Conducting polymers are active materials that exhibit an interesting bidirectional electromechanical coupling, where an input voltage results in the displacement of the film and a voltage is produced when a displacement is applied to the film. Mechanical deformation of the transducer by external mechanical loads causes movement of ions, and the generation of voltages. In this work, a dual sensing and actuation model for conducting polymer is described. The model comprises an RC lumped circuit, representing the electrochemical model, a mechanical model described by a dynamic Euler – Bernoulli beam theory, and an empirical strain-to-charge ratio. All three submodels are presented in a self-consistent Bond Graph formalism. The predictions of this model are then demonstrated by comparing with the experimental sensing and actuation results of a 17 µm thin poly(3,4-ethylenedioxythiophene) – based trilayer transducer, showing that the complete electromechanical model elucidates an effective approach to describe both sensing and actuation.
Ionic electro-active polymers (EAP) are promising materials for actuation and sensing. In order to operate in open-air, they are usually built in a trilayer configuration where the internal polymer membrane is soaked with an exogenous electrolyte and sandwiched between two electronic conducting polymer (ECP) layers. The use of exogenous electrolytes can be a limitation in several applications since it may lead to evaporation issues and leakage. Moreover, the soaking step, necessary to introduce the electrolyte in the device, can become tricky as soon as microdevices are considered. In this work we describe the synthesis and characterization of truly “all-solid-state” ionic actuators by using polymeric ionic liquids (PILs). PILs are a new class of polyelectrolytes presenting ionic liquid-like ions along their polymer backbone. First, ECP electrodes containing PIL are synthesized by vapor phase polymerization and their thickness and electronic conductivity are characterized. Then, electrodes and PIL-based membranes are assembled into a trilayer configuration as a proof of concept of solid-state ionic actuator. Under 1.75V, a strain difference about 1% is reached.
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.
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.
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 μm thick solid polymer electrolyte (SPE) sandwiched between two 2.1 μm 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.
The presentation focuses on the performances of flexible all-polymer electroactive actuators under space-hazardous environmental factors in laboratory conditions. These bending actuators are based on high molecular weight nitrile butadiene rubber (NBR), poly(ethylene oxide) (PEO) derivative and poly(3,4-ethylenedioxithiophene) (PEDOT). The electroactive PEDOT is embedded within the PEO/NBR membrane which is subsequently swollen with an ionic liquid as electrolyte. Actuators have been submitted to thermal cycling test between -25 to 60°C under vacuum (2.4 10-8 mbar) and to ionizing Gamma radiations at a level of 210 rad/h during 100 h. Actuators have been characterized before and after space environmental condition ageing. In particular, the viscoelasticity properties and mechanical resistance of the materials have been determined by dynamic mechanical analysis and tensile tests. The evolution of the actuation properties as the strain and the output force have been characterized as well. The long-term vacuuming, the freezing temperature and the Gamma radiations do not affect significantly the thermomechanical properties of conducting IPNs actuators. Only a slight decrease on actuation performances has been observed.
Trilayer actuators enable large mechanical amplification, but at the expense of force. Thicker trilayers can generate more force, but displacement drops. Ideally of course a combination of high force and large displacement is desirable. In this work we explore the stacking of trilayers driven by conducting polymers in order to combine large force and reasonable deflection. Trilayer actuators operating in air are simulated using the finite element method. Force generated and the maximum beam deflection of individual and multiple stacked trilayers are studied in terms of the interface condition of the neighboring layers and the length of the auxiliary trilayer. The best performance is obtained when trilayers are able to slide with respect to each other so forces can add without impeding displacement. This case will require low friction and uniformity among the trilayers. Bonding of stacked trilayers along their entire length increases force, but dramatically reduces displacement. An alternative which leads to moderate displacements with increased force is the use of a long and a short trilayer that are bonded.
