similar to those of carbon multiwalled nanotubes.

International audience; Conducting polymer actuators have long been of interest as an alternative to piezoelectric and electrostatic actuators due to their large strains and low operating voltages. Recently, poly (3,4-ethylenedioxythiophene) (PEDOT) - based ionic actuators have been shown to overcome many of the initial obstacles to widespread application in micro-fabricated devices by demonstrating stable operation in air and at high frequencies, along with microfabrication compatible processing using a layer by layer method that does not require any handling. However, there is still a need for characterization, prediction, and control of the actuator behavior. This paper describes the fabrication and characterization of thin trilayers composed of a 7 mu m thick solid polymer electrolyte (SPE) sandwiched between two 2.1 mu m thick PEDOT-containing layers. Beam properties including capacitance, elastic moduli of the layers, and the extent of charge driven strain, are applied to predict curvature, frequency response and force generation. The actuator is represented by an electrical circuit, a mechanical system described via dynamic beam theory, and a strain-to-charge ratio for the electro-mechanical coupling matrix, which together predict the actuator curvature and the resonant response. The success of this physical model promises to enable design and control of micro-fabricated devices.

There is increasing interest in creating bendable and stretchable electronic interfaces that can be worn or applied to virtually any surface. The electroactive polymer community is well placed to add value by incorporating sensors and actuators. Recent work has demonstrated transparent dielectric elastomer actuation as well as pressure, stretch or touch sensing. Here we present two alternative forms of sensing. The first uses ionically conductive and stretchable gels as electrodes in capacitive sensors that detect finger proximity. In this case the finger acts as a third electrode, reducing capacitance between the two gel electrodes as it approaches, which can be detected even during bending and stretching. Very light finger touch is readily detected even during deformation of the substrate. Lateral resolution is achieved by creating a sensor array. In the second approach, electrodes placed beneath a salt containing gel are able to detect ion currents generated by the deformation of the gel. In this approach, applied pressure results in ion currents that create a potential difference around the point of contact, leading to a voltage and current in the electrodes without any need for input electrical energy. The mechanism may be related to effects seen in ionomeric polymer metal composites (IPMCs), but with the response in plane rather than through the thickness of the film. Ultimately, these ionically conductive materials that can also be transparent and actuate, have the potential to be used in wearable devices.

JIF=2.963; International audience; With the recent growing interest for soft actuation, many new types of ionic polymers working in air have been developed. Due to the interrelated mechanical, electrical, and chemical properties which greatly influence the characteristics of such actuators, their behavior is complex and difficult to understand, predict and optimize. In light of this challenge, an original linear multiphysics finite difference bond graph model was derived to characterize this ionic actuation. This finite difference scheme was divided into two coupled subparts, each related to a specific physical, electrochemical or mechanical domain, and then converted into a bond graph model as this language is particularly suited for systems from multiple energy domains. Simulations were then conducted and a good agreement with the experimental results was obtained. Furthermore, an analysis of the power efficiency of such actuators as a function of space and time was proposed and allowed to evaluate their performance.

A stretchable, transparent touch pad and proximity sensor made using silicone and gel operates while being bent and stretched., The development of bendable, stretchable, and transparent touch sensors is an emerging technological goal in a variety of fields, including electronic skin, wearables, and flexible handheld devices. Although transparent tactile sensors based on metal mesh, carbon nanotubes, and silver nanowires demonstrate operation in bent configurations, we present a technology that extends the operation modes to the sensing of finger proximity including light touch during active bending and even stretching. This is accomplished using stretchable and ionically conductive hydrogel electrodes, which project electric field above the sensor to couple with and sense a finger. The polyacrylamide electrodes are embedded in silicone. These two widely available, low-cost, transparent materials are combined in a three-step manufacturing technique that is amenable to large-area fabrication. The approach is demonstrated using a proof-of-concept 4 × 4 cross-grid sensor array with a 5-mm pitch. The approach of a finger hovering a few centimeters above the array is readily detectable. Light touch produces a localized decrease in capacitance of 15%. The movement of a finger can be followed across the array, and the location of multiple fingers can be detected. Touch is detectable during bending and stretch, an important feature of any wearable device. The capacitive sensor design can be made more or less sensitive to bending by shifting it relative to the neutral axis. Ultimately, the approach is adaptable to the detection of proximity, touch, pressure, and even the conformation of the sensor surface.

