Shigeki Tsuchitani

Nafion®-based polymer actuators with ionic liquids as solvent incorporated at room temperature

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.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-imid...

Humidity dependence of microwear characteristics of amorphous carbon films on silicon substrates

Abstract Influences of environmental humidity on various scanning-scratched wear characteristics, such as long-term stability of wear resistance and load dependence, scratch number dependence and scratch velocity dependence of wear depth, are evaluated by using an atomic force microscope and diamond tips. Amorphous carbon (a-C) films are deposited on silicon substrates by the electron cyclotron resonance plasma (ECR) sputtering method and the RF sputtering method combined with CVD using argon gas containing methane (CH 4 ) as a sputtering gas. In carbon samples with a higher hydrogen content, clear influences of the humidity on various wear characteristics are observed and their wear resistances decrease with increase of the humidity. In the ECR sputtered carbon film with low hydrogen content, wear resistance is stable during long-term exposure to an environment of high temperature and high humidity. In this film, the influences of humidity on the wear resistance and adhesion forces between the films and the substrates are not observed, since it is highly wear resistant and the wear depths are shallow in each test. Thus, amorphous carbon films with low hydrogen content are suitable as wear resistant protective overcoats from the point of view of the wear resistance, in particular the influence of the humidity on the wear resistance including its long-term stability.

Ultrathin amorphous carbon overcoats by filtered cathodic arc deposition

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/sup 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.

Comparative study of bending characteristics of ionic polymer actuators containing ionic liquids for modeling actuation

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 a...

Nanometer-Scale Recording on a Superhard and Conductive Carbon Film Using an Atomic Force Microscope

Nanometer-scale recording on a carbon film deposited by electron cyclotron resonance plasma sputtering (ECR-C) is demonstrated by locally changing the electrical resistance using an atomic force microscope. The recording mechanism is thermal annealing of the film surface due to Joule heat generated by the probe current. Such a recording without apparent topographic changes is considered to be possible due to the higher electrical conductivity of the ECR-C than those of conventional amorphous carbons. Namely, it enables us to modify the surface at a lower application voltage than the voltage above which topographic changes due to field-induced oxidation occur. High-density probe storage is demonstrated by applying pulse voltage rows to the ECR-C. The minimum size of the data bit is about 70 nm.

Dielectric elastomer actuators using Slide-Ring Material® with increased permittivity

The inclusion of high permittivity nanoparticles in elastomeric materials for dielectric elastomer actuators (DEAs) is one promising method to achieve large strain at relatively low applied voltages. However, the addition of these nanoparticles tends to increase the stiffness of the elastomer and disturbs the actuation of the DEA. This is attributed to restriction of the chain motion in the elastomer by the nanoparticles. Slide-Ring Material® (SRM) is a cross-linked polymeric material with freely movable cross-linking sites. The internal stresses in this structure are dramatically homogenized by the pulley effect; therefore, the restriction of chain motion due to the nanoparticles is expected to be significantly reduced. We have employed SRM as a host elastomer for a DEA with the addition of ferroelectric BaTiO3 (BT) nanoparticles. The effects of BT addition on the permittivity, stiffness and viscosity of the SRM–BT nanocomposites, and the actuation strain of DEAs using SRM were evaluated. The permittivity of the nanocomposites increased linearly with the concentration of BT and reached 3.6 times that for pure SRM at 50 wt%. The elastic modulus and the viscosity remained almost constant up to 20 wt% and then decreased above this concentration. The actuation strain of a planar actuator using SRM and 50 wt% BT was four times larger than that of the DEA with pure SRM.

