Bucky-gel laminates are tri-layer structures where polymeric electrolyte film is sandwiched between two compliant electrode layers of carbon nanotubes and ionic liquid. The resulting ionic and capacitive structures, being regarded as a type of electromechanically active polymers (EAP), have the perspective of becoming soft bending actuators in the fields such as biomimetic robotics or lab-on-chip technology. A typical electromechanical step response of a bucky-gel actuator in a cantilever configuration exhibits a fast bending displacement followed by some reverse motion referred to as the back-relaxation. It has been proposed that the bending but also the back-relaxation of bucky-gel laminates occur due to the relocation of cations and anions within the tri-layer structure. A great number of modeling about ionic EAP materials aims to predict the amplitude of free bending or the blocking force of the actuator. However, as the bucky-gel laminates are viscoelastic, the translation from generated force to bending amplitude is not always straightforward – it can take the form of an integro-differential equation with speed (i.e. the amplitude and type of the input signal) and temperature (i.e. the electronic conductivity of the material and driving current) as just some of the parameters. In this study we propose to use a so-called two carrier-model to analyze the electromechanical response of a bucky-gel actuator. After modifying the electrical equivalent circuit, the time domain response of blocking force is measured to elaborate the ionic mechanisms during the work-cycle of bucky-gel actuator.
Electromechanically active polymers (EAP) are considered a good actuator candidate for a variety of reasons, e.g. they
are soft, easy to miniaturize and operate without audible noise. The main structural component in EAPs is, as the name
states, a type of deformable polymer. As polymers are known to exhibit a distinct mechanical response, the nature of
polymer materials should never be neglected when characterizing and modeling the performance of EAP actuators.
Bucky-gel actuators are a subtype of EAPs where ion-containing polymer membrane acts as an electronically insulating
separator between two electrodes of carbon nanotubes and ionic liquid. In many occasions, the electrodes also contain
polymer for the purpose of binding it together. Therefore, mechanically speaking, bucky-gel actuators are composite
structures with layers of different mechanical nature. The viscoelastic response and the shape change property are
perhaps the most characteristic effects in polymers. These effects are known to have high dependence on factors such as
the type of polymer, the concentration of additives and the structural ratio of different layers. At the same time, most
reports about optimization of EAP actuators describe the alteration of electromechanical performance dependent on the
same factors. In this paper, the performance of bucky-gel actuators is measured as a function between the output force
and bending deflection. It is observed that effective stiffness of these actuators depends on the input voltage. This finding
is also supported by dynamic mechanical analysis which demonstrates that the viscoelastic response of bucky-gel
laminate depends on both frequency and temperature. Moreover, the dynamic mechanical analysis reveals that in the
range of standard operation temperatures, tested samples were in their glass transition region, which made it possible to
alter their shape by using mechanical fixing. The mechanical fixity above 90% was obtained when high-frequency input
signal was used to heat the bucky-gel sample.
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.
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.
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.