Pyroelectric effect fluoride

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]... 

This area does not address the wide variety of devices that feature ferroelectric polymers as detectors based on their inherent pyroelectric effect. Instead, the focus of this chapter is to present recent (within the last decade) poly(vinylidene fluoride) (PVDF) transducer applications that feature their fenoelectiic effect as the preferred active material property. 

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.)... 

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. 

A laser flash technique has been used to determine the diffusivity of pyroelectric polymers such as polyvinylidene fluoride [83], whereas hot-wire techniques have been used to determine the thermal diffusivity of high-density polyethylene, low-density polyethylene propylene, and polystyrene [83], Dos Santos and coworkers [84] utilized the laser flash technique to study the effect of recycling on the thermal properties of selected polymers. Thermal diffusivity expresses how fast heat propagates across a bulk material, and thermal conductivity determines the woiking temperature levels of a material. Hence, it is possible to assert that those properties are important if a polymer is used as an insulator, and also if it is used in applications in which heat transfer is desirable. Five sets of virgin and recycled commercial polymers widely used in many applications (including food wrapping) were selected for this study. 

It was found that in several polymers, such as stretched and poled poly(vinylidene fluoride) (PVDF) and its copolymer, poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), a strong polarization effect is observed under influence on mechanical stress and temperature. This means that piezoelectric and pyroelectric gas sensors can also be designed based on polymers (see Chap. 13 [Vol. 1]). 

In the late 19 century, Pierre and Jacques discovered that quartz crystals produced an electric charge when deformed and, conversely, the crystals changed dimension when they were subjected to an electric charge. They named this phenomenon/)/ezoe/ecfr/c/(y. The same effect was observed when quartz crystals were exposed to thermal radiation this effect was called pyroelectricity. Some fluoropolymer crystals exhibit similar behavior, examples of which include polyvi-nylidene fluoride, polyvinyl fluoride, and fluorinated ethylene propylene copolymer. 

S. B. La A. S. DcRcggi. M. G. Broadhurst. and 0. T. Davis, Effects of poling field time on pyroelectric coefficient and polarization uniformity in polyvinyl fluoride, Ferroelectrics 55 119(1981). 

D. De Rossi, A. S. Dc Reggi. M. 0. Broadhunt, E C Roth, and O. T. Davis, Method of evaluating the (bemud stability of the pyroelectric properties of polyvinylidene fluoride Effect of poling tempenuure snd field, J, Appl. Pkys 53 6320 (1982)... 

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