We have developed a combined ionic conductivity and temperature sensor package for multiphase chemical reactors, key elements of SmartChip, a flow following, data logging sensor. The initial application of the sensor is to monitor the process inside the hot and caustic chemical environment of a kraft pulp digester (pH ∼ 13, temperatures from 25 to 175 °C, reaching a maximum of 180 °C and pressures up to 2 MPa). The sensor package consists of a 1000 Ω platinum resistance temperature detector (RTD) enclosed in a stainless steel container and a four-electrode conductivity sensor consisting of stainless steel electrodes and installed on a polyetheretherketone (PEEK) package. The sensor package is designed ultimately to move within the kraft pulp digester and record sensor data. The sensors were tested at temperatures of up to 140 °C in NaOH concentrations of 10–100 g/L as Na2O with and without the presence of wood chips. Changes in concentration were clearly discernible as changes in conductivity. The presenc...

Ultrafast laser micromachining was optimized for microstructuring polypyrrole as a facile new approach towards tailoring electrochemical and mechanical responses desirable for microactuator, sensors, neural probing, and nerve conduit applications. Laser perforation of high-density and high aspect ratio through-holes generated greater than 5-fold increase in surface area. The flexible machining technique offers micron-size resolution and fast prototyping capability for optimizing properties and opening new directions for polypyrrole-based devices.

Constant phase elements (CPE) are routinely used to describe the frequency response of electrochemical systems. However, this approach is often scientifically unsatisfactory because the physical origin of the phase is unclear. Here we observe CPE-like behaviour in a conducting polymer poly(3,4-ethylenedioxythiophene)/poly(styrene-4-sulfonate) (PEDOT:PSS) film that was inkjet printed onto paper to form a flexible electrochemical double layer capacitor electrode. We show that the response of the electrochemically active film can also be described using a physical model with multiple parallel finite RC (resistor–capacitor) transmission lines whose lengths and time constants are determined by the distribution of the measured film thickness. The modeled volumetric capacitance and ionic conductivity match those determined experimentally, suggesting that the physical origin of the constant phase response is a distribution of mass transport limited time constants.

Ionically electroactive devices with no encapsulation dry out in air if a solvent-based electrolyte is used, and exchange ions in wet environments, both of which cause the performance of the device to vary over time. In this paper, we investigate the behavior of bare poly(3, 4-ethylenedioxythiophene) trilayer actuators both in intermittent use and continuous cycling in open air and in water, in order to understand how their response changes with time and solvent loss. Not surprisingly, the devices slow as solvent evaporates, but, unexpectedly, the active displacement increases until a large fraction of the solvent is gone. The electrolyte used in these 360 μm thick devices is a 1 M solution of Bis(trifluoromethane)sulfonimide lithium salt (Li+TFSI−) in propylene carbonate (PC). The trilayers lose all their solvent within 8 d, with ~40% loss within a day, when stored in an environment with controlled temperature and relative humidity of (23 ± 2)°C and (50 ± 3)%, respectively. The devices' speeds slow as the PC evaporates from the device (staying within 10% of their initial value after losing ~20% of its PC content). Intermittent testing shows displacement of the device actually increases until only ~14% of the PC content remains which would take almost 4 d if the device is stored in the controlled conditions mentioned above. This is largely due to the reduction of thickness in the trilayers, which then leads to higher curvature. Cycling in open air or in water leads to immediate displacement decrease: dropping 60% over one hour cycling in air and over 12 min cycling in water-due to the reduction of charge transfer rate. Overall, for applications where speed is not critical and operation is only needed for a matter of hours or days, encapsulation may not necessary. We expect that encapsulation will be beneficial to maintain the intermittent operation of the device and to maintain speed for longer periods of use (beyond 4 d and 12 h, respectively in the case studied). Encapsulation should also allow a stable displacement amplitude over time.

