Kunitomo Kikuchi

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...

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...

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.

Development of an active micro catheter using a conducting polymer actuator and silicone tube

In this paper, we proposed a structure of an active catheter using polypyrrole (PPy). PPy is one of conducting polymer actuators that are suitable for microactuator for medical use. We fabricated an active catheter of two actuator type which was coated with an electrolyte gel. It was driven in air, and a radius of curvature of 146mm was obtained. In order to enlarge the bending displacement of the catheter, we used thin metal films as electrode for polymerization of PPy. A trimorph actuator with an Au electrode and an electrolyte gel to drive PPy in air, exhibited 6.4 times larger curvature than that using a conducting polymer as electrode. We simulated the operation of the active catheter with the Au electrode to optimize various sizes by a finite element analysis.

Evaluation of basic operating characteristics of ion conductive polymer actuator using ionic liquid

Nafionreg-based ionic polymer-metal composites (IPMCs), whose counter ions are exchanged using ionic liquids, are fabricated. EMIBF4, BMIBF4, and BMIPF6 are used as ionic liquids. During long-term (180 min.) operation in air, changes in curvature of IPMCs are about 10% of the initial one. This change is enough smaller than that of conventional IPMCs using metallic counter ion. The curvature is larger in IPMC having lower charge transfer resistance, which is evaluated measuring frequency dependent complex impedance of IPMC. Furthermore, charge transfer resistance of IPMC decreases with increase in environmental humidity.

Fabrication of ionic polymer-metal actuator of microcantilever type

In this study, in order to develop fabrication process of ionic polymer-metal composite (IPMC) actuator of microcantilever type, we evaluated actuation characteristics of a thin film type IPMC. Though its displacement was smaller than that of IPMCs fabricated by using the commercial ionic polymer (Nafion) film, the actuation of the thin film type IPMCs was confirmed. It depended on the thickness of the Nafion layer. We can expect the realization of MEMS devices integrated with the thin film type micro IPMCs fabricated by the propose method.

Development of flexible rubber electrode for dielectric elastomer actuator

Dielectric elastomer actuator (DEA) is expected as an artificial muscle. In this study, fabrication methods of two types of rubber electrodes for DEA were proposed. Moreover, effect of rubber materials on rubber electrodes, effect of amount of solvent (heptane) in rubber materials on performance of DEA, and effect of conducting materials (Ketjen Black and multi wall carbon nanotube) on rubber electrodes were evaluated. The activated relative area strain increased with increase in the hardness of the rubber. The maximum area strain was 38.28% when 4kV was applied. On the other hand, the fabrication method using low solvent has a possibility to fabricate DEA efficiently.

Unstable Spreading of Ionic Liquids on an Aqueous Substrate

The spontaneous spreading of thin liquid films over substrate surfaces is attracting much attention due to its broad applications. Under particular conditions, surfactants deposited on substrates exhibit unstable spreading. In spite of the large effects of the stability of the spreading on the accuracy and efficiency of industrial processes that use the spreading, understanding how the stability of the spreading process is governed by the physical and chemical properties of the system is still little known. Recently, ionic liquids have been characterized as a new kind of surfactant due to their special properties. Here, we investigate the stability of the spreading of deposited imidazolium-based ionic liquids on an aqueous substrate. We focus mainly on the effects that the water solubility of the ionic liquids has on the stability. Hydrophobic ionic liquids exhibit spreading that has a highly periodic and petal-like unstable spreading front, whereas hydrophilic ionic liquids spread without such a regular spreading front and their spreading area shrinks after reaching its maximum. We propose a model for the generation of unstable spreading of hydrophobic ionic liquids, i.e., the unstable spreading front is created by the penetration of oncoming water in front of the spreading tip into the more viscous spreading ionic liquid layer, like the viscous fingering that occurs in a Hele-Shaw cell. However, the direction of the penetration is the opposite of the direction that the interface moves (the spreading direction), which is contrary to that in viscous fingering.

Study of the Influence of the Hydration Level on the Electromechanical Behavior of Nafion Based Ionomeric Polymer-metal Composites Actuators

The ionomeric electroactive polymers-metal composites (IPMC) are materials that realize bending movements in response to an electrical stimulus and can be applied to the artificial muscles development. This paper investigated the influence of the hydration level on the electromechanical behavior of Nafion based IPMC. An experimental apparatus composed by a system to measure the bending force and to control the electrical stimulus and the relative humidity around the sample was developed. The main results indicated that samples with higher hydration level produce larger bending forces, but they show a more expressive back relaxation with lower time constant. A discussion about the results considering some models described in the literature conclude the paper.

Ionic Conductive Polymers

Electro active polymers (EAPs) are attracting considerable interest due to their special characteristics, including high flexibility and low weight. Ionic conductive polymers have the potential to play a main role in the realization of smart systems for applications such as bio inspired and autonomous robotics, medical devices, and aerospace. Ionic polymer-metal composites (IPMCs) are one of the most promising EAP materials for the artificial muscle-like actuators and sensors. Typical applications of IPMC are soft robotic actuators, since they are suitable for micro actuators in devices used in the human body due to their flexibility and good biological compatibility. In this chapter, the fundamental aspects of the IPMC, i.e., typical fabrication methods, evaluation techniques for testing, recent results of fabrication of miniaturized IPMC, and recent developments of materials of ion conductive polymer actuators are described.