Polymeric electrets

A spectacular relaxation phenomenon of polymeric materials is exhibited in a field-temperature treatment phenomenon. As was shown above, the polarisation of a polymeric material after application of an electric field increases after an instantaneous polarisation to the relaxed polarisation. If the electric field is subsequently released the polarisation decreases again with time. However, if the polarisation took place at a temperature above the glass transition temperature after which the temperature was decreased to a temperature well below Tg, then depolarisation is not possible, due to the immobilisation of the polymer molecules. In this way a so-called electret maybe formed, the electric counterpart of a magnet. 

Attempts to develop polymeric electrets with negatively charged surfaces which are more compatible with blood. 

PPE exhibits a high dielectric strength. Thus, it can be used as a polymeric electret. Neat PPE shows an excellent charge storage behavior, which is better than that of cellular poly(propylene) and polyfether imide). 

Electret is an important cross-scientific subject of dielectric physics, material science, sensor engineering, medical and bio-engineering (Sessler G., Sessler et al., Nalwa H., Goel M.)-Over the years, considerable interest has been shown in the surface potential decay of corona-charged polymeric materials. Besides the electrets material and conditions of producing electrets the surface potential decay depends on number of factors under which the electrets have been stored or used, for example temperature, humidity, pressure etc. (Zhongfu et al, Gang-Jin et al., Ribeiro et al.). 

The polymeric materials are utilized in industry and an ordinary household with the characteristic that a natural organic material does not have. Research and development are performed actively now because the polymers are materials with a variety of functionality (Imai et al., 2002 Ishii et al., 2009 Ishimoto et al., 2009 Varlow Li, 2002). By such a background, we aimed at the polymer system piezoelectric material which let it give piezoelectricity as the sensor function. For typical piezoelectric material(Koga Ohigashi,1985 Lindner etal.,2002), PZT and BaTiCb are well known until now. In contract, the PVDF of the polymer system piezoelectric material immobilized CF2 dipolar orientation. Piezoelectric modulus d.33 of the pwrous polymer electrets is higher than PVDF, and in a polymer system, polaristation reversal happens. 

In this context, the possibility to tune tire piezo- and pyroelectricity of specific composites (Floss et al. 2000) by means of separate poling of the inorganic particles and of the polymer crystallites should also be mentioned. In addition, piezo-, pyro-, and ferroelectric polymers such as PVDF and its relevant copolymers may be optimized by controlling fire poling of the amorphous and of the crystalline phase, as well as of the interface between fiiem (Maxwell-Wagner interface polarization) separately (Rollik et al. 1999). Furthermore, it is possible to follow the examples of the classical electret transducers (witti polymeric space-charge electrets) or of the dielectric-elastomer transducers (sometimes also called electro-electrets) and to... 

NonUnearities play essential roles not only in the poling of electrets and ferroeleciric materials (hysteresis, etc.) but also in their piezoelectric and electrostrictive behavior. In addition, piezoelectricity and electrostriction also lead to nonlinearities in the dielectric response of the respective materials (for a general introduction, see Richert (2010)). Consequently, the pressure dependence and the nonlinearities of the dielectric response have been foci of attention in the area of piezoelectricity and electrostriction in inorganic (Zhang et al. 1988) and polymeric (Furukawa et al. 1987 Bauer et al. 2005) dielectrics. Nonlinear effects are also particularly important at large electric fields or deformations (see, e.g., the recent review on the deformation of soft dielectrics (Zhao and Wang 2014) and refs, therein). 

Hattori T, Takahashi T et al (1996) Piezoelectric and ferroelectric properties of polyurea-5 thin films prepared by v or deposition polymerization. J Appl Phys 79 1713 Heaviside O (1885) Electromagnetic induction and its propagation, electrization and electrification. Natural electrets. Electrician 230-231... 

The successful development and optimization of EAPs requires quick, reliable, and precise characterization techniques for all relevant materials and device properties. This chapter gives a concise overview about specific techniques for the characterization of mechanical, electrical, and electromechanical properties of polymeric electrets with some emphasis on ferroelectrets. 

The present chapter provided, on an introductory level, a representative description of experimental methods for the characterization of the mechanical, electrical, and electromechanical properties of polymeric electrets. For obvious reasons, not all experimental approaches could be addressed. A couple of standard techniques for measuring electret properties such as thermally stimulated discharge (TSD)... 

Of the various types of electrets, thermoekctreti ate most important bom the scientific and application points of view. Therefore, most studies have been carried out on ther moelcctrets prepared bom polymeric nutcrials. 

When an electret is reheated at a linear rate, a discharge current te produced in the external circuit This ibermally stimulated discharge current is recorded as a function of temperature. The resulting TSD spectrum shows maxima which corresponds to various decay processes. In polymer electrets, these decay modes correspond to various polymeric relaxations. Therefore, analysis of TSD spectra of polymer electrets provides very useful information on various aspects of charge storage mechanisms and relaxation processes. 

According to some workers [142-145], becomes comparable to Pm. The distinction between the two processes may be made by using different electrodes because S-R emission is electrode dependent whereas the P-F effect is not (155). These two effects arc important for understanding the electret effect in pure and doped polymeric systems (136-142). 

Ihbic 1 shows some of the important polymeric materials that have been used to study the electret effect and their applicatioM in devices [110). 

In previous papers (9,31-33) we have investigated the dielectric and electret properties of the composite pdy(methyl methacrylate) (PMMAVBaTiO, ceramic system. The 0-3 type composites used in the studies were prepared by polymerization of methyl methacrylate (MMA) in which fine particles of ferroelectric ceramics BaHO, were dispersed. The BaTiOt ceramics were ofarained by the known method of triple sintering of BaCO) and TK), in stoichioaietiic ratio. The final process was conducted at about 1620 K for 3 h. resulting in a ceramic density of 5.57 X 10 kg/m This was pulverized and sifted... 

Singh TB, Marjtmovic N, Matt GJ, Saticiftci NS, Schwodiauer R, Bauer S (2004) Nonvolatile oiganic field-effect transistor memory element with a polymeric gate electret. Appl Phys Lett 85 5409-5411... 

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