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Shiomi Y.,Kansai University | Onishi K.,Kansai University | Nakiri T.,Kansai University | Imoto K.,Imoto Mechanical Engineering Co. | And 5 more authors.
Japanese Journal of Applied Physics

By using additives to change the higher-order structure of a poly(L-lactide) (PLLA) film, an improvement in its piezoelectricity was realized. The additive used was a triblock copolymer, which is a pure acrylic symmetric block copolymer consisting of a center block of poly(butyl acrylate) (PBA), corresponding to its soft part, and two side blocks of poly(methyl methacrylate) (PMMA), corresponding to its hard part. The triblock copolymer is hereafter denoted as PMMA-b-PBA-b-PMMA. The piezoelectric e-constant of the PLLA film with added PMMA-b-PBA-b-PMMA (PLLA/PMMA-PBA-PMMA film) was over two times higher than that of the PLLA film without adding PMMA-b-PBA-b-PMMA (reference PLLA film). Also, we found that the glass transition temperature increases with increasing PMMA-b-PBA-b-PMMA content. From atomic force microscopy (AFM) images, it was found that a new higher-order structure was formed in the PLLA/PMMA-PBA-PMMA film with high piezoelectricity. The method of using PMMA-b-PBA-b-PMMA has high productivity and its promising for industrial use. © 2013 The Japan Society of Applied Physics. Source

Ito S.,Imoto Mechanical Engineering Co. | Imoto K.,Imoto Mechanical Engineering Co. | Takai K.,Imoto Mechanical Engineering Co. | Kuroda S.,Imoto Mechanical Engineering Co. | And 6 more authors.
Japanese Journal of Applied Physics

To realize a new polymer sensor fabricated from a piezoelectric chiral polymer fiber, we attempted to detect the response signal induced by the shear piezoelectricity of the chiral polymer poly(L-lactic acid) (PLLA) under the application of stress and strain, and we confirmed that the piezoelectric response signal was sufficiently large for use as a sensor signal. We then prepared a left-hand helical torsion coil (PLLA fiber lefthand coil), which was formed by drawing a PLLA fiber ten times. It was observed that, when twisted and released suddenly, the coil exhibited a torsion vibration, and we confirmed that the piezoelectric response signal followed the torsion vibration. Next, we prepared a system in which a PLLA fiber coil was linked to a personal computer used for simple image processing. The PLLA fiber left- and right-hand coils were placed on the arm of a subject, and the inward rotation and outward rotation of the forearm and upper arm were measured. Finally, using this system, we were able to visualize the rotation of the forearm and upper arm. © 2012 The Japan Society of Applied Physics. Source

Yoshida T.,Imoto Mechanical Engineering Co. | Imoto K.,Imoto Mechanical Engineering Co. | Tahara K.,Imoto Mechanical Engineering Co. | Naka K.,Imoto Mechanical Engineering Co. | And 5 more authors.
Japanese Journal of Applied Physics

The piezoelectricity of a film of the eco-material poly(L-Lactic acid) (PLLA) with high transparency and flexibility has been noted for its possibility of application to new types of devices used in mobile equipment. However, for its application, there are many difficult problems to be solved, because the PLLA film has poor thermal stability. To change the high-order structure of the PLLA film, thus realizing an improvement in the temperature dependence of its piezoelectricity, a composite film with a stereocomplex crystal (SC) formed from PLLA and poly(D-lactide acid) (PDLA) molecules was fabricated. As a result, we obtained a composite film with a stable piezoelectric temperature dependence compared with a pure PLLA film. To analyze its piezoelectric temperature dependence, we first observed the high-order structure of the composite film using a polarized microscope (POM). However, we did not find any difference between the high-order structures of the composite film and the pure PLLA film. In contrast, from observation by atomic force microscopy (AFM), it was found that the grain structure in the composite film became more homogeneous than that in the pure PLLA film. These experimental results indicate that, by changing the high-order structure through a compound with SC, the external stress always has a constant effect over a wide temperature range and, as a result, the induced polarization is constant in the composite film. Thus, the composite film shows excellent thermal stability of piezoelectricity compared with the pure PLLA film. © 2010 The Japan Society of Applied Physics. Source

Yoshida T.,Chiyoda Corporation | Yoshida T.,Kansai University | Imoto K.,Imoto Mechanical Engineering Co. | Nakai T.,Imoto Mechanical Engineering Co. | And 7 more authors.
Japanese Journal of Applied Physics

We realized a multilayer film laminated alternately with poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) films in order to improve the piezoelectric performance of the PLLA film. In the fabrication processes, the thicknesses of PLLA and PDLA films were reduced to improve the effective electric field, and a multilayer composed of more than 100 layers (PDLA/PLLA multilayer film) was realized to improve the piezoelectric performance. In general, a single PLLA film has a piezoelectric constant of about 5 pC/N, and it is difficult to observe the piezoelectric resonance in this film of centimeter-order size using a commercial impedance analyzer because of its small Q-value. In contrast, the PDLA/PLLA multilayer film of centimeter-order size has a piezoelectric performance equivalent to that of the piezoelectric material with a piezoelectric constant of 100 pC/N, and also, the piezoelectric resonance can be observed in this film. On the basis of these results, we confirmed that even an object of 259 g mass is made to vibrate under the piezoelectric resonance vibration of this PDLA/PLLA multilayer film. In other words, necessary quantities for actual work as an actuator could be obtained in the PDLA/PLLA multilayer film. © 2011 The Japan Society of Applied Physics. Source

Tanimoto K.,Kansai University | Tanimoto K.,Mitsui Chemicals Inc. | Nishizaki H.,Kansai University | Tada T.,Kansai University | And 9 more authors.
Japanese Journal of Applied Physics

It has been reported that poly(ß-phenethyl L-aspartate) (PPLA) exhibits irreversible inversion from right-handed to left-handed helixes in a solid state at 130-140 °C from the results of circular dichroism measurement and X-ray diffraction. On the other hand, it is well known that semicrystalline chiral polymers show shear piezoelectricity due to their asymmetric crystal structure. The results of macroscopic shear piezoelectric measurement include information on macroscopic and microscopic properties due to the helix structure of the chain molecules. However, in general, no direct correspondence has been reported between the macroscopic piezoelectric properties and crystal characteristics because of the existence of a unique complex high-order structure in polymer films. We measured the temperature dependence of the piezoelectricity of a PPLA film in order to obtain more information concerning the helix inversion process. As a result, the sign inversion of the piezoelectric constant was observed at the temperature at which the helix inversion took place. It was also shown that the macroscopic orientation of the crystalline structure was maintained in the PPLA film after the sign inversion, even though molecular motion such as the segmental motion and side-chain motion of PPLA molecules was activated © 2014 The Japan Society of Applied Physics. Source

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