Driving Mechanisms of Ionic Polymer Actuators Having Electric Double Layer Capacitor Structures

Abstract

Two solid polymer electrolytes, composed of a polyether-segmented polyurethaneurea (PEUU) and either a lithium salt (lithium bis(trifluoromethanesulfonyl)amide: Li[NTf2]) or a nonvolatile ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide: [C2mim][NTf2]), were prepared in order to utilize them as ionic polymer actuators. These salts were preferentially dissolved in the polyether phases. The ionic transport mechanism of the polyethers was discussed in terms of the diffusion coefficients and ionic transference numbers of the incorporated ions, which were estimated by means of pulsed-field gradient spin-echo (PGSE) NMR. There was a distinct difference in the ionic transport properties of each polymer electrolyte owing to the difference in the magnitude of interactions between the cations and the polyether. The anionic diffusion coefficient was much faster than that of the cation in the polyether/Li[NTf2] electrolyte, whereas the cation diffused faster than the anion in the polyether/[C2mim][NTf2] electrolyte. Ionic polymer actuators, which have a solid-state electric-double-layer-capacitor (EDLC) structure, were prepared using these polymer electrolyte membranes and ubiquitous carbon materials such as activated carbon and acetylene black. On the basis of the difference in the motional direction of each actuator against applied voltages, a simple model of the actuation mechanisms was proposed by taking the difference in ionic transport properties into consideration. This model discriminated the behavior of the actuators in terms of the products of transference numbers and ionic volumes. The experimentally observed behavior of the actuators was successfully explained by this model.

Fast low-voltage electroactive actuators using nanostructured polymer electrolytes

“…As the electromechanical motion in ionic polymer actuators occurs through the migration of ions towards oppositely charged electrodes upon the application of an electric field 8,9 , ion transport properties and electrochemical stability of polymer electrolytes have important roles in determining the performance of the actuators 10,11 . Conventional polymers that appear to be leading candidates for the actuators include poly(vinylidene fluoride) (PVdF)-based polymers [12][13][14][15] , conjugated polymers 16,17 and perfluorinated ionomers with random inclusions of acidic moieties (that is, Nafion) [18][19][20] .…”

“…In fact, research on actuators comprising ionic liquids has commonly used a few conventional polymers 25,26 , thus impeding major advances in ionic polymer actuators, which essentially require the optimization of ion transport characteristics and mechanical properties of the polymer layer. In this respect, the use of microphase-separated polymers in actuators has recently been proposed as a promising means to elevate the actuator performance 7,10,[33][34][35][36][37][38][39][40][41] . For instance, Long et al 34,35 , Spontak et al 7,36,37 , Colby et al 38,39 and Watanabe et al 10,40 , have employed self-assembled block copolymers in actuators and improved electromechanical deformation has been reported, compared with that of several conventional polymers lacking organization.…”

Design and Materialization of Ionic Liquids Based on an Understanding of Their Fundamental Properties

“…33 Herein, I discuss the application of an ion gel to ionic polymer actuators. [38][39][40][41][42] As a material for manufacturing polymer actuators with bio-mimetic soft motion, electronic and ionic polymer actuators have been proposed and applied to manipulators and robotic devices. Ionic polymer actuators driven by migration or diffusion of ions can achieve relatively large deformations in response to the application of low voltages.…”

“…The deformation mechanism is interpreted regarding the differences in cationic and anionic mobilities (transference number) and sizes. 40,41 Such differences induce a volume imbalance between the cathode and anode, resulting in a bending motion of the actuators.…”

Effects of Carbon Electrode Materials on Performance of Ionic Polymer Actuators Having Electric Double-Layer Capacitor Structure

“…Electroactive polymer (EAP) actuators, 14 such as conducting polymer, 2,3 ionomeric polymer-metal composite, 4 and dielectric elastomer actuators, 5 can be driven by transducing electric energy into mechanical motion. In the past decade, EAP actuators, which transform their shape responding to electric stimulus, have been expected to be applied to artificial muscles, robots, speakers, micropump, manipulator, and so on, because they have soft motion and light weight compared with other types of actuators.…”