Vinylidene fluoride dielectric

The equimolar copolymer of ethylene and tetrafluoroethylene is isomeric with poly(vinyhdene fluoride) but has a higher melting point (16,17) and a lower dielectric loss (18,19) (see Fluorine compounds, organic-poly(VINYLIDENE fluoride)). A copolymer with the degree of alternation of about 0.88 was used to study the stmcture (20). Its unit cell was determined by x-ray diffraction. Despite irregularities in the chain stmcture and low crystallinity, a unit cell and stmcture was derived that gave a calculated crystalline density of 1.9 g/cm. The unit cell is befleved to be orthorhombic or monoclinic (a = 0.96 nm, b = 0.925 nm, c = 0.50 nm 7 = 96%. 

The last column of Table 2 lists the values of k calculated from Eq. (103). In the calculation, s at 1 MHz was used and Poisson s ratio m was assumed to be 0.35. Agreement between observed values and calculated ones is fairly good except for poly (vinylidene fluoride) (PVDF) and poly (methyl methacrylate) (PMMA), which exhibit a remarkable dielectric relaxation at room temperature. 

Fig. 25. Ratio of electrostriction constant to dielectric constant of roll-drawn poly(vinylidene fluoride) film (draw-ratio = 2.3) plotted against angle 0 between elongational strain and draw-axis. Drawn after Nakamura and Wada [J. Polymer Sci. A-2,9,161 (1971)] by permission of John Wiley Sons, Inc.

Fig. 28. Piezoelectric stress constant obtained from inverse piezoelectric effect and electrostriction constant of drawn and polarized poly(vinylidene fluoride) film plotted against temperature. Draw ratio = 7. Polarized at 90° C under the field of 400 kV/ctn for 3 hours. Frequency of applied voltage = 37.5 Hz. (Oshiki and Fukada, 1971) Broken line represents dielectric constant at 21.5 Hz for roll-drawn poly (vinylidene fluoride) film (Peterlin and Eiweil, 1969)...

Examples of fluoroplastics include polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), ethylene—chlorotrifluoroethylene (ECTFE), ethylene—tetrafluoroethylene (ETFE), poly(vinylidene fluoride) (PVDF), etc (see Fluorine compounds, organic). These polymers have outstanding electrical properties, such as low power loss and dielectric constant, coupled with very good flame resistance and low smoke emission during fire. Therefore, in spite of their relatively high price, they are used extensively in telecommunication wires, especially for production of plenum cables. Plenum areas provide a convenient, economical way to run electrical wires and cables and to interconnect them throughout nonresidential buildings (14). Development of special flame-retardant low smoke compounds, some based on PVC, have provided lower cost competition to the fluoroplastics for indoors application such as plenum cable, Riser Cables, etc. 

The mechanism of the polarity inversion of tautomeric molecules is totally different from the orientation polarization of conventional organic dielectrics, such as camphor and poly(vinylidene fluoride), and the dielectric response of this new type of dielectric should be much faster. Furthermore, a significant contribution of the proton-tunnelling mechanism to the proton tautomerism is frequently observed. Consequently, the dielectric property derived from proton tautomerization should have a high chance of being related to quantum phenomena. 

Vinylidene fluoride-trifluoroethylene (VF2-F3E) copolymers exhibit a ferroelectric-paraelectric phase transition, the first such case found for a synthetic polymer. In this transition, the electric polarization and piezoelectric constant of the film disappear above the Curie point (Tcurie)- The temperature dependence of the dielectric constant, , obeys the so called Curie-Weiss law ... 

Figure 9.4. Polymers with very large dielectric constants caused by asymmetric fluorination. (a) Poly(vinylidene fluoride), where the fluorine substitution is symmetric at a given C atom, but asymmetric (alternating) along the chain, (b) Poly[oxy(methyl y-trifluoropropylsilylene)].

Vinylidene Fluoride Hexafluoropropylene Copolymer - Thermoplastic copolymer of vinylidene fluoride and hexafluoropropylene. Has better thermal stability, antistick, dielectric, and antifriction properties, and chemical resistance, but lower mechanical strength at room temperature and creep resistance, compared to incompletely fluorinated fluoropolymers. Processing by conventional thermoplastic techniques is difficult due to its high melt viscosity. Uses include chemical apparatus, containers, films, and coatings. Also called TAM... 

