Polymers ferroelectric

Ferroelectric—polymer composite devices have been developed for large-area transducers, active noise control, and medical imaging appHcations. North American Philips, Hewlett-Packard, and Toshiba make composite medical imaging probes for in-house use. Krautkramer Branson Co. produces the same purpose composite transducer for the open market. NTK Technical Ceramics and Mitsubishi Petrochemical market ferroelectric—polymer composite materials (108) for various device appHcations, such as a towed array hydrophone and robotic use. Whereas the composite market is growing with the invention of new devices, total unit volume and doUar amounts are small compared to the ferroelectric capacitor and ferroelectric—piezoelectric ceramic markets (see Medical imaging technology). 

Materials. For holographic information storage, materials are required which alter their index of refraction locally by spotwise illumination with light. Suitable are photorefractive inorganic crystals, eg, LiNbO, BaTiO, LiTaO, and Bq2 i02Q. Also suitable are photorefractive ferroelectric polymers like poly(vinyhdene fluoride-i o-trifluorethylene) (PVDF/TFE). Preferably transparent polymers are used which contain approximately 10% of monomeric material (so-called photopolymers, photothermoplasts). These polymers additionally contain different initiators, photoinitiators, and photosensitizers. 

The piezoelectric polymer investigations give new physical insight into the nature of the physical process in this class of ferroelectric polymers. The strong nonlinearities in polarization with stress are apparently more a representation of nonlinear compressibility than nonlinear electrical effects. Piezoelectric polarization appears to be linear with stress to volume compressions of tens of percent. The combination of past work on PVDF and future work on copolymers, that have quite different physical features promises to provide an unusually detailed study of such polymers under very large compression. 

WangTT, Herbert JM, Glass AM (1987) The applications of ferroelectric polymers. Blackie, Glasgow... 

Note 2 Poly(vinylidene fluoride) after being subjected to a corona discharge is an example of a ferroelectric polymer. 

Ferroelectric substances such as LiNb03 or BaTi03 were found to show anomalous photovoltaic effects (APV) of the order of 103-5 V83). A thin film of a ferroelectric polymer such as PVDF also was found to show APV effects84). Voc of 2.5 x 104 V and short circuit current (Isc) of the order of nA/cm2 were reported. Although the output is very small up to now1, it could be noticed as a specific photoeffect of a thin polymer film. 

Photovoltaic volume effects have been investigated for the ferroelectric polymer-poly vinylidene fluoride [84,85]. The photovoltage was of the order 4 x 104 V for open circuit. The addition of dyes shifts the photosensitivity to the longer wavelength. 

Poly(vinylidene fluoride) with the sequence (CF2-CH2)n is a well known ferroelectric polymer in the crystalline state where the chains adopt an all-trans conformation [424]. This structure could provide interesting properties if used as building block of LC. 

Ferroelectric Polymers Chemistry, Physics, and Applications, edited by Hari Singh Nalwa... 

Chien and Cada [42] have prepared optically active and photoactive SCLC copolymers, 15, with the 4-alkoxyphenyl-4 -alkoxycinnamate chromophore, with the intention of creating LC polysiloxane networks that could be used to prepare macroscopically oriented organic ferroelectric polymers for electro-optical devices. Optical activity was introduced into the polymer by the use of a chiral spacer. Those copolymers which were mesogenic exhibited properties characteristic of a Sc. phase. UV-irradiation of thin films of the polymers in their mesomorphic states at 90°C, led to a loss of the IR absorption at 1635 cm-1 that is due to the cinnamate double bond, and to cross-linking. Long-term irradiation led to... 

Polarising Small Domains in Ferroelectric Polymer Films. 192... 

Considerable interest also has been directed at the use of multicomponent composites where, in theory, the most useful properties from each phase can be realized in the whole. This includes metallodielectric structures where a metallic phase imparts, for example, a high index or more exotic effect (e.g., plasmon resonance) and a low-loss or property-tunable dielectric phase. The dielectric phase can be ceramic or polymeric and also has included ferroelectric polymers, embedded nanoparticles, and organic/inorganic hybrids. ... 

Xu, T., Cheng, Z., Zhang, Q. et al.. Fabrication and characterization of three-dimensional periodic ferroelectric polymer-silica opal composites and inverse opals, J. Appl. Phys., 88, 405, 2000. 

T. Ikeda, O. Zushi, T. Sasaki, K. Ichimura, H. Takezoe, A. Fukuda, and K. A. W. Skarp, Photochemical control of switching behaviors of ferroelectric polymer liquid crystals Poly[2-methylbutyl4 -(l(0-acryloyloxydecyloxy)-biphenyl-4-carboxylate)], Mol. Cryst. Liq. Cryst. 225, 67-79 (1993). 

MAJOR PRODUCT APPLICATIONS thermistors, capacitors, optics, ferroelectric ceramics, filler for ferroelectric polymers, pyro and piezoelectric composites... 

An actual example of an extended application with technological potential is the organic and non-volatile memory, based on an OFET. The main advantage of a non-volatile memory is that its information is maintained during the readout procedure (non-destructive readout, NDRO). A ferroelectric polymer is introduced as a dielectric layer in the OFET. Due to the ferroelectric alignment of dipoles the threshold voltage of the transistor is affected by their dipole moments and can be used as stored information. 

H.S. Nalwa, (ed.) Ferroelectric Polymers Chemistry, Physics and Application, Marcel Dekker, New York, 1995. 

EAPs can be broadly divided into two categories based on their method of actuation ionic and field-activated. Further subdivision based on their actuation mechanism and the type of material involved is also possible. Ionic polymer-metal composites, ionic gels, carbon nanotubes, and conductive polymers fall under the ionic classification. Ferroelectric polymers, polymer electrets, electrostrictive polymers, and dielectric elastomers fall under the electronic classification. 

Fig. 1.4 The alpha and beta phases of the ferroelectric polymer PVDF. The beta phase is stable at room temperature but can be reversibly changed to the alpha phase by heating above the Curie temperature. Above the Curie temperature, an electric field can be used to induce a change between the alpha and beta phases. For ferroelectric relaxor polymers, the Curie temperature is below room temperature so the alpha phase is stable. A change to the beta phase can be induced by an electric field [7], Materials Today 2007, reprinted with permission...

These materials have shown piezoelectric responses after appropriate poling [18]. Their piezoelectric actuation properties are typically worse than ceramic piezoelectric crystals however, they have the advantages of being lightweight, flexible, easily formed, and not brittle. Additionally, while ceramics are limited to strains on the order of 0.1%, ferroelectric polymers are capable of strains of 10% [91] and very high electromechanical coupling efficiencies [93]. 

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