In this paper, an analytical model is presented to predict the actuation response of electrochemically driven structures. A 2-D impedance model is first presented that uses a conducting polymer transmission line equivalent circuit to predict the charge transfer during actuation. The predicted electrochemical charging is then coupled to a mechanical model to find the actuation response of a bending structure. The advantage of this model compared to existing models is that it represents the 2-D charging of the polymer, namely through the thickness of the polymer structure and along its length. The model considers both ion “diffusion” through the thickness and electronic resistance along the length. The output of the impedance model is charge density in the polymer as a function of position and time, which is then used to estimate free strain via the strain to charge ratio. Given the modulus of the polymer and of passively deformed structures, time-dependent deformation is then determined. The complete electromechanical model is a function of ionic and electronic conductivities, dimensions, volumetric capacitance, elastic modulus, and strain to charge ratio, all of which are measured independently. The full electromechanical model is shown to provide a good description of the response of bending polymer structures when comparing with experimental results. The model can be effectively used as a design tool for electrochemically driven devices.

Yarns spun by twisting multiwalled carbon nanotubes (MWNTs) have been reported. Here, we report the application of these yarns as mechanical force sensors. When electrochemically charged, the yarns can respond to a change in the applied tension by generating a change in the cell current (up to about 1.2 nA/MPa per centimeter length of the yarn) or the open-circuit potential of the cell (up to 0.013 mV/MPa per centimeter length of the yarn) corresponding to the applied tension force. The MWNT yarns are mechanically strong with tensile strengths reaching 1 GPa. These properties together make them prime candidates for many applications as fast and efficient sensors. Their sensitivity as mechanical strain sensors is about 0.5 V/micorstrain, which is comparable to the sensitivity of metal film strain gauge sensors. The sensitivity is expected to improve by using thicker bundles of yarns.

International audience

An analytical model is presented to describe the electrochemical impedance of conducting polymer based devices. The analytical expression of the impedance is obtained from a two dimensional finite transmission line equivalent circuit. The model relates impedance to cell geometry, electrolyte conductivity, polymer ionic and electronic conductivities and capacitance. These parameters were measured for a hexafluorophosphate (PF6-) doped polypyrrole material (the conducting polymer used in this study) and entered to the model to predict its impedance as a function of frequency. The model is unique in representing the two dimensional charging of the polymer, namely ionic mass transport through the thickness of the polymer structure and electronic resistance along its length. Close agreement is observed between impedance spectroscopy results and model prections of the charging of a polypyrrole film electrically connected at one end. The provides a means of modeling the electrochemical charging of conducting polymers and electrochemical double layer capacitor electrodes having significant ionic and electronic conductivities.

Conducting polymers have been shown to work as force sensors in an electrolyte by generating a voltage or current when the force applied to them is changed. One possible sensing mechanism is the change in the polymer capacitance as a result of an induced tension. This change in capacitance can be related to perturbation of Donnan equilibrium potential by external load. In this paper we present a model using this proposition to predict conducting polymer sensing behaviour. The model also takes the dependence of the sensing voltage on the polymer oxidation state into account. The predicted model results are compared with experimental measurements on a free-standing film of polypyrrole in an aqueous electrolyte of NaPF6. Sensing voltages ranging from ~ 80-110 μV were detected in response to 1.72 MPa change in the polymer stress, when the polymer was at oxidation states of -0.2 V to 0.4 V vs. Ag/AgCl reference electrode. The load-dependent capacitance necessary to induce the observed sensing currents and voltages is determined. The cycle life of the polypyrrole mechanical sensor was also studied and it was shown that after an initial transient period, the sensing current amplitude stays constant for at least 5400 cycles.

In the existing theory for organic field-effect transistors (OFETs) the effect of molecular order on the subthreshold characteristics is ignored. This effect is studied analytically through the potential profile and subthreshold swing at a weak accumulation mode. The developed theory predicts a wide accumulation region and a low subthreshold swing for a poorly ordered semiconductor. Simulation of transistors with various distributions of density of states is performed to mimic OFETs made of regioregular-Poly 3 hexylthiophene (rr-P3HT). The simulation results support the analytical equation for the potential profile. Furthermore, the effect of molecular order on the subthreshold swing matches with the theory. However, the analytical value for the subthreshold swing is greatly underestimated mainly due to an oversimplified model used for mobility.

