Janno Torop

Nanoporous carbon-based electrodes for high strain ionomeric bending actuators

Ionic polymer metal composites (IPMCs) are electroactive material devices that bend at low applied voltage (1–4 V). Inversely, a voltage is generated when the materials are deformed, which makes them useful both as sensors and actuators. In this paper, we propose two new highly porous carbon materials as electrodes for IPMC actuators, generating a high specific area, and compare their electromechanical performance with recently reported RuO2 electrodes and conventional IPMCs. Using a direct assembly process (DAP), we synthesize ionic liquid (Emi-Tf) actuators with either carbide-derived carbon (CDC) or coconut-shell-based activated carbon-based electrodes. The carbon electrodes were applied onto ionic liquid-swollen Nafion membranes using a direct assembly process. The study demonstrates that actuators based on carbon electrodes derived from TiC have the greatest peak-to-peak strain output, reaching up to 20.4 me (equivalent to>2%) at a 2 V actuation signal, exceeding that of the RuO2 electrodes by more than 100%. The electrodes synthesized from TiC-derived carbon also exhibit 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.

Ionic electroactive polymer artificial muscles in space applications

A large-scale effort was carried out to test the performance of seven types of ionic electroactive polymer (IEAP) actuators in space-hazardous environmental factors in laboratory conditions. The results substantiate that the IEAP materials are tolerant to long-term freezing and vacuum environments as well as ionizing Gamma-, X-ray, and UV radiation at the levels corresponding to low Earth orbit (LEO) conditions. The main aim of this material behaviour investigation is to understand and predict device service time for prolonged exposure to space environment.

Nanoporous Carbide-Derived Carbon Material-Based Linear Actuators

Devices using electroactive polymer-supported carbon material can be exploited as alternatives to conventional electromechanical actuators in applications where electromechanical actuators have some serious deficiencies. One of the numerous examples is precise microactuators. In this paper, we show for first time the dilatometric effect in nanocomposite material actuators containing carbide-derived carbon (CDC) and polytetrafluoroetylene polymer (PTFE). Transducers based on high surface area carbide-derived carbon electrode materials are suitable for short range displacement applications, because of the proportional actuation response to the charge inserted, and high Coulombic efficiency due to the EDL capacitance. The material is capable of developing stresses in the range of tens of N cm-2. The area of an actuator can be dozens of cm2, which means that forces above 100 N are achievable. The actuation mechanism is based on the interactions between the high-surface carbon and the ions of the electrolyte. Electrochemical evaluations of the four different actuators with linear (longitudinal) action response are described. The actuator electrodes were made from two types of nanoporous TiC-derived carbons with surface area (SA) of 1150 m2 g-1 and 1470 m2 g-1, respectively. Two kinds of electrolytes were used in actuators: 1.0 M tetraethylammonium tetrafluoroborate (TEABF4) solution in propylene carbonate and pure ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMITf). It was found that CDC based actuators exhibit a linear movement of about 1% in the voltage range of 0.8 V to 3.0 V at DC. The actuators with EMITf electrolyte had about 70% larger movement compared to the specimen with TEABF4 electrolyte.

Lifetime measurements of ionic electroactive polymer actuators

This article is focused on proposing a unified methodology for automating the measurement procedures of ionic electroactive polymer actuators. The proposed methodology and large-scale automation would make testing ionic electroactive polymer actuators less labor-intensive and allow analyzing many ionic electroactive polymer actuators simultaneously. Defining a clear framework for testing ionic electroactive polymer actuators performance and reliability would make the testing process reproducible and provide better comparison between ionic electroactive polymer actuators of either different or similar classes. Our methodology separates two types of degradation: degradation during operation and spontaneous self-degradation.

Microporous and mesoporous carbide-derived carbons for strain modification of electromechanical actuators.

