Andres Punning

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.

A self-oscillating ionic polymer-metal composite bending actuator

This paper presents an electromechanical model of an ionic polymer-metal composite (IPMC) material. The modeling technique is a finite element method (FEM). An applied electric field causes the drift of counterions (e.g., Na+), which, in turn, drags water molecules. The mass and charge imbalance inside the polymer is the main cause of the bending motion of the IPMC. The studied physical effects have been considered as time dependent and modeled with FEM. The model takes into account the mechanical properties of the Nafion polymer as well as the thin coating of the platinum electrodes and the platinum diffusion layer. The modeling of the electrochemical reactions, in connection with the self-oscillating behavior of an IPMC, is also considered. Reactions occurring on the surface of the platinum electrode, which is immersed into formaldehyde (HCHO) solution during the testing, are described using partial differential equations and also modeled using FEM. By coupling the equations with the rest of the model, ...

A Distributed Model of Ionomeric Polymer Metal Composite

This article presents a novel model of an ionomeric polymer metal composite (IPMC) material. An IPMC is modeled as a lossy RC distributed line. Unlike other electro-mechanical models of an IPMC, the distributed nature of our model permits modeling the non-uniform bending of the material. Instead of modeling the tip deflection or uniform deformation of the material, we model the changing curvature. The transient behavior of the electrical signal as well as the transient bending of the IPMC are described by partial differential equations. By implementing the proper initial and boundary conditions we develop the analytical description of the possibly non-uniform transient behavior of an IPMC consistent with the experimental results.

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.

Mechanical interpretation of back-relaxation of ionic electroactive polymer actuators

The mechanical model obtained by a non-traditional approach to the basic components of the traditional viscoelastic models—spring and damper—elucidates the back-relaxation of ionic electroactive polymer actuators. The corresponding PDE characterizes the curvature or bending moment of the actuators throughout stimulated bending forward followed by relaxation back towards the initial shape. Combining series of short entities containing the lumped electrical circuit, and the transient bending moment generated according to the PDE, results in a new model of the ionic electroactive polymer actuators. This model takes into account the back-relaxation of the actuators as well as the superposition principle. The experiments carried out with three actuators of different ionic electroactive polymer materials show excellent accordance with the model.

A mechanical model of a non-uniform ionomeric polymer metal composite actuator

This paper describes a mechanical model of an IPMC (ionomeric polymer metal composite) actuator in a cantilever beam configuration. The main contribution of our model is that it gives the most detailed description reported so far of the quasistatic mechanical behaviour of the actuator with non-uniform bending at large deflections. We also investigate a case where part of an IPMC actuator is replaced with a rigid elongation and demonstrate that this configuration would make the actuator behave more linearly. The model is experimentally validated with MuscleSheet™ IPMCs, purchased from BioMimetics Inc.

A linked manipulator with ion-polymer metal composite (IPMC) joints for soft- and micromanipulation

IPMCs are electroactive materials that bend in electric field. This paper describes a linked manipulator using IPMC joints. We argue that this design reduces the control complexity of an IPMC manipulator and increases the precision of the device. The design rationale stems from our theoretical work in material modeling. It suggests that when electrically decoupled short IPMC strips are connected to rigid links, the control of the IPMC manipulator, which is currently vaguely understood and highly non-linear, can be reduced to simple inverse kinematics serial chain manipulator control without the loss in efficiency. We validate our design by comparing the prototype device to a simple IPMC manipulator commonly investigated in the literature. The results show increased precision, reaction time and reachable workspace. We suggest that such a manipulator is suitable for soft and micromanipulation.

Electromechanical model for a self-sensing ionic polymer–metal composite actuating device with patterned surface electrodes

This paper further discusses a concept of creating a self-sensing ionic polymer–metal composite (IPMC) actuating device with patterned surface electrodes where the actuator and sensor elements are separated by a grounded shielding electrode. Different patterning methods are discussed and compared in detail; the presented experimental data give an understanding of the qualitative properties of the patterns created. Finally, an electromechanical model of the device is proposed and validated.

In situ scanning electron microscopy study of strains of ionic electroactive polymer actuators

We have developed a technique to determine the bending strain of ionic electroactive polymer actuators without the use of the macroscopic bending geometry. In situ comparisons of the scanning electron microscope micrographs from a bending ionic electroactive polymer actuator, using a digital image correction methodology, identify its bi-directional deformation field. The developed technique allows verification of the factual axial and thickness strains of any notional layer of the actuator, including the outer surfaces of the electrodes. Thus, calculation of the bending and thickness strains of the ionic electroactive polymer laminate becomes possible. Moreover, the technique allows the determination of the position of the neutral layer of bending that is an important requirement for the calculation of the second area and bending moments of the beam. The four examples presented demonstrate the potential variations of the bending schemes, in cases where the neutral layer is at the centroid and shifted away from the centroid.