PVDF Polymer and Its Blends with TrFE

Property Biaxially oriented film Uniaxially oriented film [Pg.164]

Poled PVDF films show fenoelectiic behavior clearly demonstrating the polarization reversal in the dielectric Itysteresis curve (Nalwa 1995). Locally created domains ate reported (Giithner and Dransfeld 1992) in scanning force microscopy observations in PVDF. Typical values of the spontaneous polarization are 8-10 X 10 Ccm and of the coercive field 50-100 kVmm . For the material properties see Table 7.17. Uniaxially drawn films are much mote anisotropic in piezoelectric properties. The piezoelectric coefficients are higher than e.g. for quartz crystals, but lower than for PZT ceramics. It is highly desirable to improve the piezoelectric coefficients for the possible applications of polymers. [Pg.164]

PVDF polymer is used in copolymers with TrFE in certain range of its molar ratio. This procedure will increase crystallinity ratio of the polymer up to 90%. Therefore such copolymers exhibit much stronger piezoelectric activity. The most interesting molar ratio range is 60-80% of PVDF. In that range the thickness electromechanical coupling factor kt reaches its maximum value k is a measure for the electromechanical energy conversion). Copolymerized TrFE units decrease the Curie temperature of the polymer (e.g. c = 80°C for P(60%VDF/40%TrFE) polymer). [Pg.164]

First ferroelectric polymer - polyvinilidene fluoride (PVDF or PVF2) - was discovered in 1969. Extensive research has been focused on this substance and their copolymers withtrilluoroethylene (TrFE) since that time. Due to its resistivity to the harmful chemical substances is this polymer used in stractural coatings to prevent damage. Another excellent functional property is a veiy low value of the acoustic impedance, which allows for the better acoustic matching to water environment. Due to this property P(VDF/TrFE) copolymer is being applied mostly in hydrophones (Nalwa 1995) and ultrasound imaging transducers. PVDF polymer and its blends with TrFE are commercially available in the market. [Pg.162]

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