Kazuo Onishi

The effects of counter ions on characterization and performance of a solid polymer electrolyte actuator

Abstract A perfluorocarboxylic acid membrane was chemically plated with gold bends under electric stimuli in water. When exchanged with alkali metal ions as counter ions, the displacement is rapid, though charge-specific displacement, or ‘pumping’ efficiency, is small. The fast response is thought to be linked with the small radius of the hydrated ion relative to the hydrophilic channel size in the membrane. In contrast, the charge-specific displacement with alkyl ammonium ions increases, while the rate decreases, systematically with molecular size. The effects are interpreted in terms of an ‘ion-pumping’ model, in which the size of the hydrated ion relative to that of the hydrophilic channel is of paramount importance. A good ‘pumping’ ion inevitably effects only a slow displacement.

State of water and ionic conductivity of solid polymer electrolyte membranes in relation to polymer actuators

This paper studies the state of the water and the ionic conductivity of solid polymer electrolyte membranes (SPM) of various ionic forms relating to polymer actuators. Perfluorinated polymers in both sulfonic and carboxylic forms were studied. From differential scanning calorimetry (DSC) measurements, the freezable water content in the SPM was estimated. From impedance measurements, the membrane conductivity of the SPM was estimated by equivalent circuit analysis. The counter cation in the SPM can be categorized in three groups from the freezable water content and the ionic conductivity of the membrane. Group A includes small hydrophilic cations such as those of the alkali and alkaline earth metals, for which the membrane conductivity increases with an increase in the freezable water content of the membrane. Group B includes hydrophobic cations such as alkyl ammonium ions except tetrapropyl- and tetrabutyl-ammonium ions in the perfluorosulfonic acid membrane. The ionic conductivity depends on the size of the ion and the membrane has a relatively large freezable water content. Group C includes the large hydrophobic cations such as TPrA and TBA in perfluorosulfonic acid membrane, which have a low conductivity and low freezable water content. In the light of these results, the deformation properties of the SPM/metal composites are discussed.

Polymer actuator driven by ion current at low voltage, applied to catheter system

There is considerable present interest in developing mechanochemical materials which use the swelling of ion exchange membranes technologies suitable for the construction of electromechanical actuators of very small dimensions. Both sides of a film of perfluorocarboxylic acid were chemically plated with gold. A pulse voltage of 2.0 V between the gold electrodes on the polymer ribbon gave a quick bend 90 degree angle, 8 mm displacement toward the anode side of the ribbon in water. The displacement performance of this composite is five times larger than that of Nafion-Pt composite. This report describes in detail the remarkably large bending motion polymer-micro-actuator using perfluorocarboxylic acid film and gold plate composite.

Polymer electrolyte actuator with gold electrodes

A perfluorinated cation-exchange membrane plated with noble metals was found to bend with electric stimuli in water or a saline solution. The bent to anode is almost proportional to the applied voltage around 1.5 V, which is low enough to avoid electrolysis of water. The response is as quick as muscle. Composite of perfluorocarboxylic acid and electrodes gave larger displacement than that of perfluorosulfonic acid. Gold electrodes were deposited on the polymer electrolyte with large surface area by repeated plating, and showed larger displacement without gas evolution than platinum electrodes. Alkyl ammonium cation in the composite gave slower but larger displacement than alkali metal cations. The displacement of the strip of actuator in typical dimension of 0.2 mm thick and 10 mm long is more than 5 mm without gas evolution. A tubular actuator with four electrodes was fabricated with the newly developed components and bent more than 90 degree in 2 cm length to all directions.

Bending response of polymer electrolyte actuator

To induce bending motion in a perfluorinated polymer electrolyte by electric stimuli in water or saline solution, plating with metal is required. To fabricate electrodes, a perfluorocarboxylic acid membrane was soaked in Au(III) di- chloro phenanthroline complex solution, and then any adsorbed Au(III) cation complex was reduced in aqueous sodium sulfite. Optimizing the motion response depends on control of the chemical plating procedure. By sequential adsorption/reduction cycling, a suitable pair of gold electrodes with a fractal-like structure have been grown. We illustrate the advantage of optimizing the interfacial area between electrode and membrane to enhance deformation response. To achieve this, gold deposits in the film are accumulated by sequential adsorption/reduction plating cycles. Actuator displacement increased with the number of plating gold deposition cycles up to roughly 6 times, but showed no clear improvement beyond. It is believed that with excessive plating, the interfacial area begins to decrease and/or the hardness of the electrode increases, thus countering any improvement in electrical conductance. Displacement rates were proportional to current. This high interfacial area between the electrodes and polymer electrolyte leads to larger deformation. The measured deformation progressively improves with cycling. Its motional response and versatility are illustrated by some examples.

Biomimetic microactuators based on polymer electrolyte/gold composite driven by low voltage

This paper reports a method to make a biomimetic microactuator having large displacement and uniquely controllable motion. It is based on a polymer electrolyte membrane/gold composite in which the identity of the cation influences its motional response to stimulus. The gold electrode is fractal-like with exceptionally high interfacial area. Its motional response and versatility are illustrated by several examples. Using various connection schemes, complex and life-like modes of behavior can be simulated.

State of water and transport properties of solid polymer electrolyte membranes in relation to polymer actuators

This paper studies the state of the water and the ionic conductivity of solid polymer electrolyte membranes (SPM) in relation to polymer actuators. The ionic conductivity was evaluated by impedance measurements and the specification of water in the SPM, such as total water, freezable water, non- freezable water, was carried out by DSC measurements. Dependency on the type of fixed charge of perfluorinated polymers and the couter ion was studied. The effect of the heat-treatment of the SPM was also studied. These properties were discussed in relation to the performance of the actuation of the composite composed of the SPM and gold on the basis of the proposed response model and the microscopic structure of the SPM.

Vortex Control by an Artificial Muscle Based on the Conducting Polymer

We have proposed the flow control by using an artificial muscle based on the conducting polymer. In order to utilize the artificial muscle for flow control, it is important to clarify the mechanical properties on the artificial muscle based on the conducting polymer. The purpose of this study is to clarify the mechanical properties on artificial muscle and possibility of flow control by using it. We have measured the tensile force generated by artificial muscle in the distilled water. Moreover, we have observed the actuation of artificial muscle based on the conducting polymer in water tunnel. The tensile force of artificial muscle increased as the electrode potential increased. The averaged maximum tensile force did not depend on the scan rate of electrode potential. It depended on the electrode potential and was almost constant. However, the time for reaching maximum tensile force depended on the scan rate. The artificial muscle performed the bending actuation sufficiently not only static water but also running water. Therefore, it can be considered that the artificial muscle will be applied to the actuator for flow control.© 2003 ASME