The ionic electroactive polymer (IEAP) actuators are the type of smart material that is capable of generating large deformations on the application of a small potential across the electrodes. In addition, the IEAP actuators with ionic liquid as an electrolyte are capable of operating in an open-air environment. These aspiring characteristics put forward these actuators to be a promising candidate for replacing traditional actuators in micro-actuation applications. The CPC actuators are distinguished from other types of IEAP’s by the presence of porous carbon as an electrode material and an ionic liquid as electrolyte. In this work we propose design and fabrication of a multi-degree freedom motion platform based on four carbon-polymer composite (CPC) actuators. The complete platform is fabricated as a single structure with appropriate masking. This motion system is highly dexterous and is capable of generating three different motion namely tip, tilt and piston motion. The experiment results have demonstrated high levels of manipulability from the CPC actuators that are outstanding in the class of soft ionic actuators while keeping the fabrication method simple, scalable and cost-effective.
The ionic electroactive polymer (IEAP) actuators with carbonaceous electrodes and ionic liquid electrolytes are distinguished by their ability for operation in open air. Nevertheless, their behavior is influenced by at least two parameters of the ambient environment – temperature and humidity. Both parameters affect many factors of the IEAP materials: viscosity and ionic conductivity of the electrolyte, specific capacitance of the electrodes, stiffness of the polymer, etc. This circumstance makes it difficult to comprehend the actual physical and electrochemical processes occurring in the IEAP materials as well as hinders the control of the actuators in the possible applications. This work is focused on characterizing the temperature and humidity-dependence of the electromechanical and electrochemical response of IEAP actuators. An extensive experiment was performed with several types of IEAP actuators in a temperature- and humidity-controlled environment. The characterization of electrical and electromechanical response measurements were carried out at temperatures ranging from 0°C to +60°C and relative humidity ranging from 0% to 90%. The result showing that impact of both parameters on IEAP actuators is easily recognizable.
Ionic electroactive polymer (IEAP) actuators with carbon based porous electrodes and ionic liquid electrolyte are attractive alternatives compared to the actuators composed of noble metal electrodes. Besides of numerous other parameters, the porosity of the electrode matrix has high influence on the electrochemical behavior and mechanical response of these actuators. Porosity has direct influence on the tortuosity, electronic conductivity, ionic conductivity, ion diffusivity, mobility, as well as the specific area and specific capacitance of electrode. It can also influence directly the mechanical properties of the IEAP laminate: durability, stiffness, etc. In this study, a detailed physical model that incorporates porosity of electrodes and its relation to the electrochemical, transport and mechanical behavior of the IEAP actuator is developed. The behavior of the actuator under different porosity values is investigated through finite elements simulation. The outputs of the simulation are cation concentration, current consumed and deformation of the actuator etc. Altering porosity and determining its optimum value help to comprehend the occurring physical and electrochemical processes, as well as to design actuators capable of delivering optimum electrical and mechanical response.
In order to diminish the effect of terminals to the aqueous ionic electroactive polymer (IEAP) actuators, the electrical input terminals should be made of a noble metal – platinum or gold. In any case, they should not be made of copper. As a matter of fact, copper is electrochemically not stable enough, even at very low voltages. As soon as a voltage is applied between the terminals, the ions of copper formed in the process of oxydation migrate very fast into the IEAP. The bending of IEAP actuators is caused by the movement of cations in the applied electric field. In the region of electrical terminals the infiltrated cations of copper will participate in this process and give additional effect. With the help of a showy experiment we compare the bending of a water-swollen ionic polymer membrane using terminals made of copper and made of gold. The experiment demonstrates impressively, that the copper ions originated from the copper contacts cause bending close to the terminals, and alter the composition of the membrane between the terminals.
We present a novel experimental method for qualitative visualization and quantitative characterization of the time-dependent behavior of bending ionic electroactive polymer actuators. The thin fibers, attached to the actuator, represent the surface normal at the given points of the bending actuator. The structure, formed by the skeleton of many adjacent fibers, amplifies the visual overview about the whole actuator. The four coordinates formed by four tips of two fibers enable determining the axial as well as the bending strains of a bending actuator.