Squeezing a water droplet between two electrodes can generate a potential difference by converting some of the mechanical energy in vibrations into electrical energy. By utilizing the high capacitance inherent to electric double layers, and the surface charging at a polymer/water interface, we demonstrate a sensor that generates up to 892 mV peak-to-peak between 1 and 100 Hz, in response to a 250 μm deformation. This frequency response is described and explained using a linearized model in which the interfacial charge acts as the priming voltage, removing the need for external charging normally required in capacitive generators. The model suggests how to design the cell for maximum power output and provides an intuitive understanding of the high pass nature of the sensor. It successfully predicts the point of maximum power transfer.

Polypyrrole actuators offer high stresses, moderate strains, low voltage operation and biocompatibility. These materials also act as force and displacement sensors. In this paper the properties of polypyrrole sensors are investigated, enabling the first quantitative demonstration of the link between actuation and sensing, and suggesting a new mechanism of electromechanical coupling that can be exploited in materials that are both ionically and electronically conducting. Polypyrrole actuates when electrochemically charged, with the strain being proportional to the charge density transferred. It has also been shown that applying force to polypyrrole generates a proportional change in voltage. It is shown herein that the same constant of proportionality describes the response in both cases. Based on this finding a semi-empirical model of the electromechanical coupling is proposed. The model suggests that the insertion of ions into the polymer requires mechanical work to elastically deform the matrix. The external application of stress alters the internal stress on ions, helping insert or remove charge, and change voltage. The frequency dependence of the relationship between stress and voltage is also investigated. The sensor response is relatively stable at frequencies between 0.1 Hz and 100 Hz. The results and models presented enable the prediction of polypyrrole sensor and actuator responses.

Electrochemically driven actuation of polypyrrole in aqueous sodium hexafluorophosphate (NaPF 6 ) solution has been shown to produce repeated large strains (>6%) at low voltages and with high conductivity, making it one of the most promising electroactive conducting polymers. Little is known about the voltage dependent stiffness of this version of the polymer. This information is important in determining the strain as a function of load. In this paper the complex Young's modulus (storage and loss components) of a hexafluorophosphate-doped polypyrrole film in aqueous NaPF 6 electrolyte at different oxidation states, under various loads and as a function of the frequency of the applied load, is investigated. Uniformity of doping was ensured by allowing enough time to reach steady state charge levels, and the creep during measurements was minimized by using preconditioning cycles. The results of this study show that storage modulus decreases (from 1 GPa to 0.80 GPa) as the polypyrrole oxidation potential increases (from −0.4 V to +0.4 V versus Ag/AgCl reference electrode). The loss modulus, on the other hand, increases from 55 MPa to 80 MPa. An increasing trend in the Young's modulus is also observed with the applied load. The storage modulus increases from 0.65 GPa to 1 GPa by increasing the applied load from 0.2 MPa to 2.5 MPa. The modulus is found to increase with time through the experiment, which may be due to stretch alignment of the polymer. It is also observed that complex Young's modulus increases in proportion to the logarithm of frequency.

A metallic conductor layer on an elastomeric substrate has a limited stretchability. Application of a conductive rubber layer underneath the metal can enhance the flexibility and preserve the electrical connection even at high strains. Silicone and polydimethyl siloxane (PDMS) have been tested as elastic substrates. A repeatable resistance-strain behavior up to 100% strain is achieved for a multilayer conductor with PDMS substrate. It is found that this type of substrate has a large influence on the size of cracks on the metal layer.

A time-dependent electrochemical and mechanical model of the bending of a conducting polymer actuator-driven structure is presented, and the predicted response is compared with experimental results. The model uses time constants obtained from a transmission line model to describe the electronic and ionic charge transport into the polymer actuator. It then relates the charge transport to the mechanical deflection of the actuator structure. The model is used to predict the time-dependent bending of an active catheter, which is ultimately intended for use in intravascular imaging. A commercial catheter is coated with polypyrrole and laser micromachined into electrodes, which are electrochemically activated, leading to bending of the catheter. The time-dependent bending is compared with the dynamic beam bending model, with measured physical properties including elastic moduli, strain to charge ratio, electronic conductivity, ionic conductivity and capacitance used in the model to successfully describe the dynamics. The results of this comparison are used to determine the primary factors limiting catheter bending speed, and to suggest an optimal polypyrrole geometry and electrochemical parameters in order to achieve faster response. Copyright © 2010 Society of Chemical Industry

