Mechanical applications, ferroelectric polymers

Ferroelectric liquid crystals (FLC) have attracted attention because of their high speed response and memory effect (7-5). The characteristics of fast response and memory effect make them suitable in electro-optical device applications, such as display, light valve and memory devices. Ferroelectric side chain liquid crystalline polymers (FLCPs) exhibit desirable mechanical properties of polymers and electro-optical properties of low molecular weight FLC, which have been investigated extensively Corresponding author. 

PVDF was discovered by Dr. Heiji Kawai in 1969 [32]. Although PVDF is a piezoelectric system, it is a ferroelectric cum piezoelectric material as explained earlier, with a Curie point of 103 °C. PVDF possesses various phases such as a, p, y, and 5, among which p-phase has the most responsive piezoelectric properties. Compared with all ferroelectric polymers, PVDF has a dielectric constant with a reasonable chemical and mechanical durability [4,32]. In general, the physical properties of PVDF make it the most valuable material for application in sensors. 

The rest of this chapter is structured as follows. Section 5.2 gives a brief historical overview together with a description of the synthesis, structure and preparation of ferroelectric polymers. Section 5.3 defines the properties required to evaluate these materials, and includes typical values and brief accounts of the measurement methods. Section 5.4 details the applications of ferroelectric polymers, covering sound transducers, biomedical, pyroelectric and mechanical applications. Conclusions are briefly described in section 5,5. 

The electrical and mechanical properties trf piezoelectric polymers make them a possible alternative to ferroelectric ceramics such as lead zirconate titanate. For several reasons, they are attractive for transducer design. The mechanical flexibility and conformability of thin-film PVDF means that it can be configured into a wide range of transducer products. The low acoustic impedance of PVDF is companrf>le to body tissues, which makes it useful for acoustic imaging applications. Short impulse response and high axial resolution in acoustic imaging systems arc possible with PVDF-featured devices because of the robustness and broadband characteristics of the polymer. 

The electrical and mechanical properties of piezoelectric polymers make them interesting also in the development of electroacustk or ultrasonic transducers for medical applications. Comparison of tbe representative PVDF material characteristics with a convenlional ferroelectric ceramic as PZT shows several features of piezoelectric polymers which make them attractive in transducer design (TU>le 1). 

The huge variety of nanocomposite materials containing versatile nanofillers offers a wide range of potential applications. Depending on the specific properties of the nanofiller, the polymer materials may be reinforced chemical and thermal stability can be enhanced or completely new electrical, ferroelectric, magnetic, or diverse optical properties may be introduced to the material. Since the reinforcement of polymers is taking an immense research field including CNT composite materials and clay nanocomposites, the mechanical properties of these composite materials have been discussed elsewhere extensively. Hierefore, this contribution will focus on optical and thermal properties of nanocomposite and hybrid materials. 

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