Satoru Imaizumi

High-performance ion gel with tetra-PEG network

In this paper, we show a free-standing highly ion-conducting ionic liquid (IL)-polymer electrolyte, Tetra-PEG ion gel, prepared by incorporating imidazolium-based ILs into very much lower concentration (3–6 wt%) of tetra-arm poly(ethylene glycol), Tetra-PEG. The ionic conductivities of the free-standing Tetra-PEG ion gels were nearly equal to those of pure ILs, indicating a realization of liquid-like conductivity in a solid-state material. The Tetra-PEG ion gels showed advanced mechanical properties demonstrated by the results of compression and stretching tests.

Driving mechanisms of ionic polymer actuators having electric double layer capacitor structures

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.

Printable Polymer Actuators from Ionic Liquid, Soluble Polyimide, and Ubiquitous Carbon Materials

We present here printable high-performance polymer actuators comprising ionic liquid (IL), soluble polyimide, and ubiquitous carbon materials. Polymer electrolytes with high ionic conductivity and reliable mechanical strength are required for high-performance polymer actuators. The developed polymer electrolytes comprised a soluble sulfonated polyimide (SPI) and IL, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C2mim][NTf2]), and they exhibited acceptable ionic conductivity up to 1 × 10(-3) S cm(-1) and favorable mechanical properties (elastic modulus >1 × 10(7) Pa). Polymer actuators based on SPI/[C2mim][NTf2] electrolytes were prepared using inexpensive activated carbon (AC) together with highly electron-conducting carbon such as acetylene black (AB), vapor grown carbon fiber (VGCF), and Ketjen black (KB). The resulting polymer actuators have a trilaminar electric double-layer capacitor structure, consisting of a polymer electrolyte layer sandwiched between carbon electrode layers. Displacement, response speed, and durability of the actuators depended on the combination of carbons. Especially the actuators with mixed AC/KB carbon electrodes exhibited relatively large displacement and high-speed response, and they kept 80% of the initial displacement even after more than 5000 cycles. The generated force of the actuators correlated with the elastic modulus of SPI/[C2mim][NTf2] electrolytes. The displacement of the actuators was proportional to the accumulated electric charge in the electrodes, regardless of carbon materials, and agreed well with the previously proposed displacement model.

Thermoreversible high-temperature gelation of an ionic liquid with poly(benzyl methacrylate-b-methyl methacrylate-b-benzyl methacrylate) triblock copolymer

In this paper, we describe a novel thermosensitive triblock copolymer in an ionic liquid (IL) that shows a low-temperature-sol–high-temperature-gel transition. A well-defined ABA triblock copolymer consisting of poly(benzyl methacrylate) as the terminal A blocks and poly(methyl methacrylate) as the middle B block (P(BnMA-b-MMA-b-BnMA), BMB) was successfully synthesized using atom transfer radical polymerization (ATRP) from a bifunctional initiator. The number-average molecular weights of the PBnMA blocks and the PMMA block were estimated to be 25 kDa and 33 kDa, respectively. The temperature dependence of the hydrodynamic radius obtained from dynamic light scattering showed that in dilute solutions (0.1 wt%) the triblock copolymer exhibited lower critical micellization temperature (LCMT)-type aggregation behaviour around 135 °C in a common hydrophobic IL, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C2mim][NTf2]). Dynamic viscoelastic measurements for a 20 wt% BMB solution in [C2mim][NTf2] confirmed that a viscous liquid at low temperature (G′ (storage elastic modulus) G′′) upon heating above the aggregation temperature of the PBnMA terminal blocks. No gelation was observed when the triblock copolymer concentration was below 10 wt%. Furthermore, the thermoreversible ion gel exhibited excellent sol–gel transition reversibility for multiple heating/cooling cycles performed over several days.

Ion Gels for Ionic Polymer Actuators

Ionic polymer actuators are driven by the migration or diffusion of ions and generally exhibit significant deformation (i.e., bending) under low-voltage (<5 V) applications. However, the durability of conventional ionic polymer actuators decreases under open atmosphere owing to the evaporation of solvents, which are essential for the movement of ions, from the actuators. In order to overcome this drawback, ionic polymer actuators that can be operated under open atmosphere and even under vacuum are being developed using ionic liquids (ILs). Combining macromolecules with ILs as additives can result in highly ion-conducting polymer electrolytes (ion gels) suitable for applications in ionic polymer actuators. However, the contribution of polymeric materials to the high performance of IL-based polymer actuators is yet to be elucidated. In this chapter, IL-based polymer electrolytes comprising block copolymers and polyimides are demonstrated to enable easily processable ionic polymer actuators with high performance and durability. The displacement response is also analyzed using our proposed displacement model.