| Budget Amount *help |
¥7,800,000 (Direct Cost: ¥7,800,000)
Fiscal Year 2003: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2002: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 2001: ¥2,600,000 (Direct Cost: ¥2,600,000)
Fiscal Year 2000: ¥2,500,000 (Direct Cost: ¥2,500,000)
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| Research Abstract |
The investigations covered wide range of materials from highly swollen polymer gels to non-solvent type of polyurethane elastomers and contained various types of deformations with large strains sometimes exceed 400%, which might be the champion data at this moment.
For the actuations of gel materials, there are wide variety of triggers. Polymer gels are defined as polymer materials swollen with large amount of solvent and still hold their shapes with chemical or physical crosslinks among the macromolecule chains. The volume depends mainly on the solvent content in the gel, meaning the swelling and contractile motility can be controlled by the interaction between the solvent and polymer. The interaction between solvent and polymer can be affected by solvent composition, pH, ionic strength, temperature etc., suggesting that the variety of controlling parameter is wide.
In these swollen gels, the pressure distribution is uniform in the gels. When we can control pressure distribution in the
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gel, the gel can be deformed without the change in solvent content. To attain the deformation without the volume change, the physical triggers like electric field, magnetic field and light irradiation are convenient. On electric field application, many works have been carried out on polyelectrolyte gels. In the electrical actuation of polyelectrolyte gels, again not only the asymmetric pressure distribution in the gels but also the swelling-and-deswelling migrated in the deforming processes. Moreover, the deforming process accompanies electrochemical reactions on the electrodes, which is an irreversible chemical process or chemical consumption that limit the life span of the materials.
To overcome the difficulties of polymer gels as an actuator, I paid attention on non-ionic polymer gels, in which no explicit chemical reaction or consumption could be expected to occur. We found far much quicker response and larger strain compared to the conventional gels. The strain was too large as an electrostatic force and electrical energy dissipation seemed to be very small. In addition to these advantages, the dielectric gels can be actuated in air without the presence of water or aqueous components. Their presence have been known to be inevitable in polyelectrolyte gels or conductive polymer actuators. In the case of poly(vinyl alcohol)(PVA) gel swollen with dimethyl sulphoxide (DMSO), the gel contracts not only in the direction to the electric field, but also can bend by an asymmetric pressure distribution in the gel. The cause of the asymmetric strain in the gel turned out to be charge injection and solvent migration. I call the actuation procedure as "charge-injected-solvent-drag" method. This method can deform the gel laid on an electrode array. The deformation looks like "crawling" worm. The strain can be quantitatively estimated theoretically by the theory of solvent drag. It is interesting to mention that the solvent motion in the gel can be estimated from the solvent migration under the electric field. This analysis suggests that we can estimate the polymer network density by the electrically induced strain.
In the case of plasticized poly(vinyl chloride)(PVC), it turned out that the PVC shows "creeping" deformation by applying an electric field. The deformation looks like "pseudoplasmic flow" in amoeba, but it is reversible and restores the original shape as soon as the field is off. We call this deformation as "electrotaxis" in analogy to chemotaxis in biological system. The creep deformation can be applied to joint-like bending deformation. In this case current observed in the deformation is in the range of tens of nA. Bending rate is very swift, and can reach 100 degree in 30 ms, depending on the plasticizer employed. Major difference in this case from PVA-DMSO gel is the absence of the solvent drag, in other words, solvent migration is limited on only the electrode surface accompanying polymer network. Similar deformation could also be successfully induced in other plasticized polymers. For the efficient deformation, it has been elucidated that the electrode asymmetry is critical for the efficient motility.
In the elastomer of polyurethane, we investigated it as non-solvent type electroactive actuator, since I can expect the segmented polyurethane elastomer as a kind of plasticized polymer. The difference from plasticized polymer might be the deformability of polymer chains that are strictly restricted by covalent bonding. We expect the physical properties of the elastomer can be controlled as we wish, but so far the most desirable has not been attained yet. Principally, the deformation is suggested to originate from space charge accumulation and its asymmetric distribution. But in the course of searching the electroactive properties of the elastomers, we found strain memory, bending direction control by additives, effect of chemical structures etc. Less
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