Thermal properties ferroelectric polymers

A copolymer of vinylidene fluoride-trifluoroethylene (VDF/TrFE) copolymer is well known as the polymer for which a clear Curie point was found for the first time in an organic material. At this Curie point, the polymer undergoes a solid-to-solid phase transition from paraelectric to ferroelectric phases with decreasing temperature. Therefore, the changes in the physical properties such as crystal structure, electrical and thermal properties upon the ferroelectric phase transition have drawn many researchers interest. Here, the results concerning the ultrasomc spectroscopic mvestigation on acoustic and viscoelastic behaviour around the ferroelectric phase transition region of this copolymer are described [15]... 

S. and K. tmura. Liquid crystalline arid ferroelectric properties of tartrate with two chiral centers, Chem Lea, 2217 (1969) Thermal and ferroelectric properties of dural liquid crystalline potytartralc, Chem Lea, 1031 (1990) Ferroelectric liquid rystalline po-lytartrate. Polymer J. 23 1483 (1991). 

Ferroelectric polymers are characterized by a range of electrical, thermal and mechanical properties. This section begins with a brief description of the characteristics unique to ferroelectric materials before detailing the... 

Short Review on the Crystalline Structure, Thermal Properties and Morphology of Bulk Ferroelectric Polymers... 

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. 

PVDF is mainly obtained by radical polymerisation of 1,1-difluoroethylene head to tail is the preferred mode of linking between the monomer units, but according to the polymerisation conditions, head to head or tail to tail links may appear. The inversion percentage, which depends upon the polymerisation temperature (3.5% at 20°C, around 6% at 140°C), can be quantified by F or C NMR spectroscopy [30] or FTIR spectroscopy [31], and affects the crystallinity of the polymer and its physical properties. The latter have been extensively summarised by Lovinger [30]. Upon recrystallisation from the melted state, PVDF features a spherulitic structure with a crystalline phase representing 50% of the whole material [32]. Four different crystalline phases (a, jS, y, S) may be identified, but the a phase is the most common as it is the most stable from a thermodynamic point of view. Its helical structure is composed of two antiparallel chains. The other phases may be obtained, as shown by the conversion diagram (Fig. 7), by applying a mechanical or thermal stress or an electrical polarisation. The / phase owns ferroelectric, piezoelectric and pyroelectric properties. 

To summarize the ferroelectric and piezoelectric properties of the discussed polymers, some important ferroelectric and piezoelectric parameters are tabulated in Table 4. As discussed in the previous sections, the ferroelectric and piezoelectric properties of polymeric and polymeric composite systems depend on various factors, such as crystallinity, pohng conditions, glass transition temperature, and before and after electrical poling treatments (electrical, mechanical, and thermal treatments). In addition to the factors mentioned above, for composite systems, laminates or blends, fraction of constituents, and interfacial polarization are also important. Therefore, the... 

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