Poly piezoelectric

Figure 4.3 Piezoelectric poly(vinylidene difluoride) PVDF and its non-piezoelec-tric isomer, poly(ethylene-co-tetrafluor-oethylene) (ETFE) [6].

Piezoelectric Poly(vinylidene fluoride) in Small-Bore, Thick-Walled Tubular Form... 

Li, J.Y. 2000. The effective electroelastic moduli of textured piezoelectric poly crystalline... 

Shimono, T, Matsunaga, S., Fukada, E., Hattori, T, and Shikinami, Y., The effects of piezoelectric poly-L-lactic acid films in promoting ossification in vivo. In Vivo, 10, 471-476 (1996). 

Piezoelectric Poly(Vinylidene) Fluoride (PVDF) in Biomedical Ultrasound Exposimetry... 

Ando M, Kawamura H, Tajitsu Y et al (2013) A deformation detection touch panel using a piezoelectric poly(L-lactic acid) film. In Proceedings of the 20th international display workshop, Sapporo Convention Center, Sapporo, 4-6 Dec 2013 Bergman J et al (1971) Pyroelectricity and optical second harmonic generation in polyvinylidene fluoride films. Appl Phys Lett 18 203... 

J. P. Luongo, Far-infrared spectra of piezoelectric poly vinylidene fluoride, J. Polymer ScL A-2 70 1119 (1972)... 

T. T. Ik ng. Aging behavior of piezoelectric poly(vinylideae fluoride) films irradiated by y rays, J. Polymer ScL, Polymer Lett Ed 79 289 (1981) Properties of piezoelectric poly(vinylid fluoride) films irradiated by yrays, Fermelectria 47 213 (1982)... 

Correia, D.M., Ribeiro, C., Sencadas, V., VUdngsson, L., Oliver Gasch, M., Gomez RibeUes, J.L., et al., 2016. Strategies for the development of three dimensional scaffolds from piezoelectric poly(vinylidene fluoride). Mater. Des. 92, 674—681. 

Ribeiro, C., Correia, D.M., Ribeiro, S., Sencadas, V., Botelho, G., Lanceros-Mendez, S., 2015a. Piezoelectric poly(vinyhdene fluoride) microstructure and poling state in active tissue engineering. Eng. Life Sci. 15 (4), 351-356 (Review). 

Polymer Ferroelectrics. In 1969, it was found that strong piezoelectric effects could be induced in the polymer poly(vinyhdene fluoride) (known as PVD2 or PVDF) by apphcation of an electric field (103). Pyroelectricity, with pyroelectric figures of merit comparable to crystalline pyroelectric detectors (104,105) of PVF2 films polarized this way, was discovered two year later (106.)... 

Typical piezoelectric materials are ceramic crystals and copolymers, such as poly(vinyHdene fluoride-i o-trifluoroethylene),... 

Just as an example, the X-ray diffraction patterns of compression moulded samples of PVDF, poly(vinylfluoride), and of some VDF-VF copolymers of different compositions are shown in Fig. 17 [90]. The degrees of crystallinity of the copolymer samples (40-50%) are high and analogous to those of the homopolymer samples. This indicates a nearly perfect isomorphism between the VF and VDF monomeric units [90, 96], The diffraction patterns and the crystal structures of the copolymers are similar to those of PVF, which are in turn similar to the X-ray pattern and crystalline structure of the P form of PVDF. On the contrary, the X-ray pattern of a PVDF sample crystallized under the same conditions (Fig. 17 a) is completely different, that is typical of the non-piezoelectric a form [90]. 

Ferroelectrics Poly(vynidilene fluoride) undergoes electrostriction when subjected to high ac fields, thus can be made into actuators applied pressure produces a piezoelectric response useful in sensors. 

We have had smart materials as materials for a long time though the term is relatively new. Some of the first smart materials were piezoelectric materials, such as poly(vinylene fluoride), which emit an electric current when pressure is applied and change volume when a current is passed through it. Most smart materials are polymeric or have a critical portion of the smart system that is polymeric. 

