Motility of Artificial Muscle using Charge Injection -Solvent Drag by Applying an Electric Field

研究涵盖了从高度膨胀的聚合物凝胶到非溶剂型聚氨酯弹性体的广泛材料，并包含了各种类型的变形，大应变有时超过400%，这可能是目前的主要数据。对于凝胶材料的驱动，有各种各样的触发器。高分子凝胶是指高分子材料在大量溶剂的作用下膨胀后，通过大分子链之间的化学或物理交联仍能保持其形状。体积主要取决于凝胶中的溶剂含量，这意味着溶胀和收缩运动可以通过溶剂和聚合物之间的相互作用来控制。溶剂组成、pH、离子强度、温度等因素都能影响溶剂与聚合物的相互作用，说明控制参数的变化范围很广。在这些膨胀的凝胶中，凝胶中的压力分布是均匀的。当我们可以控制凝胶中的压力分布时，凝胶可以在不改变溶剂含量的情况下变形。为了在不改变体积的情况下实现变形，电场、磁场、光照射等物理触发是方便的。在电场应用方面，对聚电解质凝胶进行了大量的研究工作。在聚电解质凝胶的电致动过程中，不仅凝胶内部压力分布不对称，而且在变形过程中膨胀和溶胀也发生了迁移。此外，变形过程伴随着电极上的电化学反应，是一种不可逆的化学过程或化学消耗，限制了材料的使用寿命。为了克服聚合物凝胶作为致动器的困难，我关注了非离子型聚合物凝胶，这种聚合物凝胶不会发生明显的化学反应或消耗。我们发现与传统凝胶相比，反应速度更快，应变更大。作为静电力的应变太大，而电能耗散似乎很小。除了这些优点之外，电介质凝胶可以在没有水或含水成分存在的空气中被驱动。它们的存在在聚电解质凝胶或导电聚合物致动器中是不可避免的。用二甲基亚砜（DMSO）膨胀聚乙烯醇（PVA）凝胶时，凝胶不仅在电场方向上收缩，而且由于凝胶内不对称的压力分布而发生弯曲。凝胶中不对称应变的原因是电荷注入和溶剂迁移。我把这个驱动过程称为“电荷注入-溶剂-拖拽”方法。这种方法可以使放置在电极阵列上的凝胶变形。变形看起来像“爬行”的蠕虫。通过溶剂阻力理论，可以定量地估计出应变。有趣的是，凝胶中的溶剂运动可以通过电场作用下的溶剂迁移来估计。这一分析表明，我们可以通过电致应变来估计聚合物的网络密度。以增塑型聚氯乙烯（PVC）为例，结果表明，在施加电场的情况下，PVC会出现“爬行”变形。这种变形看起来像变形虫体内的“伪浆流”，但它是可逆的，一旦磁场消失，它就会恢复原来的形状。我们把这种变形称为“电趋向性”，类似于生物系统中的趋化性。蠕变变形可应用于类节理弯曲变形。在这种情况下，在变形中观察到的电流在几十nA的范围内。弯曲速度非常快，可在30毫秒内达到100度，具体取决于所使用的增塑剂。这种情况下与PVA-DMSO凝胶的主要区别是没有溶剂阻力，换句话说，溶剂迁移仅限于伴随聚合物网络的电极表面。类似的变形也可以在其他塑化聚合物中成功诱导。对于有效的变形，已经阐明了电极的不对称是有效运动的关键。在聚氨酯弹性体中，我们将其作为非溶剂型电致动器进行研究，因为我可以期望分段聚氨酯弹性体作为一种增塑化聚合物。与塑化聚合物的区别可能是聚合物链的可变形性受到共价键的严格限制。我们期望弹性体的物理性能可以按照我们的愿望进行控制，但到目前为止，我们还没有达到最理想的状态。变形的主要原因是空间电荷积聚及其不对称分布。但在寻找弹性体电活性的过程中，我们发现了应变记忆、添加剂对弯曲方向的控制、化学结构的影响等。少

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 … More 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