Depending on the electrode material and on the cations, the electrolysis of water starts at significantly higher voltages than the standard potential of the water electrolysis cell, which is 1.23V. We present the simple methodic of determining the "safe" voltage of aqueous IPMCs below what there is no water electrolysis, with the corresponding quantitative data. Higher voltages applied to IPMC cause irreversible formation of platinum oxides and absorption of hydrogen on the platinum electrodes that can change the mechanism of water electrolysis and decrease the minim required voltage of water electrolysis even below the 1.23V.
This work reports on the modelling and control of ionic electroactive polymer actuators with electrodes based on nanoporous carbon, which are working in ambient environment. The model incorporates the humidity level value as one of the input parameters, and so captures the environment-dependent dynamics of the actuator. The effect of ambient humidity on the actuators is studied through the frequency response analysis and is followed by neural network method of modelling. A closed loop set point tracking control system based on gain scheduled model predictive control is designed and developed for position control of actuator and is verified experimentally. The developed model and controller is capable to predict and control the actuators at under the humidity conditions varying in the range of 3% - 97%.
Ionic electroactive polymers or IEAPs are considered as an attractive actuators and sensors in various applications. Many of these polymer composites are designed to be used in an ambient environment. However, the ambient conditions may significantly vary depending on the seasonal or the geographical irregularities generated by the power of nature. <p> </p>Taking the advantage of the fluctuating weather conditions of Estonia, different IEAP materials were continuously monitored for about 6 weeks. During this time the temperature and relative humidity of the ambient environment varied between 30-58 % and 23-29 °C respectively. The experiment was conducted in a non-air-conditioned lab facility where the parameters such as temperature, humidity, atmospheric pressure were registered. Concurrently the electromechanical impedance of 12 actuators of different types was registered. This setup brings out the degradation as well as the impact of the environment to the IEAP actuators. The analysis reveals that the performance of the actuators under research is highly correlated with the ambient relative humidity level which can increase or decrease their performance more than 2 times. Naturally, this issue needs to be addressed in characterization, modeling and control areas. In contrast, the changes of pressure and temperature appeared to have no significant influence on the performance of the actuators investigated
Ionic electroactive polymer (IEAP) laminates are often considered as perspective actuator technology for mobile robotic appliances; however, only a few real proof-of-concept-stage robots have been built previously, a majority of which are dependent on an off-board power supply. In this work, a power-autonomous robot, propelled by four IEAP actuators having carbonaceous electrodes, is constructed. The robot consists of a light outer section in the form of a hollow cylinder, and a heavy inner section, referred to as the rim and the hub, respectively. The hub is connected to the rim using IEAP actuators, which form ‘spokes’ of variable length. The effective length of the spokes is changed via charging and discharging of the capacitive IEAP actuators and a change in the effective lengths of the spokes eventuate in a rolling motion of the robot. The constructed IEAP robot takes advantage of the distinctive properties of the IEAP actuators. The IEAP actuators transform the geometry of the whole robot, while being soft and compliant. The low-voltage IEAP actuators in the robot are powered directly from an embedded single-cell lithium-ion battery, with no voltage regulation required; instead, only the input current is regulated. The charging of the actuators is commuted correspondingly to the robot’s transitory position using an on-board control electronics. The constructed robot is able to roll for an extended period on a smooth surface. The locomotion of the IEAP robot is analyzed using video recognition.
The high spatial, temporal, and thermal resolution of the thermal imaging system Optotherm EL InfraSight 320 is used for investigation of the thermal behavior of the ionic electroactive polymer (IEAP) actuators. The resolution of 10-20 pixels in the direction of their thickness is close to the theoretical limit restrained by the infrared light wavelength registered by the imaging system. The videos, recorded with the frame rate of 30 fps, demonstrate showy the propagation of heat along the membrane. The analysis of the thermal images provides the foundation for precise modeling of the IEAP actuators, taking into account the thermally induced mechanical and electrochemical effects. Experiments conducted with the IEAP actuators of different types (ionic polymer-metal composite, carbon-polymer composite, conducting polymer actuators) allow comparing their efficiencies. The experiments show demonstrable, that the IEAPs, used improperly, overheat to the inadmissible temperatures within seconds only. This, in turn, evaporizes the volatile electrolyte, and shortens the life expectancy of the IEAP devices.
