Ferroelectric polymers materials

Except these materials, ferroelectric liquid ciystals are another special class of ferroelectric polymer materials. They attracted ranch attention especially because of the application in the hquid ciystal display units. 

Ferroelectric polymer materials like PVDF or its derivatives are mentioned, since they behave as ferroelectric materials (see Fig. 2.2) - They have crystallinity and the crystals show polymorphism by controlling the preparation method. Much detailed work has been carried out on piezoelectric and/or pyroelectric properties, together with their characteristics as electroactive actuators. These materials have long been mentioned as typical electroactive polymers. Through these materials, it is considered that the strain induced in the polymer materials is not large. The electrostrictive coefficient is known to be small for polymers. These are non-ionic polymers and the induced strain originates from the reorientation or the deformation of polarized crystallites in the solid materials. 

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. 

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]. 

Recent advances in PVDF-based materials have led to the elimination of the hysteretic behavior characteristic of ferroelectrics. For this reason, these PVDF-based materials are classified as relaxor ferroelectric polymers they will be discussed under the Electrostrictive Polymers heading. 

Polymer electrets can be operated as sensors or actuators. Their operation is very similar to that of a piezoelectric material and their direct piezoelectric transducer coefficient (d33) is higher than that of solid PVDF ferroelectric polymers [97]. If a compressive force is apphed to the film, the pores will deform preferentially with respect to the polymer material. Unlike charges within the polymer will be pushed closer together and the potential measured at the contacts will change accordingly. Similarly, the application of a voltage across the electrodes will yield a change in thickness in the material. 

Three classes of quadratic NLO polymers have been investigated side chain liquid crystal polymers, ferroelectric polymers and amorphous polymers. Amorphous polymers seem the most promising class of polymeric materials for NLO applications. ... 

We have shown how Electrostatic Force Microscopy can be an extremely useful tool to investigate and to modify the electric properties of sample surfaces on a microscopic and even nanoscopic scale and we have presented a phenomenological model to help relating the experimental data to the material properties. Ferroelectric domains can locally be reoriented and their time evolution can be followed, as was shown for PZT. We have also demonstrated how the ferroelectric polymer PVDF-TrFe could be locally modified which can be used to locally vary the optical properties of a LC cell. Finally, we have demonstrated that rubbing polymer substrates can indeed result in electrostatic charging, in particular for PMMA and PI, while no charging is found for PVA. 

Recently, liquid-crystalline polyphenylene derivatives have been synthesized through substitution of a fluorine-containing chiral liquid-crystalline group into side chains, with an aim to develop ferroelectric liquid-crystalline conjugated polymers (Fig. 5 Suda and Akagi 2008). These are attracting interest because they can afford anisotropies in electrical and optical properties when they are macroscopically aligned. This study also elucidated that PPP can be used to prepare new types of polymer materials. 

Symposium on Advanced Dielectrics, Piezoelectric, Ferroelectric, and Multiferroic Materials Geopolymers and other Inorganic Polymers Materials for Solid State Lighting Advanced Sensor Technology for High-Temperature Applications... 

There are maity other ferroelectric polymer systems under investigation today. Among them following materials should be pointed out for their properties ... 

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