Dipolar intermolecular interactions, structural development, and electromechanical properties in ferroelectric polymer blends of nylon-11 and poly(vinylidene fluoride)

A new polymer blend was developed from two well-known ferroelectric polymers, nylon-ii and poly(vinylidene fluoride) (PVF2), by mechanically mixing them in powder form. The intermolecular interactions between these two semicrystalline polymers was evidenced by the observed decrease of the glass transition temperature and melting points of nylon-11 with increasing PVF2 concentration measured by temperature modulated differential scanning calorimetry (TMDSC). Fourier transform infrared spectroscopy (FTIR) was used to measure the shifts of several characteristic hands of nylon-ii and PVF2 in the blends, which indicated specific interaction between the polar amide groups (CONH) in nylon-ii and the polar CF2 groups in PVF2. We observed that this interaction affected the crystallization behavior of both components in the blend. The nylon-ii hydrogen-bonded structure became more disordered as the PVF2 concentration increased in the blend. PVF2 developed a large proportion of polar crystal phases (I and III) in blends with high nylon-ii concentration instead of nonpolar phase II developed in pure PVF2 under similar melt quench conditions. In the uniaxial drawing process, the phase transformation of PVF2 from nonpolar phase II to the most polar phase I crystal form is more complete, and the resulting phase I crystals are more ordered than in pure PVF2 as shown by FTIR and wide-angle X-ray diffraction (WAXD) studies. This structural change led to enhanced piezoelectric response and significantly improved high-temperature stability (up to 160 degrees C) of piezoelectric properties in the blends, which enable this new polymeric material to be used in many new electroactive applications.