Commonly, modeling of the bending behavior of the ionic electroactive polymer (IEAP) actuators is based on the classical mechanics of cantilever beam. It is acknowledged, that the actuation of the ionic electroactive polymer (IEAP) actuators is symmetric about the centroid - the convex side of the actuator is expanding and the concave side is contracting for exactly the same amount, while the thickness of the actuator remains invariant. Actuating the IEAP actuators and sensors under scanning electron microscope (SEM), in situ, reveals that for some types of them this approach is incorrect. Comparison of the SEM micrographs using the Digital Image Correction (DIC) method results with the precise strain distribution of the IEAP actuators in two directions: in the axial direction, and in the direction of thickness. This information, in turn, points to the physical processes taking place within the electrodes as well as membrane of the trilayer laminate of sub-millimeter thickness. Comparison of the EAP materials, engaged as an actuator as well as a sensor, reveals considerable differences between the micro-mechanics of the two modes.
The research is focused on lifetime and degradation of ionic electroactive polymer actuators (IEAP). The lifetime measurements were carried out using identical methodology upon the different IEAP types. The experiment conducted with large number of samples shows that two types of degradation have serious effect to the IEAPs: degradation during operation and spontaneous self-degradation. Additionally, two ways of occasional damage decrease their overall reliability. In the scope of the current paper we describe degradation of two different types of IEAP actuators: with carbonaceous electrodes and with conducting polymer electrodes. Nevertheless, the common evolutionary trends, rather than the comparative data analysis or formal statistics of all particular samples, are given. Analyzing the electromechanical and electrical impedances of the samples during their whole lifetime, we have found that observing the electric current gives adequate information about the degradation level of any IEAP actuator. Moreover, tracking this electrically measurable parameter enables detecting the occasional damage of an actuator.
Comparative measurements of carbon-polymer composite micro-actuators based on room temperature ionic
liquid electrolyte were carried out in situ (1) in vacuum using a state-of-the-art scanning electron microscope, (2)
in an oxygen-free atmosphere under ambient pressure, and (3) under ambient environment. The fabricated
micro-actuators sustained their actuation performance in all three environments, revealing important implications
regarding their humidity-dependence. SEM observations demonstrate high stroke actuation of a device with submillimeter
length, which is the typical size range of actuators desirable for medical or lab-on-chip applications.
To perform tasks such as hold an object with a constant force, the reliable control of an ionic electroactive polymer
actuator is essential. The composite under research is an IPMC actuator with electrodes composed of nanoporous carbon
and membrane made of ionic polymer. Compared to traditional platinum electrodes, these novel electrodes do not crack
in clusters and have highly controllable properties which preserve even when the actuator is deformed. So far, there are
no reports on the dynamic force response of this composite. We present the first attempts of testing the force dynamics
of an IPMC with nanoporous carbon electrodes under open- and closed-loop controls. As many attempts have been
focused on the sensorless force control of ionic electroactive polymers, we first investigate the uncompensated dynamics
of the actuator, then use the direct inverse model to obtain the desired tracking performance. We also aim to identify the
conditions, under which the actuator is suitable for sensorless control. Furthermore, we improve the tracking ability of
the actuator using a feedback controller where the force sensor data is available and incorporate a feedforward controller
into the feedback control system. Based on the experiments, the resulting effects on the tracking performance are
The autofocus fluid lens device, as developed by Philips, is based on water/oil interfaces forming a spherical lens where
the meniscus of the liquid can be switched by applying a high voltage to change from a convex to a concave divergent lens. In this work we construct a device to evaluate the performance of membrane actuators based on electro active
polymers, in a design applicable for autofocus fluid lens applications. The membrane with a hole in the middle separates
the oil phase from the electrolyte phase, forming a meniscus in the middle of the membrane between the oil and
electrolyte. If the membrane actuator shows a certain force and displacement, the meniscus between oil and electrolyte changes form between concave and convex, applicable as a fluid lens. Ionic polymer metal composites (IPMCs) are applied in this work to investigate how the performance of the membrane actuator takes place in Milli-Q, certain
electrolytes and in combination with an electrochemically deposited conducting polymer. The goal of this work is to
investigate the extent of membrane displacement of IPMC actuators operating at a low voltage (±0.7 V), and the back relaxation phenomena of IPMC actuators.
