Hirohisa Tamagawa

Influence of metal plating treatment on the electric response of Nafion

A potentially promising material as a high performance electroactive polymer gel actuator, Nafion, is known for its fast and large bending upon an applied voltage. Not long ago, it was reported that copper plating on Nafion enhances the degree of its bending. We performed the combinational metal plating treatment on Nafion surfaces with silver, copper and nickel, and the performances of metal plated Nafions—bending curvature and generated force—upon an applied voltage were quantitatively evaluated. From the obtained results, it was speculated that the hydrated mobile ions play substantial roles for the large bending of Nafion as has been widely believed and for the enhancement of its generated force. In addition to them, nickel plating on Nafion surfaces was found to enable Nafion to exhibit a large force without a significant force decay owing to the low-elastic property of nickel layers.

Enhanced contrast ratios and rapid switching color changeable devices based on poly(3,4-propylenedioxythiophene) derivative and counterelectrode

A large contrast ratio and rapid switching electrochromic(EC) polymer device which consists of laminated two-layer structure between two electrodes was proposed. The new design which only comprises an ITO coated glass electrode, a cathodic poly(3,4-propylenedioxythiophene) derivative (PProDOT-(CH3

Mechanical characteristics of ionic polymer-metal composite in the process of self-bending

2) EC polymer film, a solid electrolyte and an Au-based counterelectrode which replaces anodic EC polymer and ITO electrode. Carbon-based counterelectrode was prepared for comparing with Au-based counterelectrode. Lithography and sputtering were used for Au patterning on glass substrate, while screen printing was used for carbon-based counterelectrode. Covering percentage of Au is less than 20%, in order to keep the electrode high transmittance. We also prepared a solid electrolyte, such as poly(methyl metracrylate)(PMMA) based containing LiClO4 gel electrolyte for solid state applications. A special parafilm was utilized on sealing the assembly device. Color change of high contrast ratio of transmittance (>(Delta) 50% T) of the device is rapidly (0.5-1s) obtained upon applied 2.5V voltage and repeatable (10,000 times). The temperature range under which the switching is stable is wide, -40 degree(s)C ~ 100 degree(s)C. The repeatability of current of EC polymer devices while color change was estimated by electrochemistry.

Design of two-way reversible bending actuator based on a shape memory alloy/shape memory polymer composite

An ionic polymer-metal composite (IPMC) consisting of a thin Nafion sheet sandwiched between two thin metallic plates like platinum, silver, and copper ones exhibits a large self-bending motion in its transversal direction upon such a small voltage as 1 V. Estimating Young’s moduli and generated force, which are time dependent and difficult to measure by standard methods, is fundamental for understanding their mechanical properties. We propose a simple method to estimate the time-dependent nominal Young’s moduli and generated force in experiments. We use cantilever beams of IPMCs and obtain their Young’s moduli and generated force (bending moments) from their shapes and vertical force at the tips by neglecting their inertia and viscosity property. The validity of the method is demonstrated by numerical simulation results. For an IPMC consisting of a Nafion sheet and two thin silver plates we give experimental results, which are considerably consistent with ones previously reported. Moreover, we see that i...

Bending curvature and generated force by Nafion actuator

The design of a reversible bending actuator based on a SMA/SMP composite is presented. The SMA/SMP composite is made of SMA NiTi wires with a bent ‘U’-shape in the austenite phase embedded in an epoxy SMP matrix which has a memorized flat shape. The bending motion is caused by heating the composite above TAf to activate the NiTi recovery. Upon cooling, the softening from the austenite to R-phase transformation results in a relaxation of the composite towards its original flat shape. In the three-point bending measurement the composite was able to exhibit a reversible deflection of 1.3 mm on a support with a 10 mm span. In addition, a material model for predicting the composite’s deflection is presented and predicts the experimental results reasonably well. The model also estimates the in-plane internal force and the degree of the SMA phase transformation.

Membrane Potential Generated by Ion Adsorption

It was revealed that Cu-plated Nafion exhibits an extremely large bending upon applied voltage recently. Although this phenomenon has been thought to be owing to the continuous transport of hydrated Cu/sup 2+/ through the ionization of Cu layer on Nafion surface, we reached the conclusion that it is primarily owing to the shift of a large amount of hydrated Cu/sup 2+/ en masse, which were originally contained in Nafion body. Formation of another Ni metal layers on Nafion surfaces drastically improves the force Nafion generates. This is owing to the reinforcement of Nafion matrix. The force of Ni plated Nafion continues to increase with time upon applied voltage, although it decays without nickel plating layers. Furthermore, it was found that Nafion bending curvature was sensitive to the applied load on it. It demands a detail investigation on Nafion for the purpose of achievement a practical Nafion actuator.

