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-11 and poly(vinylidene fluoride) (PVF 2 ), 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 PVF 2 concentration measured by temperature modulated differential scanning calorimetry (TMDSC). Fourier transform infrared spectroscopy (FTIR) was used to measure the shifts of several characteristic bands of nylon-11 and PVF 2 in the blends, which indicated specific interaction between the polar amide groups (CONH) in nylon-11 and the polar CF 2 groups in PVF 2 . We observed that this interaction affected the crystallization behavior of both components in the blend. The nylon-11 hydrogen-bonded structure became more disordered as the PVF 2 concentration increased in the blend. PVF 2 developed a large proportion of polar crystal phases (I and III) in blends with high nylon-11 concentration instead of nonpolar phase II developed in pure PVF 2 under similar melt quench conditions. In the uniaxial drawing process, the phase transformation of PVF 2 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 PVF 2 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 to160 °C) of piezoelectric properties in the blends, which enable this new polymeric material to be used in many new electroactive applications.