Annealing-Induced Modification of Superhard Conductive Carbon Film

Carbon deposited by electron cyclotron resonance plasma sputtering (ECR-C) is known to have physical properties different from those of amorphous carbon (a-C), i.e., an unexpected high degree of hardness, despite the large proportion of sp2 bonding. We studied the effects of annealing (up to 700 °C) ECR-C films on the microstructure and electrical conductive property by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and conducting atomic force microscopy (AFM). Annealing causes the evaporation of argon atoms (7.4 at. %) in the film and decreases the sp3/sp2 ratio from 0.31 to 0.24, the full width half maximums (FWHMs) of G and D peaks and the I(D)/I(G) ratio. The electrical conductivity and linearity of I–V curves measured by conducting AFM increase with annealing temperature. This is explained by the ordering of the sp2 phase, i.e., the decrease in the numbers of argon atoms and defects in aromatic rings, which act as ionizable sites for Poole–Frenkel conduction. The variations in FWHM, I(D)/I(G) ratio and electrical conductivity are much smaller than those caused by annealing a-C with an sp3 fraction lower than approximately 70%. This indicates that ECR-C is thermally stable compared with a-C, i.e., the basic structure of ECR-C is maintained during annealing up to 700 °C with a small increase in the size of sp2 nanocrystallites and a lowering of disorder.

Evaluation of a Lightly Scratched Amorphous Carbon Surface by Contact Resistance of a Conductive Diamond Tip and the Carbon Surface

An electron-cyclotron-resonance-sputtered amorphous carbon film is scratch-scanned by an AFM and a conductive diamond tip at small contact loads (≤2μN). The electrical contact resistance between the tip and the scratched carbon surface increases upon increasing the scratching load and the number of scratching scans and decreases with increasing scratching velocity. The wear depth is less than 0.6 nm in all scratching experiments and is almost independent of the scratching load, the number of scratching scans and the scratching velocity. The change in contact resistance caused by the scratching is affected by environmental humidity. The magnitude of the change in the contact resistance is almost the same at 20 and 50% RH and increases with increasing relative humidity at humidities higher than 50% RH. The contact resistance also increases upon scratching in vacuum. The change in contact resistance is thought to be caused by tribochemical oxidation of the rubbed surface by humid air and also destruction of the graphite structure of the ECR-sputtered carbon surface.

Fabrication of microstructure array directly on β-phase poly(vinylidene fluoride) thin film by O2 reactive ion etching

The ability to pattern a thin film of poly(vinylidene fluoride) (PVDF), a piezoelectric, pyroelectric and ferroelectric polymer, has potential applications in the fields of microelectromechanical systems (MEMS), nonlinear optics and nonvolatile ferroelectric random access memory technology. Low pressure O2 reactive ion etching (RIE) was employed to realize fine pitch microstructures on a β-phase PVDF (β-PVDF) film for the first time; a line and space (70/130 μm) microstructure array with a height of over 30 μm was fabricated. Different to the traditional method of PDMS molding, the proposed technology did not result in significant loss of piezoelectricity. Furthermore, unlike the x-ray photo-etching method, there was no etching saturation limit with the proposed method. Here, we introduce the fabrication process technology in detail and report on the etching properties of the β-PVDF film under different process conditions. The effect of process variables, such as supplied gas flow, applied RF power and etch time, on the PVDF etching characteristics were investigated in detail. The RF power and etch time showed a more predominant influence on PVDF etching progress than the gas flow. The etched depth was linearly increased with the etch time and the amount of RF power. Etching rates over 10 μm h−1 were achieved and increased linearly with the applied RF power. By means of a responding photomask design and control of process conditions, much finer and higher microstructure arrays are also possible.

Chemical Propulsion Using Ionic Liquids

Chemical propulsion generates motion by directly converting locally stored chemical energy into mechanical energy. Here, we describe chemically driven autonomous motion generated by using imidazolium-based ionic liquids on a water surface. From measurements of the driving force of a locomotor loaded with an ionic liquid and observations of convection on the water surface originating from the ionic liquid container of the locomotor, the driving mechanism of the motion is found to be due to the Marangoni effect that arises from the anisotropic distribution of ionic liquids on the water surface. The maximum driving force and the force-generation duration are determined by the surface activity of the ionic liquid and the solubility of the ionic liquid in water, respectively. Because of the special properties of ionic liquids, a chemical locomotor driven by ionic liquids is promising for realizing autonomous micromachines and nanomachines that are safe and environmentally friendly.