Chiu (116) used the apparatus previously described to study the thermal decomposition of selected polymers such as polyethylene terephthalate), po y(vinyl fluoride), po y(vinylidene fluoride), and others. The dielectric constant curves of a group of fluorocarbon polymers are shown in Figure 11.33. As illustrated, the more polar polymers such as poly(vinylidinefiuoride) (PVDF) and poly(vinyl fluoride) (PVF) show characteristic dielectric loss peaks that are distinguishable from the relatively featureless and low-loss curves of the other polymers. For PVF, the low-temperature process is due... 

Miyamoto Y, Miyaji H, Asai K (1980) Anisotropy of dielectric relaxation in crystal form II of poly(vinylidene fluoride). J. Polymer Sci., Polymer Phys. Ed. 18 597... 

Huang C, Klein R, Xia F, Li HF, Zhang QM, Bauer F, Cheng ZY (2004) Poly(vinylidene fluoride-trifluoroethylene) based high performance electroactive polymers. IEEE Trans Dielectr Electr Insul 11 299... 

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... 

Polyvinylidene Fluoride Thermoplastic polymer of vinylidene fluoride has good strength, proeessability, wear, fire, solvent, and creep resistance, and weatherability, but decreased dielectric properties and heat resistance. Processed by injection and transfer molding, extrusion, and powder coating. Used in electrical insulation, pipes, chemical apparatus, coatings, films, containers, and fibers. Also called PVDF. 

CNT-polymer composites at very low nanotube loadings exhibit substantial electrostrictive strains when exposed to an electric field that is dramatically lower than that required by neat polymers. Zhang et al. have shown that the crystallinity. Young s modulus, dielectric constant, electrostrictive strain, and elastic energy density of electrostrictive poly(vinylidene fluoride-trifluor-oethylene-chlorofluoroethylene) P(VDF-TrFE-CFE)] can be simultaneously improved by inclusion of only 0.5 wt% of MWNTs. At an applied electric field of 54 MV m the 0.5 wt% nanocomposite generates a strain of 2%, which nearly doubles that of pure P(VDF-TrFE-CFE) polymer. 

Koga, K. Ohigashi, H. "Piezoelectrisity and related properties of vinylidene fluoride and trifluoroethylene copolymers", J. Appl. Phys., Vol.59, No.6, pp.2142-2150, (1985) Lindner, M., Bauer-Gogonea, S., Bauer, S., Paajanen, M. Raukola, J. "Dielectric barrier microdischarges Mechanism for the charging of cellular piezoelectric polymers", J. Appl. Phys., Vol.91, No.8, pp.5283-5287, (2002)... 

Qin et al. [114] prepared functionalized single-walled carbon nanotubes (SWNTs) through treatment of polystyrene via the grafting-to method. The results showed that the PS was covalently attached to the side walls of SWNTs. The poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was functionalized with glycidyl methacrylate (GMA) via atom transfer-radical polymerization (ATRP) and the BaTiOs nanoparticles were modified by amino-terminated silane molecules. Then, the nanocomposites with high dielectric coti-stant and high thermal conductivity were prepared by a grafting to method [115]. 

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]... 

Poly(vinylidene fluoride), PVDF or PVF2, is usually manufactured from radical initiated batch polymerization process in aqueous emulsion or suspension of CH2=CF2 monomer. PVDF is a thermoplastic that exhibits interesting properties, such as piezoelectric, pyroelectrical, and ferroelectric behaviors. PVDF has even superior dielectric permittivity arising from the strong polymerization originating from C—F bonds, and the spontaneous orientation of dipoles in the crystalline phases makes it a polar polymer with good compatibility with polar chemicals. 

To develop dielectric polymers with C-CN and C-F groups, the syntheses of poly(vinylidene fluoride)-h-poly(AN, MAN, VCN) (PVDF-h-PMcN) block copolymers (Scheme 20.8), using the iodine transfer polymerization (ITP) of acrylonitrile (AN), methacrylonitrile (MAN), and vinylidene cyanide (VCN), in the presence of PVDF-1, was reported. In a first step, the ITP of vinylidene fluoride (or 1,1-difluoroethylene, VDF) with C6F13I initiated by tcrt-butyl peroxypivalate (TBPPI)... 

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