Values of piezoelectric constants are, however, very scattered among polymers. In the case of oriented poly(y-methyl L-glutamate) film, the piezoelectric strain constant (d-constant) amounts to as much as 10 x 10 8 cgsesu when elongated in a direction at 45° to the draw-axis (Fukada, 1970), which is comparable with d = 6.5 x 10 8 cgsesu for X-cut... 

The anisotropy of piezoelectricity in oriented polymer films is quite different among polymers. The piezoelectric effect in oriented polypeptide films is greatest when elongated along a direction at 45° to the draw-axis. On the contrary, the effect is most remarkable for elongation along the draw-axis for roll-drawn poly(vinylidene fluoride) film. 

As will be shown in the theory, the electrostriction effect plays an important role in the piezoelectric effect of polymer films. Moreover, a knowledge of the complex electrostriction constant as a function of frequency reveals a new aspect of the relaxational behavior of polymers. In this review a new method for measuring complex electrostriction constant with varying frequency will be presented with some results for poly(vinylidene fluoride). 

Even for poly(y-methyl L-glutamate) with a high piezoelectric constant (d= 10 7 cgsesu), the electro-mechanical coupling constant k defined by... 

Fig. 9. Piezoelectric strain constant of uniaxially drawn poly(y-methyl L-glutamate) film (a-helical form) plotted against the angle 6 between draw-axis and stress direction. Draw-ratio = 2. Drawn after Fukada, Date, and Hirai [Nature 211, 1079 (1966)] by permission of Macmillan (Journals) Ltd.

Fig. 11. Complex piezoelectric strain constant (20 Hz), complex Young s modulus (30 Hz), and complex dielectric constant (1kHz) of uniaxially drawn poly(D-propylene oxide) film plotted against temperature. Draw-ratio = 1.5. Degree of crystallinity=40%. Drawn after Furukawa and Fukada [Nature 221,1235 (1969)] by permission of Macmillan (Journals) Ltd.

A close correlation between the polarities of piezoelectricity and pyroelectricity was found for PVC and poly (vinylidene fluoride) (PVDF) films (Nakamura and Wada, 1971). However, it must be emphasized that the polarity of piezoelectricity is determined not only by the polarity of the charge distribution but also by that of heterogeneous strain. The origin of heterogeneous strain in the elongation of film may derive from heterogeneity in the structure of the film. 

Wada and others (1966) indicated that the piezoelectricity of poly-oxymethylene (POM) markedly increases when a temperature gradient has been applied during the casting process, probably because of the thermal diffusion of ions in the film. 

Kawai (1) and (2) (1969) found that polar polymer films such as PVDF, poly (vinyl fluoride), PVC, nylon 11, and polycarbonate exhibit a strong piezoelectricity when they are drawn and then polarized under a high cLc. field Ep at a high temperature Tp and cooled keeping the d.c. field. The piezoelectricity thus obtained depends on Ep, Tp, and poling period. An improved poling technique was reported by Edelman, Grisham, Roth, and Cohen (1970). 

Fig. 26. Correlation between increment of spontaneous polarization from 80° C to 15° C and piezoelectric strain constant at room temperature for /9-form polarized poly(vinylidene fluoride) films. Poling temperature = 90° C. Poling field = 700 kV/cm (Murayama, 1972)...

Fig. 28. Piezoelectric stress constant obtained from inverse piezoelectric effect and electrostriction constant of drawn and polarized poly(vinylidene fluoride) film plotted against temperature. Draw ratio = 7. Polarized at 90° C under the field of 400 kV/ctn for 3 hours. Frequency of applied voltage = 37.5 Hz. (Oshiki and Fukada, 1971) Broken line represents dielectric constant at 21.5 Hz for roll-drawn poly (vinylidene fluoride) film (Peterlin and Eiweil, 1969)...

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