The piezoelectric properties and ferroelectric transition behaviors of vinylidene fluoride and trifluoroethylene copolymers, P(VDFx−TrFE1−x), were studied as a function of x in the range of x=0.37–0.94. The electromechanical coupling factor kt and piezoelectric constant d31 are strongly dependent on both x and annealing temperature. In the copolymers of 0.65≲x≲0.82, a large kt value of 0.27–0.3 has been found when annealed above ferroelectric-to-paraelectric transition temperature Tc. The large kt is attributable to their high remanent polarization (∼110 mC/m2) which arises from high degrees of crystallinity and preferred orientation of well-grown crystallites. Structural and morphological changes induced by annealing and poling were characterized by SEM, DSC, and x-ray diffraction studies. Phase diagram of the copolymers were obtained by DSC measurements. Tc increases with increase of x and coincides with melting temperture Tm at x≂0.82. In the range of x≳0.82, Tc=Tm.

Elastic, dielectric, and piezoelectric constant matrix elements of a “single crystalline’’ (SC) film of vinylidene fluoride trifluoroethylene copolymer, P(VDF/TrFE), in which the orthorhombic [001] and [110] axes of fully extended chain crystals are preferentially oriented parallel to the stretching axis and normal to the surface, respectively, were measured at temperatures ranging from 10 K to the Curie point (402–404 K) by using a piezoelectric resonance method. All of the electromechanical coupling factors (k31, k32, k33, k24, and k15) are larger than those of conventional lamellar crystalline films. Some of the matrix elements for a P(VDF/TrFE) single crystal are derived from the measured values of constant matrix elements for the SC film. Some features characteristic of the SC film are revealed. The SC film has a large Young’s modulus for the stretching direction (1/s11) (121 GPa at 10 K). The properties related to the molecular motions along the chain axis, such as 1/s11, shear stiffness constant c55, shear piezoelectric constant e15, etc., exhibit strong relaxations around 250 K. The origin of these relaxations in the crystalline phase is discussed.

Field-induced phase transformation and thermally induced phase transition in vinylidene fluoride (VDF) and trifluoroethylene copolymers with VDF content higher than 82 mol% and their ferroelectric and piezoelectric properties have been studied by means of x-ray diffraction, DSC, D-E hysteresis, and piezoelectric resonance. It is found that copolymers with VDF content ranging from ∼82 to 90 mol% crystallize under ordinary pressure into thick lamellar single crystals composed of a mixture of α, β, and possibly γ phases. Application of a strong ac electric field transforms these mixed phase crystals into β-phase crystals completely. The β-phase crystals are ferroelectric and exhibit strong piezoelectric activity stable up to the melting temperature (160–180  °C depending on VDF content); the Curie point coincides with the melting point. Unpoled, mixed phase film has a paraelectric or rotational phase below the melting temperature, in which thick lamellar single crystals are grown extensively, whereas β-phase film prepared by mechanical drawing has no paraelectric phase below the melting point. Definite ferroelectric-to-paraelectric phase transition in P(VDF-TrFE) is inferred to occur only in thick lamellar crystals grown in the paraelectric phase. A phase diagram of P(VDF-TrFE) is described.

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We construct a kink solution on a non-BPS D-brane using Berkovits' formulation of superstring field theory in the level truncation scheme. The tension of the kink reproduces 95% of the expected BPS D-brane tension. We also find a lump-like solution which is interpreted as a kink-antikink pair, and investigate some of its properties. These results may be considered as successful tests of Berkovits' superstring field theory combined with the modified level truncation scheme.

Preconditioning improves energy metabolism during reperfusion, although it does not attenuate myocardial stunning for at least 2 hours after reperfusion.

A large electromechanical coupling factor k t of about 0.3 has been found in vinylidenefluoride and trifluoroethylene copolymers containing 70–80 mol% VDF. These copolymers exhibit clear ferroelectric behavior. The strong piezoelectricity and distinctive ferroelectricity are attributable to high crystallinity, strong preferred orientation, and reduced conformational defects in crystallites, which are induced by annealing and successive or simultaneous poling. The polarization is inferred to grow through rotation of the polar axis by nπ/3 about the molecular axis (c-axis) under an external electric field above the coercive field.

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