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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.

To realize a new piezoelectric chiral polymer actuator, we studied the motion induced by the shear piezoelectricity of a poly(L-lactic acid) (PLLA) film under the application of an ac voltage. First, PLLA was subjected to a supercritical CO2 treatment to change its high-order structure, resulting in an improvement in its piezoelectricity. Then, we designed a PLLA film roll transducer, which consisted of a piece of the treated PLLA film rolled into a long thin roll. To demonstrate the transducer, we placed it vertically on a fixed stand. A plastic hemispherical container was placed on the upper end face of the transducer. It was found that the container rotated smoothly in the counterclockwise direction when an ac voltage was applied. We emphasize that no special complex mechanical parts were used in this study.

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