Piezoelectric fluoropolymers

P(VDCN-VAc) has been used in ultrasonic transducers as a thickness extensional (TE) mode resonator. The transducer of piezoelectric fluoropolymers. PVDF and/or P(VDF-TVFE), is well known in medical applications. Ihble 3 lists data on the electromechanical properties of P(VDCN-VAc), P> F. and PZT. Ekctmmechanical coupling frurtor K, of these polymers is 0 J-0 J, which is larger than that of quartz but substantially... 

Curiously, fluorine incorporation can result in property shifts to opposite ends of a performance spectrum. Certainly with reactivity, fluorine compounds occupy two extreme positions, and this is true of some physical properties of fluoropolymers as well. One example depends on the combination of the low electronic polarizability and high dipole moment of the carbon-fluorine bond. At one extreme, some fluoropolymers have the lowest dielectric constants known. At the other, closely related materials are highly capacitive and even piezoelectric. 

Ishii, K, Nagata, K, Osawa, H. Nanba, N. "Piezoelectric Properties in Porous Fluoropolymer Having Isolated Voids",Trans. Inst. Electr. Eng. Jpn., Vol.l29-A, No.5, pp.373-378, (2009) [in Japanese]... 

State of the Art. Pioneering work in the area of piezoelectric polymers (9) led to the development of strong piezoelectric activity in poly(vinylidene fluoride) (PVDF) and its copolymers with trifluoroethylene (TrFE) and tetrafluoroethylene (TFE). These semicrystalline fluoropolymers represent the state of the art in piezoelectric pol5uners and are currently the only commercial piezoelectric polymers. 

Other commercial fluoropolymers (all made by free-radical mechanisms) include polychlorotrifluoroethylene (Kel-F), which is similar to PTFE but which can be moulded at temperatures 300 °C. Polyvinylidene difluoride (PVDF) is a thermoplastic (T 160°C) and films of this material show piezoelectric behaviour. When copolymerized with hexafluropropene a very chemically resistant elastomer is obtained (Viton). Polyvinylfluoride (PVF) is another highly crystalline polymer (T 197°C) which is used for high-performance protective coatings. 

Kawai s (7) pioneering work almost thirty years ago in the area of piezoelectric polymers has led to the development of strong piezoelectric activity in polyvinylidene fluoride (PVDF) and its copolymers with trifluoroethylene and tetrafluoroethylene. These semicrystalline fluoropolymers represent the state of the art in piezoelectric polymers. Research on the morphology (2-5), piezoelectric and pyroelectric properties (6-70), and applications of polyvinylidene fluoride 11-14) are widespread in the literature. More recently Scheinbeim et al. have demonstrated piezoelectric activity in a series of semicrystalline, odd numbered nylons (75-77). When examined relative to their glass transition tenq>erature, these nylons exhibit good piezoelectric properties (dai = 17 pCTN for Nylon 7) but have not been used commercially primarily due to the serious problem of moisture uptake. In order to render them piezoelectric, semicrystalline polymers must have a noncentrosynunetric crystalline phase. In the case of PVDF and nylon, these polar crystals cannot be grown from the melt. The polymer must be mechanically oriented to induce noncentrosynunetric crystals which are subsequently polarized by an electric field. In such systems the amorphous phase supports the crystalline orientation and polarization is stable up to the Curie temperature. 

Melhnger A, Wegener M, Witges W, Gerhard-Multhaupt R (2001) Thermally stable dynamic piezoelectricity in sandwich films of porous and non-porous amorphous fluoropolymer. Appl Phys Lett 79 1852-1854... 

Zhukov S, von Seggem H (2007b) Polarization hysteresis and piezoelectricity in open-porous fluoropolymer sandwiches. J Appl Phys 102 044109 Zhukov S, Fedosov S, von Seggem H (2011) Piezoelectrets from sandwiched porous polytetrafluoroethylene (ePTFE) films influence of porosity and geometry on charging properties. J Phys D Appl Phys 44(10) 105501... 

Janesheski, R.S., Groven, LJ. and Son, S.F. (2011) Fluoropolymer and aluminum piezoelectric reactives, 17th Biennial International Conference... 

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