Electroactive nonionic poly(vinyl alcohol) gel actuator

It has been widely acknowledged that the Goldman-Hodgkin-Katz (GHK) equation fully explains membrane potential behavior. The fundamental facet of the GHK equation lies in its consideration of permeability of membrane to ions, when the membrane serves as a separator for separating two electrolytic solutions. The GHK equation describes that: variation of membrane permeability to ion in accordance with ion species results in the variation of the membrane potential. However, nonzero potential was observed even across the impermeable membrane (or separator) separating two electrolytic solutions. It gave rise to a question concerning the validity of the GHK equation for explaining the membrane potential generation. In this work, an alternative theory was proposed. It is the adsorption theory. The adsorption theory attributes the membrane potential generation to the ion adsorption onto the membrane (or separator) surface not to the ion passage through the membrane (or separator). The computationally obtained potential behavior based on the adsorption theory was in good agreement with the experimentally observed potential whether the membrane (or separator) was permeable to ions or not. It was strongly speculated that the membrane potential origin could lie primarily in the ion adsorption on the membrane (or separator) rather than the membrane permeability to ions. It might be necessary to reconsider the origin of membrane potential which has been so far believed explicable by the GHK equation.

Generation of membrane potential beyond the conceptual range of Donnan theory and Goldman-Hodgkin-Katz equation

A fast (0.8sec), large (>10%) and reversible deformation of Poly(vinyl alcohol) gel (PVA) swollen with dimethyl sulfoxide (DMSO) upon electric field was realized, and the maximum observed strain reached quite high 27% (DP2100). St-PVA gels were found to exhibit more stable and reversible deformation than at-PVA gels. Furthermore, we have studied the macroscopic structure of PVA/DMSO gels and its influence on their strain exhibition. Four differently structured PVA/DMSO gels, monolayer, circular, triple-layered and porous, were prepared. Monolayer gel exhibited the highly reproducible strain behavior. The mechanism of electric actuation of PVA/DMSO gel is proposed. Then a design of gel mechanical switch is shown, which exhibited the fast response to the electric field with a large, stable and reversible stretching deformation.

Membrane potential generation without ion transport

Donnan theory and Goldman-Hodgkin-Katz equation (GHK eq.) state that the nonzero membrane potential is generated by the asymmetric ion distribution between two solutions separated by a semipermeable membrane and/or by the continuous ion transport across the semipermeable membrane. However, there have been a number of reports of the membrane potential generation behaviors in conflict with those theories. The authors of this paper performed the experimental and theoretical investigation of membrane potential and found that (1) Donnan theory is valid only when the macroscopic electroneutrality is sufficed and (2) Potential behavior across a certain type of membrane appears to be inexplicable on the concept of GHK eq. Consequently, the authors derived a conclusion that the existing theories have some limitations for predicting the membrane potential behavior and we need to find a theory to overcome those limitations. The authors suggest that the ion adsorption theory named Ling’s adsorption theory, which attributes the membrane potential generation to the mobile ion adsorption onto the adsorption sites, could overcome those problems.

Feedforward control of an Ionic Polymer-Metal Composite actuator

Current view about cell is that the cell is a watery solution coated with semi-permeable membrane and there exists nonzero potential, so-called membrane potential, across the semi-permeable cell membrane. Goldman-Hodgkin-Katz equation and Donnan theory are the fundamental existing theories for explaining the cause of membrane potential generation. However, the observations of membrane potential inexplicable by these existing theories have been repeatedly reported by a small number of researchers for more than the past half century. Hence, it is needless to say important to reconsider the membrane potential generation mechanism. Based on the experimental result shown in this paper, it was concluded that the existing theories were not genuinely right for the explanation of membrane potential generation. Adsorption theory is only a genuinely right theory instead. The adsorption theory describes that the adsorption of the mobile ions on the adsorption sites on the membrane generates the membrane potential. This work introduces the experimental observation inexplicable by Goldman-Hodgkin-Katz equation or Donnan theory but is in harmony with the adsorption theory.