Recent advances in ferroelectric polymers

Abstract

AbstractIn the Polymer Electroprocessing Laboratory at Rutgers University, we have discovered that the odd‐numbered nylons constitute the second known class of ferroelectric polymers1–3, and that polarized films exhibit piezoelectric properties similar to poly(vinylidene fluoride) (PVF2) and copolymers of PVF2 and trifluoroethylene (PVF2/PVF3). A study of a series of these polymers including nylon 11, nylon 9, nylon 7 and nylon 5 showed that the remanent polarization produced in quenched, cold‐drawn films was a linear function of polymer dipole density4. The highest remanent polarization produced was that of nylon 5, the value attained (P1=125mC/m2) being approximately 2.5 times that of PVF2. We also discovered that (unlike PVF2 or PVF2/PVF3) the remanent polarization could be stabilized to elevated temperatures (close to the polymer melting point). For nylon 5, the remanent polarization and piezoelectric response was stable to over 250°C5. We showed that the hydrogen‐bonded sheet structure in nylon 11 for quenched cold‐drawn films was parallel to the plane of the film, and that after application of high electric fields the hydrogen‐bonded sheet structure was rotated 90° to an orientation perpendicular to the plane of the film3.A detailed X‐ray diffraction study of the effects of humidity and electroprocessing on the switching behavior of nylon 5, nylon 7 and nylon 11 films was carried out5. The piezoelectric and pyroelectric response6 of these films was also determined. The different switching mechanisms observed and the measured piezoelectric and pyroelectric properties will be presented and discussed.