Minimally invasive surgical tools using catheter based technology plays an important role in biomedical diagnostics and treatments. Much research has focused on producing an actively controllable tip catheter to improve accuracy and efficiency over traditional passive catheters when navigating inside patients. In this work, we describe the design, fabrication and characterization of a novel laser-micromachined polypyrrole (PPy) based active catheter. Two-dimensional controlled bending motion of a four-electrode catheter is demonstrated. Combining such catheter with optical coherence tomography, which can provide subsurface visualization of biological tissue, imaging capability using the active catheter tip is also demonstrated.

The characterization of the dynamic response (including transfer function identification) of trilayer polypyrrole (PPy) type conducting polymer sensors is presented. The sensor was built like a cantilever beam with the free end stimulated through a mechanical lever system, which provided displacement inputs. The voltage generated and current passing between the two outer PPy layers as a result of the input was measured to model the output/input behavior of the sensors based on their experimental current/displacement and voltage/displacement frequency responses. We specifically targeted the low-frequency behavior of the sensor as it is a relatively slow system. Experimental transfer function models were generated and verified experimentally for sensors with different dimensions. The models can be used to understand the dynamic behavior and sensing ability of the polymers as mechanical sensors. The effect of the active sensor length on the voltage and current outputs has demonstrated that the shorter is the sensor length, the higher are the voltage output and the current passed for the same mechanical input. Also, their current and voltage responses under an impulse displacement stimulus were experimentally measured to show their dynamic sensing response and to estimate the current and voltage sensing bandwidths. Further, an energy balance method has been proposed to estimate the sensor output. Based on the novel experimental and analytical results, the contribution of this study is the first comprehensive investigation into the response analysis and characterization of the PPy-type conducting polymers as mechanical sensors, to the best of authors' knowledge.

The performance of conducting polymers as actuators is determined by a complicated series of molecular processes that occur as a result of oxidation and reduction of the polymer. In particular, the amount of actuation strain generated for a given voltage stimulus is determined by the number and type of ions (and solvent) that enter and leave the polymer and changes in the mechanical properties (particularly elastic modulus) of the polymer. In this paper, we present the effects of cyclic voltammetry on the shear modulus and volume of polypyrrole in two different electrolytes: propylene carbonate and an ionic liquid. An electrochemical quartz crystal microbalance has been used to study simultaneous volume and modulus changes occurring during redox cycling of polypyrrole. The results demonstrate that the modulus generally increases due to oxidation of the polymer, although initial oxidation from the fully reduced state first produces a decrease in modulus followed by a larger increase. The modulus shift and volume changes were smaller in the ionic liquid electrolyte, probably because of the absence of solvent. Comparison of the results obtained in the two electrolytes suggest that interchain interactions dominate in the determination of modulus, so that modulus is higher in the oxidised state even when the polymer is swollen with counterions and solvent.

The use of printing methods to deposit organic semiconductors promises to enable low-cost electronics. However, printing processes deposit thick and amorphous semiconductor layers that result in poorly performing organic field-effect transistors (OFETs) that generally are not appropriate for incorporation into commercially viable circuits. Another undesirable property of OFETs is their high operating voltage (~40 V). Organic metal-semiconductor FETs (OMESFETs) are proposed as alternatives to OFETs for use with printing methods. OMESFETs operate at low voltages (~5 V) and are expected to show better on/off current ratios than OFETs in a thick-film semiconductor. Simulations of OFETs and OMESFETs are performed assuming regioregular poly (3-hexylthiophene) (rr-P3HT) as the amorphous semiconductor layer with localized states close to the band edge. The results of the simulations show a current ratio of 104 in the OMESFET and of 700 in the OFET for a 400-nm-thick semiconductor layer. Because the OMESFET operates in the depletion mode, versus the accumulation mode in the OFET, the calculated mobility in the OMESFET is two orders of magnitude smaller than that in the OFET. Simulations suggest that the OMESFET design offers performance advantages over printable OFETs, where low-voltage operation is demanded.