Temperature dependence of microhardness in the 70/30 polyvinylidene fluoride-trifluorethylene copolymer: New structural aspects of the curie transition

Abstract

A combined X-ray diffraction and microhardness investigation of the 70/30 polyvinylidene fluoride-trifluorethylene copolymer was carried out as a function of temperature. The changes in microhardness are interpreted in terms of variations in lattice spacing of the ferro-and paraelectric phases, crystallinity and long period. The changes of microhardness with temperature show four distinct temperature regions. In addition to a low temperature range, in which microhardness decreases exponentially with temperature, the ferroparaelectric Curie transition involves a faster hardness decrease. At higher temperature, the sudden microhardness rise is ascribed primarily to an increase of crystal thickness within the remnant paraelectric phase. Near the melting point, the fusion of thinner crystals leads to a range in which microhardness decreases exponentially again.

Ferroelectricity of polymers based on vinylidene fluoride

“…The smooth changes in the microhardness of this copolymer can be due to the same process. 165 The rearrangement of the polar phase lattice into the lattice of the nonpolar phase might take place at a certain critical concentration of kink bonds (conformational defects) in the ferroelectric crystal. Above the Curie point, the crystals of the paraelectric phase start to grow noticeably and, simultaneously, the degree of crystallinity increases (see Table 10).…”

“…Values of the long period L, the transverse dimension of the crystal lc , the size of amorphous layers la and the degree of crtystallinity a for 70/30 VDF/TrFE films at various temperatures 165. …”