VDF-TrFE copolymer

We compare two devices the ferroelectric OFET of Figure 21.12 and a similar OFET, without the ferroelectric P(VDF-TrFe) copolymer, for f/pg = -50 V, without gate bias. 

For commonly used poly(vinylidene fluoride trifluoroethylene), abbreviated as P(VDF-TrFE), copolymers with a VDF content ranging from 50 to 85 mol%, the ferroelectric beta phase is stable at room temperature, and a transformation to the paraelectric alpha phase occurs above the Curie point but below the melting point [89]. Above the Curie temperature, a transition between the paraelectric and... 

Relaxor ferroelectric polymers are intimately related to the ferroelectric polymers described above. All known relaxor ferroelectric polymers are based on the P(VDF-TrFE) copolymer. As the name suggests, these polymers behave as relaxor ferro-electrics, which is distinguished by a broad peak in dielectric constant and a strong frequency dispersion [99,100]. There are two major limitations of the P(VDF)-based ferroelectric actuators. First, the electrically induced paraelectric-ferroelectric transition that allows for actuation only occurs at temperatures above the Curie... 

Fig. 1.5 Actuation strain as a function of electric field for irradiated P(VDF-TrFE) copolymer (2), P(VDF-TrFE-CTFE) (4), P(VDF-CTFE) (5), and P(VDF-TrFE-CFE)...

In this article, we introduce a recently developed ultrasonic spectroscopy method and review its application to polymeric studies. First, the principle of this ultrasonic spectroscopy is explained including the instruments and data analysis methods. Then, actual application of this measuring system is described for the characterization of solid polymers and the observation of phase transition phenomenon in liquid crystals and ferroelectric (VDF/TrFE) copolymer. Finally, the extension of this system to two-dimensional measuring and the application to non-destructive testing of CFRP (carbon fiber reinforced plastics) are discussed. 

A copolymer of vinylidene fluoride-trifluoroethylene (VDF/TrFE) copolymer is well known as the polymer for which a clear Curie point was found for the first time in an organic material. At this Curie point, the polymer undergoes a solid-to-solid phase transition from paraelectric to ferroelectric phases with decreasing temperature. Therefore, the changes in the physical properties such as crystal structure, electrical and thermal properties upon the ferroelectric phase transition have drawn many researchers interest. Here, the results concerning the ultrasomc spectroscopic mvestigation on acoustic and viscoelastic behaviour around the ferroelectric phase transition region of this copolymer are described [15]... 

Fig. 15. Ultrasonic waveforms observed for P(VDF/TrFE) copolymer at three different temperatures below, around, and above the ferroelectric phase transition point...

Fig. 16. Temperature and frequency dependence of absorption in P(VDF/TrFE) copolymer at the ferroelectric phase transition region...

Fig. 17. Temperature dependence of absorption at several frequencies at the ferroelectnc phase transition region of P(VDF/TrFE) copolymer...

H. Kodama, Y. Takahashi, T. Furukawa Effects of Annealing on the Structure and Switching Characteristics of VDF/TrFE Copolymers, Ferroelectrics 205, A33 (1997)... 

First ferroelectric polymer - polyvinilidene fluoride (PVDF or PVF2) - was discovered in 1969. Extensive research has been focused on this substance and their copolymers withtrilluoroethylene (TrFE) since that time. Due to its resistivity to the harmful chemical substances is this polymer used in stractural coatings to prevent damage. Another excellent functional property is a veiy low value of the acoustic impedance, which allows for the better acoustic matching to water environment. Due to this property P(VDF/TrFE) copolymer is being applied mostly in hydrophones (Nalwa 1995) and ultrasound imaging transducers. PVDF polymer and its blends with TrFE are commercially available in the market. 

Since the discovery of high piezoelectricity more than 30 years ago, there have been many improvements. These include preparation of copolymers with trifiuoroethylene (TrFE) and chlorofiuoroethylene. Recently, it was demonstrated that, by appropriate high-energy electron irradiation treatment, the piezoelectric P(VDF-TrFE) copolymer can be converted into an electrostric-tive polymer with still greater sensitivity (82). 

By varying the film processing conditions, the transverse strain in an irradiated P(VDF-TrFE) copolymer can be tuned over a wide range. For instance, the transverse strain response in unstretched films is relatively small ( +1 % at -100 MV/m), with an... 

High-Energy-Electron Irradiated (HEEl) P(VDF-TrFE) Copolymers. 524... 

Bharti V et al (2000) Polarization and structural properties of high energy electron irradiated P(VDF-TrFE) copolymer films. J Appl Phys 87 452-461... 

Cheng Z et al (1999b) Transverse strain responses in the electrostrictive P(VDF-TrFE) copolymer. Appl Phys Lett 74 1901-1903... 

Galetti P et al (eds) (1988) Piezoelectric and ferroelectric properties of P(VDF-TrFE) copolymers and their pUcation to ultrasonic transducers. In Medical apphcations of piezoelectric polymers gordon and breach. New York... 

Ferroelectric phase transition of VDF-TrFE copolymers is affected by many factors. 

As staled above, a characteristic feature of ferroelectric material b an invenion of the dipole under application of an electric field. In the case of VDF-TrFE copolymers, loo, an inversion of CFj dipoles has been observed with many measurements, including X-ray di action [46,175,176], infrared spectra [177,178], and NMR spectra [179]. 

Vinylidcnc fluoridc-tetrafluoroethylene (VDF-TFE) copolymers exhibit similar ferroelectric phase transitions as do VDF-TrFE copolymers, but the behavior is rather different depending on the VDF content (190-195). 

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