This paper presents the synthesis and characterization of thin and ultra-fast conducting polymer microactuators which can operate in the open air. Compared to all previous existing electronic conducting polymer based microactuators, this approach deals with the synthesis of robust interpenetrating polymer networks (IPNs) combined with a spincoating technique in order to tune and drastically reduce the thickness of conducting IPN microactuators using a so-called “trilayer” configuration. Patterning of electroactive materials has been performed with existing technologies, such as standard photolithography and dry etching. The smallest air-operating microbeam actuator based on conducting polymer is then described with dimensions as low as 160x30x6 μm3. Under electrical stimulation the translations of small ion motion into bending deformations are used as tools to demonstrate that small ion vibrations can still occur at frequency as several hundreds of Hz. Conducting IPN microactuators are then promising candidates to develop new MEMS combining downscaling, softness, low driving voltage, and fast response speed.
Electroactive polymers, or EAPs, are polymers that exhibit a change in size or shape when stimulated by an electric field.
The most common applications of this type of material are in actuators and sensors. One promising technology is the
elaboration of electronic conducting polymers based actuators with Interpenetrating Polymer Networks (IPNs)
architecture. Their many advantageous properties as low working voltage, light weight and high lifetime make them very
attractive for various applications including robotics. Conducting IPNs were fabricated by oxidative polymerization of
3,4-ethylenedioxythiophene within a flexible Solid Polymer Electrolytes (SPE) combining poly(ethylene oxide) and
Nitrile Butadiene Rubber. SPE mechanical properties and ionic conductivities in the presence of 1-ethyl-3-
methylimidazolium bis-(trifluoromethylsulfonyl)-imide (EMITFSI) have been characterized. The presence of the
elastomer within the SPE greatly improves the actuator performances. The free strain as well as the blocking force was
characterized as a function of the actuator length. The sensing properties of those conducting IPNs allow their integration
into a biomimetic perception prototype: a system mimicking the tactile perception of rat vibrissae.
We report on new method to obtain micrometric electroactive polymer actuators operating in air. High speed conducting
Interpenetrating Polymer Network (IPN) microactuators are synthesized and fully characterized. The IPN architecture
used in this work allows solving the interface and adhesion problems, which have been reported in the design of classical
conducting polymer-based actuators. We demonstrated that it is possible to reduce the thickness of these actuators by a
specific synthetic pathway. IPN host matrixes based on polyethylene oxide / polytetrahydrofurane have been shaped by
hot pressing. Then, the resulting thin host matrixes (below 10 μm) are compatible with the microfabrication
technologies. After interpenetration of poly(3,4-ethylenedioxythiophene) (PEDOT), these electroactive materials are
micro-sized using dry etching process. Frequency responses and displacement have been characterized by scanning
electronic microscopy. These conducting IPN microactuators can be considered as potential candidates in numerous low
frequency applications, including micro-valves, micro-optical instrumentation and micro-robotics.
A promising alternative of multi-layered devices showing electrochromic properties results from the
design of a self-supported semi-interpenetrating polymer network (semi-IPN) including an electronic conductive
polymer (ECP) formed within. The formation of the ECP in the network has already been described by oxidative
polymerization using iron trichloride as an oxidant and leading to conducting semi-IPN with mixed electronic
and ionic conductivities as well as convenient mechanical properties. This presentation relates to the elaboration
of such semi-IPN using polyethyleneoxide (PEO) network or a PEO/NBR (Nitrile Butadiene Rubber) IPN in
which a linear poly (3,4-ethylenedioxythiophene) (PEDOT) is formed symmetrically and selectively as very thin
layers very next to the two main faces of the film matrix. PEO/PEDOT semi-IPNs lead to interesting optical
reflective properties in the IR between 0.8 and 25 μm. Reflectance contrasts up to 35 % is observed when, after
swelling in an ionic liquid, a low voltage is applied between the two main faces of the film. However the low
flexibility and brittleness of the film and a slow degradation in air at temperature up from 60°C prompted to
replace the PEO matrix by a flexible PEO/NBR IPN one. Indeed, the combination of NBR and PEO in an IPN
leads to materials possessing flexible properties, good ionic conductivity at 25°C as well as a better resistance to
thermal ageing. Finally, NBR/PEO/PEDOT semi-IPNs allow observing comparable reflectance contrast in the
IR range than those shown by PEO/PEDOT semi-IPNs.
