Nafion®-based ionic polymer-metal composites (IPMCs), with ionic liquids as solvent, were fabricated by exchanging counterions to ionic liquids at room temperature. Ion exchange is performed by only immersing IPMC in a mixture of de-ionized water and ionic liquids at room temperature for 48 h. The fabricated IPMCs exhibited a bending curvature the same as or larger than that of conventional IPMCs with ionic liquids, formed by ion exchange to ionic liquids at an elevated temperature up to about 100 °C, and also had long-term stability in operation in air, with a fluctuation smaller than 21% in bending curvature during a 180 min operation. The effective ion exchange to ionic liquids in the present method is probably due to an increase in diffusion speed of ionic liquids into IPMC by adsorption of water in a Nafion® membrane. It is a surprise that among IPMCs with ionic liquids 1-ethyl-3-methyl-imidazolium tetrafluoroborate, 1-buthyl-3-methyl-imidazolium tetrafluoroborate (BMIBF4), and 1-buthyl-3-methyl-imidazolium hexafluorophosphate (BMIPF6), IPMC with water-insoluble BMIPF6 exhibited a larger bending curvature than that IPMC with water-miscible BMIBF4. This might be due to effective incorporation of BMIPF6 into IPMC, since BMIPF6 has a higher affinity with IPMC than with water in the mixture of water and BMIPF6. From measurements of complex impedance and step voltage response of the driving current of IPMCs with ionic liquid, they are expressed by an equivalent circuit of a parallel combination of a serial circuit of membrane resistance of Nafion® and electric double layer capacitance at metal electrodes, with membrane capacitance of Nafion®, in a frequency range higher than about 0.1 Hz. The difference in magnitude of bending curvature in three kinds of IPMCs with ionic liquids is mainly due to the difference in bending response speed coming from the difference in the membrane resistance.
We report a method of fabricating microstructures directly on a thin β-phase polyvinylidene fluoride (PVDF) film without losing much of its piezoelectricity by employing wet and dry etching technologies. The piezoelectricity of PVDF depends greatly on the temperature, as is generally known. The process conditions, including the PVDF temperature history, were evaluated in experiments where there was almost no change in the PVDF film piezoelectric constant below 60 • C per 4 h. The constant of d 33 in the range above 60 • C per 4 h linearly deteriorated with the rise in temperature by 0.3 × 10 −12 (C N −1 ) • C −1 and at a temperature of 100 • C per 4 h; deterioration of about 50% was confirmed. The N,N -dimethyl acetamide (DMA: C 4 H 9 NO) solution was used as the etchant for wet etching, and O 2 plasma was used for the reactive ion etching (RIE). Tens to a hundred micrometer microstructures were easily fabricated with the proposed approach. The fabrication process technology and experimental results are also reported in detail.
Ionic polymer metal composites (IPMCs) that can operate in air have recently been developed by incorporating an ionic liquid in ionic polymers. To understand transduction in these composites, it is important to determine the role of the ionic liquid in the ionic polymer (Nafion®), to identify the counter cation, and to investigate the interaction of IPMCs with water vapor in the air. We used Fourier-transform infrared spectroscopy to analyze three Nafion® membranes, which were soaked in mixtures of water and an ionic liquid (1-ethyl-3-methyl-imidazolium tetrafluoroborate (EMIBF4), 1-buthyl-3-methyl-imidazolium tetrafluoroborate (BMIBF4), and 1-buthyl-3-methyl-imidazolium hexafluorophosphate (BMIPF6)). The results demonstrate that only cations (EMI+ and BMI+) in the ionic liquids are taken into the Nafion® membranes as counter ions and that the water content of the membranes in air is less than ∼4% that of Nafion® swollen with water. Based on the experimental results, a transduction model is proposed for an IPMC with an ionic liquid. In this model, bending is caused by local swelling due to the volume effect of the bulky counter cations. This model can explain 30–50% of the experimentally observed bending curvature.
We studied properties of 2-to 25-nm-thick tetrahedral amorphous carbon films produced by filtered cathodic arc deposition. We found that nitrogen doping was effective in controlling film properties. Both the amount of sp 3 bonding in the film and the hardness decreased with nitrogen incorporation. The adhesion of lubricant to the carbon film was improved by nitrogen doping. Tests of wear and corrosion on a nanometer scale showed the superior tribological and anticorrosion performance of tetrahedral amorphous carbon films over hydrogenated amorphous carbon films.
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