Ferroelectricity of polymers based on vinylidene fluoride

Abstract

Characteristics of the ferroelectricity in polyvinylidene fluoride (PVDF) and copolymers based on vinylidene fluoride (VDF) with different previous thermomechanical histories are analysed. Switching of polarisation and the fluctuation mechanism of formation of new nuclei upon the appearance of conformation defects such as kink bonds are considered. The role of the space charge, which stabilises the new polarisation position, is noted. It is shown that the Curie transition can be either a first-or second-order phase transition depending on the copolymer composition. The influence of the morphology of PVDF on some ferroelectric characteristics is found. In particular, the morphology of thick lamellar crystals is favourable for enhanced spontaneous polarisation. It is shown that a ferroelectric structure approaching the texture of an ideal single crystal can be created in Langmuir ± Blodgett films. As the number of unimolecular layers decreases, the concentration of conformational defects in these films increases and the crystallographic order in the lattice is violated. This intensifies the low-temperature Curie transition. The bibliography includes 247 references.

Dielectric relaxation in vinylidene fluoride–hexafluoropropylene copolymers

“…On the other hand, there is a possibility of formation of ferroelectric phase in this class of polymers. 1,2,4 And therefore in the regions of spontaneous polarization order-disorder transitions are observed. 20,21,25,30 Large number of dielectric measurements illustrate that the a c -transition is clearly observed in PVDF crystallized in nonpolar phase, but practically disappears in this polymer in polar b-modification.…”

“…Ferroelectricity 1,2 and high piezo-and pyroactivity in these compounds, along with specific properties of polymers, allow to use them as a material for various energy converters. 3,4 Mechanisms of ferroelectricity and piezoelectricity are still not clearly understood, 2,5,6 particularly the role of molecular mobility in crystalline and especially in the amorphous phase is not clear in these phenomena. Therefore, investigation of mechanisms of molecular dynamics in considered class of polymers is actual.…”

Investigation of ferroelectric domains in thin films of vinylidene fluoride oligomers

“…17 Furthermore, oligomers are amenable to a wider range growth and fabrication methods including epitaxial growth. 14 Structurally, VDF oligomers have different possible terminal functional groups (Q ¼ CH 3 , CF 3 ; R ¼ OH, I, etc.) at the ends of the molecular chains: Q-[CH 2 -CF 2 ] n -R (Fig.…”

“…Polyvinylidene fluoride (PVDF) based ferroelectric materials have been a focus of continuous research activities [1][2][3][4][5] since the discovery of piezo-, [6][7][8] pyro-, 9,10 and ferroelectricity [11][12][13][14] in these fluorinated polymers. In particular, VDF oligomers, which contain a finite number (n) of VDF units, present a unique opportunity to not only fabricate highly ordered crystalline ultra-thin films, but also control their functional properties by varying the orientation and length of molecular chains.…”

A facile method to enhance ferroelectric properties in PVDF nanocomposites

“…Assuming that for an uniaxial ferroelectric the free energy of unpolarized crystals is equal to zero [32][33][34] , the free energy, G, of polarized crystals could be written as:…”