Low-voltage stimuli-responsive actuators based on carbide-derived carbon (CDC) porous structures were demonstrated. Bending actuators showed a differential electromechanical response defined by the porosity of the CDC used in the electrode layer. Highly porous CDCs prepared from TiC (mainly microporous), B4C (micromesoporous), and Mo2C (mainly mesoporous) precursors were selected to demonstrate the influence of porosity parameters on the electromechanical performance of actuators. CDC-based bending-type actuators showed a porosity-driven displacement response over a frequency range of 200 to 0.005 Hz at an applied excitation voltage of ±2 V. The displacement response of the CDC actuators increased with an increasing number of mesopores in the electrode layer, and the generated strain of the bending actuators was proportional to the total porosity (micropores and mesopores) of the CDC. The modifiable electromechanical response that arises from the precise porosity control attained through tailoring the CDC architecture demonstrates that these actuators hold great promise for smart, low-voltage-driven actuation devices.

Ionic polymer metal composites with nanoporous carbon electrodes

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 RuO2 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 RuO2 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.

Carbide-derived carbon (CDC) linear actuator properties in combination with conducting polymers

Carbide–derived Carbon (CDC) material is applied for super capacitors due to their nanoporous structure and their high charging/discharging capability. In this work we report for the first time CDC linear actuators and CDC combined with polypyrrole (CDC-PPy) in ECMD (Electrochemomechanical deformation) under isotonic (constant force) and isometric (constant length) measurements in aqueous electrolyte. CDC-PPy actuators showing nearly double strain under cyclic voltammetric and square wave potential measurements in comparison to CDC linear actuators. The new material is investigated by SEM (scanning electron microscopy) and EDX (energy dispersive X-ray analysis) to reveal how the conducting polymer layer and the CDC layer interfere together.

Low voltage linear actuators based on carbide-derived carbon powder

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.

Natural cellulose ionogels for soft artificial muscles

Rapid development of soft micromanipulation techniques for human friendly electronics has raised the demand for the devices to be able to carry out mechanical work on a micro- and macroscale. The natural cellulose-based ionogels (CEL-iGEL) hold a great potential for soft artificial muscle application, due to its flexibility, low driving voltage and biocompatibility. The CEL-iGEL composites undergo reversible bending already at ±500mV step-voltage values. A fast response to the voltage applied and high ionic conductivity of membranous actuator is achieved by a complete dissolution of cellulose in 1-ethyl-3-methylimidazolium acetate [EMIm][OAc]. The CEL-iGEL supported cellulose actuator films were cast out of cellulose-[EMIm][OAc] solution via phase inversion in H2O. The facile preparation method ensured uniform morphology along the layers and stand for the high ionic-liquid loading in a porous cellulose scaffold. During the electromechanical characterization, the CEL-iGEL actuators showed exponential dependence to the voltage applied with the max strain difference values reaching up to 0.6% at 2 V. Electrochemical analysis confirmed the good stability of CEL-iGEL actuators and determined the safe working voltage value to be below 2.5V. To predict and estimate the deformation for various step input voltages, a mathematical model was proposed.

Low-voltage bending actuators from carbide-derived carbon improved with gold foil

We report carbide-derived carbon (CDC) based polymeric actuators for the low-voltage applications. The CDC-based actuators have been designed and fabricated in combination with gold foil. The gold-foil-modified actuators exhibited high frequency response and required remarkably low operating voltage (as low as ±0.25 V). Hot-pressed additional gold layer (thickness 100 nm) ensures better conductivity of polymer supported CDC electrodes, while maintaining the elasticity of actuator. Energy consumption of gold-foil-modified (CDC/gold) actuators increased only at higher frequency values (f > 1 Hz), which is in good correlation with enhanced conductivity and improved charge delivery capabilities. Electrochemical measurements of both actuators performed at small operating frequency values (f < 0.01 Hz) confirmed that there was no difference in consumed charge between conventional CDC and CDC/gold actuators. Due to enhanced conductivity of CDC/gold actuators the accumulated charge increased at higher operating frequency values, while initiating larger dimensional changes. For that reason, the CDC/gold actuators exhibited same deflection rate at much lower potential applied. Electrochemical impedance measurements confirmed that relaxation time constant of gold-foil-modified actuator decreased more than one order of magnitude, thus allowing faster charge/discharge cycles. Gold-foil-modified actuators obtained the strain level of 2.2 % when rectangular voltage ±2 V was applied with frequency 0.5 Hz. The compact design and similar working principle of multi-layered actuator also provides opportunity to use actuator concurrently as energy storage device. From practical standpoint, this device concept can be easily extended to actuator-capacitor hybrid designs for generation of energy efficient actuation.