TEMPERATURE-DEPENDENCE OF MICROHARDNESS AND STRUCTURE OF FERROELECTRIC COPOLYMERS OF VINYLIDENE FLUORIDE

Measurement of the microhardness (H) and X-ray investigation of melt-crystallized random copolymers of vinylidene fluoride with trifluorethylene containing 60 to 80 mol % VF2 were carried out as a function of temperature. The results show that (i) at a given temperature H rapidly increases with VF2 content; (ii) the Curie transition was found to involve an inflection point in the exponential temperature dependence of hardness; and (iii) at the Curie temperature (T(c)) the ferroelectric crystals undergo reversibly a solid-state transformation, followed by the microhardness, to a non-polar (paraelectric) state showing a faster hardness decrease with increasing temperature above T(c). Changes in H with VF2 content and temperature are discussed in the light of the lattice spacings of the ferro- and paraelectric phases and crystallinity values. The application of a relationship to account for correlations between mechanical properties and microstructure is considered.