Poly pyroelectricity

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.)... 

Figure 20 indicates the pyroelectric current in calender-rolled rigid poly (vinyl chloride) (PVQ (Furukawa and others, 1968). In Fig. 20, results are shown for fifteen specimens cut from a sheet of PVC film, with the polarity map as Fig. 21. The map shows a heterogeneity of polarity.

Fig. 20. Pyroelectric current of 15 specimens of poly(vinyl chloride) film cut out from a calender-rolled sheet as indicated in Fig. 21. Electrode area = 1 x 1 cm2 film thickness = 0.2 mm heating rate=6 K/min. Reproduced from Furukawa and others [J. Appl. Polymer Sci. 12,2675 (1968)] by permission of John Wiley Sons,...

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. 

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

The average spectral resolution was approx. 50 cm, limited by the sensitivity of the pyroelectric vidicon. The target, poly-vinylidene phthalate (PVH2), is approx, ten times less sensitive... 

Detection of heat generated by absorbed radiation converted nonradiatively has also been done using pyroelectric materials like )3-poly(vinylidene) fluoride onto... 

A major advance was made in 1969 when a strong piezoelectric effect was discovered in poly(vinylidene fluoride) (PVDF). The effect is much greater than for other polymers. In 1971, the pyroelectric properties of PVDF were also first reported, and as a consequence, considerable research and development has continued during the last two decades. 

Wegener M, Hesse J, Richter K, Gerhard-Multhaupt R (2002) Ferroelectric polarization in stretched piezo- and pyroelectric poly(vinylidene fluoride-hexafluoropropylene) copolymer films. J Appl Phys 92 7442... 

There is a real need for efficient pyroelectric materials for uncooled infrared detectors. At the moment, low-cost infrared cameras are made with poly(vinylidene fluoride-co-trifluoroethylene) [P(VF2-TrFE)] as the pyroelectric material. To take the place of P(VF2-TrFE), FLCPs have to exhibit a bet-... 

The third part deals with ferroelectric polymers and their pyroelectric properties. We describe the realization and performance of an IR pyroelectric sensor using copolymers of poly(vinylidene fluoride-ethylene trifluoride). 

The copolymers poly(vinylidene-fluoride-ethylene trifluoride). P(VP2-VF3) are ferroelectric and pyroelectric polymers. Thdr formula is represented below ... 

Ferroelectric composites are alternatives to standard piezoelectric and pyroelectric ceramics such as lead zirconate titanate (PZT) and BaHOs (BT). They combine the strong ferroelectric and dielectric properties of ceramics with the easy processing and good mechanical properties of polymers. Dispersion of micrometer-sized ferroelectric particles in an electrically passive epoxy matrix was first published by Furukawa et al. [1976] and later extended to ferroelectric matrices such as poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride-co-3-fluoroethylene) (PVDF-TrFE) [Hsiang et al., 2001 Hilczer et al., 2002 Gimenes et al., 2004 Lam et al., 2005 Beloti et al., 2006]. However, the necessity of miniaturization of electronic components and... 

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... 

The pyroelectric effect can also be employed as a sensor of an enzymic reaction. Dessy et al (57) placed two poly(vinylldene fluoride) films into contact, with one exposed surface coated with enzyme and contacting a flow injection sample stream. The potential resulting from the thermal bias across the films could be related to the enzyme substrate concentration. 

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]... 

---