High-Performance PEDOT:PSS/Single-Walled Carbon Nanotube/Ionic Liquid Actuators Combining Electrostatic Double-Layer and Faradaic Capacitors

New hybrid-type poly­(3,4-ethylenedioxythiophene) (PEDOT) actuators produced by the film-casting method, in which both electrostatic double-layer (EDLC) and faradaic capacitors (FCs) occur simultaneously, have been developed. The electrochemical and electromechanical properties of PEDOT:poly­(4-styrenesulfonate) (PSS), PEDOT:PSS/ionic liquid (IL), and PEDOT:PSS/single-walled carbon nanotubes (SWCNTs)/IL actuators are compared with those of a conventional poly­(vinylidene fluoride)-<i>co</i>-hexafluoropropylene (PVdF­(HFP))/SWCNT/IL actuator. It is found that the PEDOT:PSS/SWCNT/IL actuator provides a better actuation strain performance than a conventional (PVdF­(HFP))/SWCNT/IL actuator, as its electrode is an electrochemical capacitor (EC) composed of an EDLC and FC. The PEDOT:PSS polymer helps produce a high specific capacitance, actuation strain, and maximum generated stress that surpass the performance of a conventional PVdF­(HFP) actuator. The flexible and robust films created by the synergistic combination of PEDOT and SWCNT may therefore have significant potential as actuator materials for wearable energy-conversion devices. A double-layer charging kinetic model was successfully used to simulate the frequency dependence of the displacement responses of the PEDOT:PSS/IL and PEDOT:PSS/SWCNT/IL actuators

High-Performance Hybrid (Electrostatic Double-Layer and Faradaic Capacitor-Based) Polymer Actuators Incorporating Nickel Oxide and Vapor-Grown Carbon Nanofibers

The electrochemical and electromechanical properties of polymeric actuators prepared using nickel peroxide hydrate (NiO2·xH2O) or nickel peroxide anhydride (NiO2)/vapor-grown carbon nanofibers (VGCF)/ionic liquid (IL) electrodes were compared with actuators prepared using solely VGCFs or single-walled carbon nanotubes (SWCNTs) and an IL. The electrode in these actuator systems is equivalent to an electrochemical capacitor (EC) exhibiting both electrostatic double-layer capacitor (EDLC)- and faradaic capacitor (FC)-like behaviors. The capacitance of the metal oxide (NiO2·xH2O or NiO2)/VGCF/IL electrode is primarily attributable to the EDLC mechanism such that, at low frequencies, the strains exhibited by the NiO2·xH2O/VGCF/IL and NiO2/VGCF/IL actuators primarily result from the FC mechanism. The VGCFs in the NiO2·xH2O/VGCF/IL and NiO2/VGCF/IL actuators strengthen the EDLC mechanism and increase the electroconductivity of the devices. The mechanism underlying the functioning of the NiO2·xH2O/VGCF/IL actuator in which NiO2·xH2O/VGCF = 1.0 was found to be different from that of the devices produced using solely VGCFs or SWCNTs, which exhibited only the EDLC mechanism. In addition, it was found that both NiO2 and VGCFs are essential with regard to producing actuators that are capable of exhibiting strain levels greater than those of SWCNT-based polymer actuators and are thus suitable for practical applications. Furthermore, the frequency dependence of the displacement responses of the NiO2·xH2O/VGCF and NiO2/VGCF polymer actuators were successfully simulated using a double-layer charging kinetic model. This model, which accounted for the oxidization and reduction reactions of the metal oxide, can also be applied to SWCNT-based actuators. The results of electromechanical response simulations for the NiO2·xH2O/VGCF and NiO2/VGCF actuators predicted the strains at low frequencies as well as the time constants of the devices, confirming that the model is applicable not only to EDLC-based actuator systems but also to the fabricated EDLC/FC system

Actuation and blocking force of stacked nanocarbon polymer actuators

We have developed stacked nanocarbon polymer actuators that are composed of several nanocarbon polymer actuator films using nonwoven fabric as insulation layers. The nonwoven fabric prepared through electrospinning methods has extremely-low-density structures, which do not significantly prevent the motions of each nanocarbon actuator layer. Therefore, stacking several thin nanocarbon polymer actuators using nonwoven fabric as insulation layers is expected to increase generated force without decreasing the displacement of a one-layer actuator. We have prepared stacked actuators with one, two, three, four, and seven layers using this method. The displacement and blocking force of these actuators are measured and compared with those of one-layer actuators of different thicknesses. Displacement is weakly dependent on the thickness of the actuator films of the stacked actuators. On the contrary, it decreases considerably as the thickness of the actuator film of the one-layer actuator increases. In both cases, blocking force is proportional to the thickness of actuator films. We have developed a stacked actuator model based on a trilayer actuator model and confirmed the experimental results using the model.</p

Relationship between Mechanical and Electrical Properties of Continuous Polymer-Free Carbon Nanotube Fibers by Wet-Spinning Method and Nanotube-Length Estimated by Far-Infrared Spectroscopy

Neat carbon nanotube (CNT) fibers produced by wet spinning methods offers a potential for high-strength and electrically conductive lightweight materials. For improving their performances, it is necessary to understand how each manufacturing process affects the raw CNTs and implicates the effects in the fiber properties. Recently, we found that the lengths of the clean CNT channels can be estimated by far-infrared (FIR) spectroscopy based on the plasmon resonance model. In this paper, the relationship between the mechanical properties and electric conductivities of the neat CNT fibers, and the lengths of the constituent CNTs are systematically studied by using different types of single-walled CNTs (SWCNTs) with various diameters and different dispersing times. Irrespective of the type of CNTs or the tube diameters, Young moduli, fracture strengths, and electric conductivities of the CNT fibers were found to be related to the CNT lengths estimated from the FIR spectra. The results prove that the evaluation of CNT length by the FIR spectroscopy is a highly useful method to optimize the processing conditions as well as to select the proper CNTs for fabricating high-performance CNT-based materials

Medium Effects on the Nucleation and Growth Mechanisms during the Redox Switching Dynamics of Conducting Polymers: Case of Poly(3,4-ethylenedioxythiophene)

The redox switching dynamics of poly(3,4-ethylenedioxythiophene) (PEDOT) in an acetonitrile solution and a room temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmiTFSI), are investigated by means of potential step experiments. Redox switching can be viewed as a phase transition in which the nucleation and growth processes occur. We have developed a phenomenological model allowing the determination of the kinetic parameters. Two limiting cases are shown as follows: (i) a progressive and (ii) an instantaneous nucleation. In all cases, the growth process is described in terms of a self-exchange electron transfer reaction. We show that the mechanisms depend upon the medium. In acetonitrile, progressive nucleation and growth occur during oxidation (p-doping), whereas nucleation is instantaneous in the reduction of the PEDOT film. On the other hand, instantaneous nucleation and growth mechanisms are observed for both oxidation and reduction in EmiTFSI. The difference in the mechanisms results from the ionic exchange process associated with electron transfer and the initial structure of the film (open or compact). The influence of the applied potential on the dynamics is analyzed for both media