One of the constraining properties of the IPMC actuators is their back-relaxation. An excited IPMC actuator, instead of holding its bent state, relaxes back towards its initial shape even when the exciting signal is a DC voltage. This behavior is reported by many authors and is usually explained with diffusion of water back, or out of the electrodes. However, a non-traditional approach to the well-known elements of the traditional viscoelastic schemes – spring and damper – results with a qualitatively new model of viscoelasticity. This mechanical analogy of viscoelastic behavior elucidates the naturalness of the back-relaxation behavior of the actuators. The model is described by a system of PDEs and gives an intuitive and accurate charge-deflection correlation with back-relaxation included. The experiments carried out with actuators of different shapes show excellent accordance with the model.
In comparison to other ionic electromechanically active polymers (ionic EAP), carbon-polymer composite (CPC) actuators are considered especially attractive due to possibility of producing completely metal-free devices. However, mechanical response of ionic EAP-s is, in addition to voltage and frequency, dependent on environmental variables such as humidity and temperature. Therefore, similarly to other EAPs, one of the major challenges lies in achieving controlled actuation of the CPC sample. Due to their size and added complexity, external feedback devices (e.g. laser displacement sensors and video cameras) tend to inhibit the application of micro-scale actuators. Hence, self-sensing EAP actuators – capable for simultaneous actuation and sensing – are often desired. A thin polyvinylidene fluoride-cohexafluoropropylene film with ionic liquid (EMIMBF<sub>4</sub>) was prepared and masked coincidently on opposite surfaces prior to spray painting carbide-derived carbon electrodes. The purpose of masking was to create different electrically insulated electrodes on the same surface of polymer in order to achieve separate sections for actuator and sensor on one piece of CPC material. Solution of electrode paint consisting of carbide-derived carbon, EMIMBF<sub>4</sub> and dimethylacetamide was applied to the polymer film. After removing the masking tape, a completely metal-free CPC actuator with sophisticated electrode geometry was achieved to foster simultaneous sensing and actuation, <i>i.e.</i> self-sensing carbon-polymer actuator was created.
High surface area carbon, ionic liquid and polymer are incorporated in an electromechanically active composite. This
laminate bends when voltage (typically less than 3 V) is applied between the electrodes, and generates voltage and
current when bent with an external force. By suitable optimization, the material can be used either as an actuator, energy
storage element (supercapacitor) or sensor. Strain caused by bending promotes dislocation of ions in the micropores of
carbon. As a result, the charge separation occurs because ions of ionic liquid are likely trapped in the micropores of
diameters close to the ion sizes.
The paper describes a simple and cost-effective design and fabrication process of a liquid-filled variable-focal lens. The
lens was made of soft polymer material, its shape and curvature can be controlled by hydraulic pressure. An electroactive
polymer is used as an actuator. A carbon-polymer composite (CPC) was used. The device is composed of elastic
membrane upon a circular lens chamber, a reservoir of liquid, and a channel between them. It was made of three layers
of polydimethylsiloxane (PDMS), bonded using the partial curing technique. The channels and reservoir were filled with
incompressible liquid after curing process. A CPC actuator was mechanically attached to reservoir to compress or
decompress the liquid. Squeezing the liquid between the reservoir and the lens chamber will push the membrane inward
or outward resulting in the change of the shape of the lens and alteration of its focal length. Depending on the pressure
the lens can be plano-convex or plano-concave or even switch between the two configurations. With only a few minor
modifications it is possible to fabricate bi-convex and bi-concave lenses. The lens with a 1 mm diameter and the focal
length from infinity to 17 mm is reported. The 5x15mm CPC actuator with the working voltage of only up to ±2.5 V was
capable to alter the focal length within the full range of the focal length in 10 seconds.
