Poly piezoelectric constant

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... 

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

Poly-L-lactic acid is a chiml polymer with two optical isomers, and its chain molecules form a helical structure owing to its chiraUty. One is PLLA and the other is poly-D-lactic acid (PDLA). The helical structure of PLLA is right handed, whereas the hehcal structure of PDLA is left handed. The shear piezoelectric constant of PLLA is high compared with those of other shear piezoelectric polymers, as shown in Table 5. 

K. Ihshiro and H. Ihdokoro, Esttraaiiiig the limiting values of the macrosooptc piezoelectric constants of poly(vinylideiic fluoride) form I, Maemmolectiles 76 961 (1983X... 

Figure 17 shows that the two kinds of piezoelectric constants are almost unchanged in the temperature range from room temperature to about 2(XfC. The dynamic piezoelectric stress constant e ]/ + ku expresses a coefficient fur electric displacanent divided by strain. The dynamic piezoelect strain consunt expresaes a coefficient for electric displacement divided by stress. The excellent thermal stability of aromatic poly-urea is noticeable. 

Rgura 20 Temperature dqKodeocc of piezoelectric constant for magnetically oriented film of poly- Y-beazyl-L- ulamBie. (From Ref. S3.)... 

Ihble 2 shows a comparison of physical quantities for three optically active polymers described above. With an increase of polarity in chemical structure, the magnitude of the piezoelectric constant increases remarkably, although the degree of crystallinity and the degree of orientation are not exactly the same for the three polymers. The chemical structure of poly-lactic acid is the simplest form to oou de an asymmetric carbon atom and a polar group CO-O and is most suitable for displaying the piezoelectric effect in this aeries. 

The theory of spherical diqtersion has been applied successfully to some oriented polymers, and the piezoelectric constants for the crystalline phase have been estimated. However, there still remain problems such as the interface between the crystalline phase and the amorphous phase. Actually, for oriented films of poly- y-benzylglutamale. the simple spherical dispersion model is not applied satisfactorily, and the extended three-element model, taking account of grain boundaries, has lo be introduced to explain the etywrimental results. Further elaboration of this model would be useful to understand the texture and properties of a composite such as a mixture of piezoelectric ceramic particles and polymers. 

Because of the relatively small magnitmks of piezoelectric constants, practical ap> plications have not progressed so br. A trial micraphone using an elongated film erf poly- y-methylghitamate was repotted (52]. 

Another matrix based on biosources, poly(lactic acid) (PLA), has also been used as a suitable candidate for mechanical energy harvesting. Here, the presence of PLA in the form of fibers and embedded BaTi03 ceramic particles exhibit a piezoelectric constant per weight that is 2 orders of magnitude larger than those of crystal BaTi03 films (Morvan et al., 2012). 

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). 

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.

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)...

Nakamura, K., Wada,Y. Piezoelectricity, pyroelectricity, and the electro- striction constant of poly(vinylidene fluoride). J. Polymer Sci. A-2, 9, 161 (1971). 

Fig. 4. The effect of temperature on the piezoelectric strain constant, d3v for A, nylon-11 B, nylon-7 and C, poly(vinylidene...

Piezoelectricity links the fields of electricity and acoustics. Piezoelectric materials are key components in acoustic transducers such as microphones, loudspeakers, transmitters, burglar alarms and submarine detectors. The Curie brothers [7] in 1880 first observed the phenomenon in quartz crystals. Langevin [8] in 1916 first reported the application of piezoelectrics to acoustics. He used piezoelectric quartz crystals in an ultrasonic sending and detection system - a forerunner to present day sonar systems. Subsequently, other materials with piezoelectric properties were discovered. These included the crystal Rochelle salt [9], the ceramics lead barium titanate/zirconate (pzt) and barium titanate [10] and the polymer poly(vinylidene fluoride) [11]. Other polymers such as nylon 11 [12], poly(vinyl chloride) [13] and poly (vinyl fluoride) [14] exhibit piezoelectric behavior, but to a much smaller extent. Strain constants characterize the piezoelectric response. These relate a vector quantity, the electrical field, to a tensor quantity, the mechanical stress (or strain). In this convention, the film orientation direction is denoted by 1, the width by 2 and the thickness by 3. Thus, the piezoelectric strain constant dl3 refers to a polymer film held in the orientation direction with the electrical field applied parallel to the thickness or 3 direction. The requirements for observing piezoelectricity in materials are a non-symmetric unit cell and a net dipole movement in the structure. There are 32-point groups, but only 30 of these have non-symmetric unit cells and are therefore capable of exhibiting piezoelectricity. Further, only 10 out of these twenty point groups exhibit both piezoelectricity and pyroelectricity. The piezoelectric strain constant, d, is related to the piezoelectric stress coefficient, g, by... 

EFFECTS OF POISSON S RATIO AND ELECTROSTRICTION CONSTANT ON PIEZOELECTRICITY IN POLY(VINYLIDENE FLUORIDE)... 

Poly(vinylidene fluoride)(PVDF) is one of the most polar polymers among synthetic polymers and shows the most unique phenomena in many fields of pol3nner science. Especially, the electrical properties of PVDF have been the subject of intensive investigations in recent years since it was reported that it could exhibit a large dielectric constant and internal polarization for its B-form films, a very large piezoelectric and pyroelectric effects for polarized monoaxially and biaxially stretched films.[1,2,3]... 

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