The linear and nonlinear dielectrical and depolarization processes of the copolymer of vinylidene fluoride and trifluoroethylene have been measured. The D vs. E hysteresis loop below room temperature indicates the ferroelectricity of this copolymer. The dielectric anomaly and the disappearance of remnant polarization at T0=70°C suggest that T0 is the phase transition temperature from the ferroelectricity to the paraelectricity phase. Results are analyzed on the basis of Weiss-type semimolecular theory.

Poly(lactic acid) (PLA) is a widely used biomass-derived polymer. It is chiral because the lactic acid monomer has an asymmetric carbon. If the L-lactide is polymerized, then the PLA polymer is an L-type PLA or poly(L-lactic acid) (PLLA); if the D-lactide in PLA is polymerized, then the polymer is a D-type PLA (PDLA). When these polymers undergo drawing or elongation, they exhibit shear piezoelectricity. PLA films are highly transparent and do not exhibit pyroelectricity because of the lack of intrinsic polarization. Therefore, if a PLLA film is used for a touch panel, which is operated by pressure, there is no spurious signal due to heating from the fingers. This suggests that PLLA films may be suitable for touch panels using pressure detection. We used PLLA as the base film of a projected capacitive touch panel with multiple electrodes, and demonstrated a multitouch gesture screen that was sensitive to pressure applied on the screen. This touch panel technology has potential applications for smart phones and tablet personal computers. #

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Recently, the application of uniaxially stretched poly(L-lactic acid) (PLLA) films to speakers, actuators, and pressure sensors has been attempted, taking advantage of their piezoelectric performance. However, the shear piezoelectric constant d 14 of uniaxially stretched PLLA film is conventionally 6-10 pC N %1 . To realize a high sensitivity of pressure sensors, compact speakers, and actuators, and a low driving voltage, further improvement of the piezoelectric performance is desired. In this study, we carried out solid-state extrusion (SSE) to stretch and orient poly(Dlactic acid) (PDLA) and verified its effects on piezoelectric performance. By SSE, we were able to improve the mechanical strength and elastic modulus of PDLA samples. Furthermore, the d 14 of the samples was significantly increased to approximately 20 pC N %1 .

Poly-L-lactic acid (PLLA), which is a type of chiral polymer, exhibits a high shear piezoelectric constant. To realize a higher shear piezoelectric constant, we spun PLLA resin into fibers. We succeeded in controlling the piezoelectric motion of a PLLA fiber by applying a dc voltage and ac voltage, similar to the control of a piezoelectric actuator. On the basis of this experimental result, we designed a catheter using a PLLA fiber (PLLA fiber catheter) and tweezers using a pair of PLLA fibers (PLLA fiber tweezers), controlled by adjusting the applied voltage. Then, using the PLLA fiber tweezers or catheter, we successfully picked up and removed small samples, such as a thrombosis in a blood vessel.

Poly-L-lactic acid (PLLA) has recently attracted attention as a polymer which exhibits a high shear piezoelectric constant. In this study, it was possible to control the piezoelectric motion of the PLLA fiber by applying d.c. voltage and a.c. voltage similar to a piezoelectric actuator. Then, on the basis of the experimental results, an electric control catheter and tweezers, using PLLA fibers (PLLA fiber catheter/tweezers) was developed. In the demonstration, it was assumed that thrombosis in blood vessels occurred and it was attempted to remove the thrombosis from the affected area using the PLLA fiber catheter and tweezers. This very delicate operation was attempted under a microscope. Using the PLLA fiber catheter and tweezers, the affected area was excised. A video movie of the test demonstration was recorded using a CCD video camera. All stages proceeded well in this study.

Ferroelectric copolymers of vinylidene fluoride with trifluoroethylene and tetrafluoroethylene have been investigated by means of broad band dielectric spectroscopy (10 mHz-1 GHz) at temperatures covering the ferroelectric, paraelectric and molten phases as well as the glassy and rubbery states. The low-temperature relaxation spectra near T, (--40°C) consist of two processes; a WLF-type segmental mode and an Arrhenius type local mode. These processes are unified near room temperature to be transferred continuously to the high-temperature process. After showing a peak at the Curie point T, (70-140"C), the relaxation strength decreases gradually in the paraelectric phase until the melting point T, (-150°C) is reached, where it decreases rapidly. It is found that the relaxation time in the molten phase lies on the Arrhenius line extended from the low-temperature local mode process. This implies that related molecular motions arise from a common elementary process. Departure from this Arrhenius line in the paraelectric phase is discussed by the use of a cooperative multi-site model.

The measurement of the temperature dependence of elastic, dielectric, and piezoelectric constants for the film of 55/45% VDF-TrFE copolymer suggests that the Curie temperature exists at about 70 °C. The lattice spacing sharply changes at a temperature range from 55 to 75 °C. The remanent polarization is also determined from the D versus E hysteresis loop below 75 °C. It is found that the spontaneous strain in crystal lattice is linearly related to the square of remanent polarization. The transition is ascribed to electrostriction due to dipolar orientation.