We present the design, fabrication process and characterization of multilayer miniaturized polydimethylsiloxane
(PDMS)-based dielectric elastomer diaphragm actuators. The conductive stretchable electrodes are obtained by lowenergy
metal ion implantation. To increase force, decrease the required voltage, and avoid dielectric breakdown, we
present here a technique to fabricate multilayer devices with embedded electrodes with complex shapes. By implanting
electrodes on a partially cured PDMS film, then casting on it the next layer of PDMS, it is possible to have the compliant
electrodes "molded" inside PDMS. Using custom shadow masks allows defining electrodes of any shape or size, we
report sizes down to 0.1 mm. The minimal distance between independent electrodes inside the PDMS is limited solely by
the breakdown voltage of PDMS and can be also as small as 0.1 mm. Using this approach, we have fabricated miniature
compact devices consisting of several independent dielectric elastomer actuators on a single PDMS film. Applying
different voltages to the separate actuators allows to achieve complicated movements of the whole device, e.g. to act as a
3-DOF parallel manipulator. A distinctive feature of the multi-layer actuators is that they attain similar strain with lower
voltage than the single-layer actuators of the same thickness. We report on a 3 mm diameter 2-axis beam steering device
combining three actuators.
CPC (carbon-polymer composite) is a type of low voltage electromechanically active material, which is often built using
two layers of electrodes containing nanoporous carbon separated by a thin ion-permeable polymer film; ionic liquid is
used as electrolyte. In cantilever configuration, while low voltage (3 V) is applied to these electrodes, the CPC sheet
To date, virtually no research into sensing properties of these materials has been conducted. In order to determine the tip
displacement (curvature) of the CPC actuator, change of surface resistance in the process of bending is measured. Within
the scope of this paper, it is also to investigate whether the acquired signals are feasible for use as a feedback to the
actuator's driving mechanism and thus creating a self-sensing CPC device. Experimental data is presented to report that
both resistive and capacitive effects are present on surface electrodes and alter during the actuator's work-cycle.
Ionic Polymer Metal Composites (IPMCs) are soft electroactive polymer materials that bend in response to the voltage
stimulus (1 - 4 V). They can be used as actuators or sensors. In this paper, we introduce two new highly-porous carbon
materials for assembling high specific area electrodes for IPMC actuators and compare their electromechanical
performance with recently reported IPMCs based on RuO<sub>2</sub> electrodes. We synthesize ionic liquid (Emi-Tf) actuators
with either Carbide-Derived Carbon (CDC) (derived from TiC) or coconut shell based activated carbon electrodes. The
carbon electrodes are applied onto ionic liquid-swollen Nafion membranes using the direct assembly process. Our results
show that actuators assembled with CDC electrodes have the greatest peak-to-peak strain output, reaching up to 20.4 mε
(equivalent to >2%) at a 2 V actuation signal, exceeding that of the RuO<sub>2</sub> electrodes by more than 100%. The electrodes
synthesized from TiC-derived carbon also revealed significantly higher maximum strain rate. The differences between
the materials are discussed in terms of molecular interactions and mechanisms upon actuation in the different electrodes.
This paper presents a realization of a self-sensing ionic polymer-metal composite (IPMC) device by patterning its surface
electrodes and thus creating separate actuator and sensor parts. The sensor and actuator elements of such device are still
electrically coupled through the capacitance and/or conductivity of the ionic polymer. By creating a separate grounded
shielding electrode between the two parts, it is possible to suppress significantly the undesired cross-talk from the
actuator to the sensor. The paper at hand compares three different methods for separating sensor and actuator parts:
manual scraping, machine milling, and laser ablation. The basis of comparison of the methods is the electrical
characteristics of the device after realizing the surface patterns and the convenience of manufacturing.
The bending actuation of IPMCs is caused by the electrochemical reactions under imposed electric fields. The bending
properties of the IPMC actuators as well as the sensitivity of IPMC sensors depend on the several particular impedances
of the material, e.g. the conductivity of the electrodes, the capacitance of the ionomer, etc. The variation of the shape of
the IPMCs causes the variations of those impedances and, therefore, leads to changes in their behavior. This effect is
important in understanding the behavior of IPMC devices and could be exploited to obtain the feedback signal from
This paper presents the results of the measurements of variations of the impedances of the surface electrodes as well as
the IPMC devices in full during the course of their bending depending on the curvature of the device. The
electrochemical analyses, including voltammetry and electrochemical impedance spectroscopy were carried out with two
different IPMC materials. We show that the dynamical mechanical properties of the bending IPMC device and the
particular impedances are correlated.
Novel linear electromechanical actuators based on nanoporous TiC-derived carbons were prepared and studied.
