Low-voltage electroactive polymer (EAP) actuators have great potential for a variety of practical applications, [1] if they are operable in air quickly over a long period of time with a large movement under ambient conditions. While ordinary EAP actuators work only in electrolyte solutions, Wallace and coworkers reported in 2003 'dry' EAP actuators that work in air, using ionic liquids as 'built-in' electrolytes.[2] However, in principle, such conductive polymer-based actuators have an essential drawback in their lifetime and responsivity, because the motion is Faradaically driven via oxidation/reduction of the conjugated polymers. Meanwhile, Baughman and coworkers took notice of single-walled carbon nanotubes (SWNTs) as the active material, for their superb conductivity, [3] surface width, [4] and mechanical strength, [5] and fabricated novel actuators using nanotube sheets obtainable from an aqueous SWNT dispersion, [6a] or nanotube fibers processed by dry spinning from SWNT forests produced by a chemical vapor deposition (CVD) method.[6b] These actuators are unique in that they are nonFaradaically driven via electrical charge/discharge of SWNTs. However, the actuation occurs only in electrolyte solutions. Recently, we developed a 'dry' actuator composed of highpressure CO conversion (HiPco)-SWNTs and an ionic liquid, [7] based on our discovery that, upon being ground in ionic liquids, SWNTs form gelatinous materials, that is, 'bucky gels'. [8] Analogous to Baughman's examples, [6] this actuator works nonFaradaically. The actuator strip, which is structurally supported by a fluorinated polymer, adopts a bimorph configuration, in which gelatinous SWNT/ionic-liquid electrode layers laminate an ionicliquid electrolyte layer. Noteworthy, the actuator can move in air for a long time with a small battery. However, the performance is forced to compromise, since the supporting polymer, essential for the actuator strip to possess a sufficient mechanical robustness, lowers the electrical conductivity and capacitance of the electrode layers. Here, we report a second-generation SWNT actuator composed of polymer-free nanotube electrodes, which shows a much better performance than previously reported 'dry' EAP actuators, including our first-generation design. This achievement was possible due to our interesting finding that millimeterlong 'super-growth' carbon nanotubes (SG-SWNTs), [9] produced by a water-assisted modified CVD method, associate together tightly with ionic liquids, affording a free-standing sheet with superb conductivity.As a typical example for the fabrication of the SG-SWNTsheets, a suspension of SG-SWNTs (15 mg) in dimethylacetamide (DMAc, 3 mL) containing 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI, 15 mg) was sonicated for 5 min using a horn-type ultrasonic probe (a Nissei model US-50 ultrasonic generator, 28 kHz, 50 W), whereupon it turned to a gel (Fig. 1a). The gelatinous material, thus obtained, was diluted with DMAc (6 mL), and then an aliquot (2.4 mL) was cast on a Te...