In recent years, many studies on electroactive polymer (EAP) actuators have been reported. One promising technology is
the elaboration of electronic conducting polymers based actuators with Interpenetrating Polymer Networks (IPNs)
architecture. Their many advantageous properties as low working voltage, light weight and high lifetime (several million
cycles) make them very attractive for various applications including robotics. Our laboratory recently synthesized new
conducting IPN actuators based on high molecular Nitrile Butadiene Rubber, poly(ethylene oxide) derivative and
poly(3,4-ethylenedioxithiophene). The presence of the elastomer greatly improves the actuator performances such as
mechanical resistance and output force. In this article we present the IPN and actuator synthesis, characterizations and
design allowing their integration in a biomimetic vision system.
Molecular Dynamics (MD) techniques have been used to study the structure and dynamics of a model system of an
interpenetrating polymer (IPN) network for actuator devices. The systems simulated were generated using a Monte
Carlo-approach, and consisted of poly(ethylene oxide) (PEO) and poly(butadiene) (PB) in a 80-20 percent weight ratio
immersed into propylene carbonate (PC) solutions of LiClO4. The total polymer content was 32%, in order to model
experimental conditions. The dependence of LiClO4 concentration in PC has been studied by studying five different
concentrations: 0.25, 0.5, 0.75, 1.0 and 1.25 M. After equilibration, local structural properties and dynamical features
such as phase separation, coordination, cluster stability and ion conductivity were studied. In an effort to study the
conduction processes more carefully, external electric fields of 1×106 V/m and 5×106 V/m has been applied to the
simulation boxes. A clear relationship between the degree of local phase separation and ion mobility is established. It is
also shown that although the ion pairing increases with concentration, there are still significantly more potential charge
carriers in the higher concentrated systems, while concentrations around 0.5-0.75 M of LiClO4 in PC seem to be
favorable in terms of ion mobility. Furthermore, the anions exhibit higher conductivity than the cations, and there are
tendencies to solvent drag from the PC molecules.
This paper presents a new way to design and fabricate ionic polymer actuators showing a linear movement in air. This is done by use of an original shaping during the polymerization step. The possible solutions for linear actuation were tested with a simulation technique that has been designed on purpose, which helped us to choose the best. By means of very unusual fabrication techniques that were required for that, actuators were made following this principle and their performances were measured.
In order to solve the interface and adhesion problems encountered with multilayered actuators, IPN based actuators are presented. The IPNs are synthesized between poly(ethylene oxide) and polybutadiene networks in which the conducting polymer (poly(3,4-ethylenedioxythiophene)), PEDOT, is gradually dispersed i.e. the content decreases from the outside towards the center of the film. The conducting IPN morphology was investigated by DMA and microscopy. The choice of the solid polymer electrolyte system is critical when operating in air. Aqueous solution or organic solvents containing electrolytes were first used, but drying failure could not be prevented. The most promising results are obtained with a room temperature ionic liquid, 1-ethyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide (EMITFSI). During the redox reactions involving PEDOT in EMITFSI, a cation transfer mechanism occurred. Moreover, the bis-(trifluoromethylsulfonyl)imide anion behaves as a plasticizing agent for the IPN matrix. We observed that no degradation of the conducting polymer and no drying process occurred during period as long as 3 months. These actuators can achieve more than 7 E6 bendings from 1 to 18 Hz under applied potential from 2 to 5 V
A new approach is proposed, namely the use of Interpenetrating Polymer Networks (IPNs) in order to solve the interface and adhesion problems in the design of classical conducting polymer based actuators. Semi IPN type materials are synthesized between poly(3,4-ethylenedioxythiophene) and a poly(ethyleneoxide) based network as the ionic conducting partner. The synthetic pathway which will be presented ensures a gradual dispersion of the electronic conducting polymer through the thickness of the material i.e. the content decreases from the outside towards the center of the film. The system is thus similar to a layered one with the advantage that the intimate combination of the two polymers needs no adhesive interface. The influence of the morphology and chemical composition of the matrix on the electronic conductivity of the material have been studied. The surface conductivity can reach 15 S/cm. Finally, this material is capable of a 45 degree(s) angular deflexion under a 0.5 V potential difference.