Traditionally, thin membranes containing mobile ions are used for bending actuators. We describe a linear actuator
which consists of carbon material thin film and an ionic liquid. The thin film is made from nanoporous TiC-derived
carbon powder and polytetrafluoroethylene (PTFE) as a binder agent. The working mechanism of the actuators is based
on the interactions between the high-surface-area carbide-derived carbon (CDC) and the ions of the electrolyte. These
actuators are able to generate linear actuation of about 1% from their thickness under voltages less than 3 V. The motion
starts already at 0.8V and the magnitude of actuation depends on the electrical charge stored by the device. Two different
types of electrolyte were used: 1) Ionic liquid (EMITf) and 2) Tetra-alcyl-ammonium salt in propylene carbonate (PC)
solution. The actuators with ionic liquid have 60% higher movement. The electromechanical parameters of the actuators
were studied by using cyclic voltammetry and electrochemical impedance spectroscopy methods.
This paper presents a distributed model of an IPMC (Ionomeric Polymer-Metal Composite). Unlike other
electromechanical models of an IPMC, the distributed nature of our model permits modelling the non-uniform bending
of the material. Instead of modeling solely the tip deflection of the material, we model the changing curvature. Our
model of the IPMC describes the actuator or sensor as a distributed one-dimensional RC transmission line. The behavior
of the IPMC at its each particular position in time-domain is described by a system of Partial Differential Equations.
(PDE). The parameters of the PDE-s have a clear physical interpretation: the conductivity of the electrodes, the
pseudocapacitance of the arising double-layer at the boundary of the electrodes, the electric current caused by electrode
reactions etc. The electromechanical coupling between the electrical parameters and the bending motion is implemented
by means of distribution of electric current along the material in a time domain. The distributed nature of the model
permits predicting the non-uniform bending of the IPMC actuators in time domain or to reconcile the output of an IPMC-based
position sensor with its shape. Taking into account several nonlinear parameters, the model is consistent with the
experimental results even when the inflexion of the actuator or sensor is large or the water electrolysis appears.
Composite actuators consisting of sheets of the solid polymer electrolyte (similar to Nafion<sup>(R)</sup>) with Cu<sup>2+</sup> counter-ions
inserted and coated with platinum and copper metal layers (so-called Ionomeric Polymer-Metal Composites; IPMCs)
have been synthesised and their electromechanical performance upon actuation has been monitored. Resistance
measurements on the electrodes show that the electrical conductivity of the membranes metal surface increases on the
cathode side during the actuation process, contradictory to the situation when Cu is absent from the metal coating. This
phenomenon is explained by the subsequent reduction of Cu<sup>2+</sup> ions on the cathode upon actuation; Cu layer growth in
this side prevents it from cracking and decreases its electrode resistance. The phenomenon opens up for longer life-times
for Cu-based IPMCs. However, additional problems with Cu layer oxidation and Cu dendrite growth on the electrodes
should be considered.
IPMC (Ionic Polymer Metal Composite) is a class of electroactive polymers (EAP) that bend when electric field is
applied to the material. From our theoretical studies of the material it appears that IPMC can be modelled as a lossy
transmission line. From simulations it appears that IPMC reaction time depends on length of the strip used. Also the
shorter the transmission line the less complex it is to model. We have also mechanically modeled an IPMC. It appears
that the output force does not depend on length on IPMC but on width. Also the shape unpredictability is the larger the
longer the strip is. Based on these results the concept of a short IPMC with rigid extension was created. From
simulations and experiments it was seen that there exists a certain length of IPMC at which output force and deflection
angle remain close to those of a long IPMC while precision increases. Also, the material becomes easier to model and its
short-term stability appears to be sufficient to be controlled. A manipulator was built to verify IPMC compatibility as
links, tested for accuracy and compared with a long sheet of IPMC. The manipulator appeared to be 314% more accurate
and twice as fast compared to the long strip of an IPMC and thus confirming the usability of the described design.
We study ionomeric polymer-metal composite (IPMC) actuators in situations where the strip of actuator acts either on maximum mechanical power or maximum amplitude of actuation. We apply a modified equivalent circuit of IPMC muscle which takes into account the surface resistance change while material bends. In case of series of bending acts, the first actuation of IPMC actuator is performed by a relaxed actuator, it bends over it's full length. During the next movements the most of the energy is caught by fore-part of actuator. The explanation of that effect is given.