Ferroelectric polymer blends: Odd-numbered nylon, vinylidene fluoride homopolymer and copolymer with trifluoroethylene

A new polymeric material was developed with significantly improved ferroelectric, piezoelectric properties and improved high temperature stability of the electroactivity compared to any known polymer. It is based on the blends of two well-known classes of ferroelectric polymers: odd-numbered nylon, vinylidene fluoride homopolymer and its copolymer with trifluoroethylene, specifically, Nylon 11, PVF2 and (VF2/VF3) (80/20 mol%) Copolymer.;The intermolecular interactions between Nylon11 and PVF2 and the structural development in the blends were first investigated. The IR band shifts of nylon11 and PVF2 indicate dipolar intermolecular interactions. The crystallization rate of PVF2 increases while Nylon 11 decreases. The increase of Avrami exponent for PVF2 indicates its larger crystal growth dimensions possibly due to the decrease of viscosity and chain entanglements. The crystallinity of PVF2 increases while nylon11 decreases at low nylon concentration. IR band shifts indicates disordered nylon11 hydrogen bonded structure. At high nylon11 concentration region, PVF2 developed a large proportion of polar crystal phases at melt quenching. PVF2 phase transformation from non-polar phase II to most polar phase I upon stretching is more complete and the resulting phase I crystal is more ordered.;The ferroelectric properties of the blends were investigated. The remnant polarization Pr varies with composition and 70% larger than that of either component at 50/50 (by weight), where Pr reached a maximum of approximately 90mC/m2. So did the coercive field E c. Pr (Ec) increases (decreases) with draw ratio. In blends, Pr increases with annealing temperature till 140°C where it is 114mC/m2, indicating that the internal electric field distribution improves the poling of nylon11 due to its relative low dielectric constant.;An enhancement in piezoelectric response at low nylon11 concentration was achieved. The high temperature stability of piezoelectric properties was significantly improved (up to 160°C) at certain composition region. The effect of draw ratio, temperature and frequency on piezoelectric properties of the blends were investigated to reveal some aspects of the structural origin of piezoelectric properties in the blends, as well as the interfacial polarization.;In a comparison study, nylon11/(VF2/VF3)(80/20mol%) Copolymer blend was developed. Pr varied with composition and exhibited a maximum of about 75mC/m2 at a 50/50 (by weight) composition, which is 100% larger than that of (VF2/VF3) Copolymer and 50% larger than that of nylon 11. Ec also exhibited a maximum at this composition. Both Pr and Ec change significantly with draw ratio as in nylon 11/PVF2 blend. At low nylon 11 concentration, an enhancement in piezoelectric strain d31 and stress coefficients e31 was observed. Most of the observed ferroelectric and piezoelectric properties are very similar for these two blend systems as explained by the similar IR band shifts, hence the similar dipolar interaction and possible similar structural development in two blend systems.