HIGH-TEMPERATURE CHARACTERISTICS OF NYLON-11 AND NYLON-7 PIEZOELECTRICS

The piezoelectric strain constant, d31, stress constant, e31, and electromechanical coupling coefficient, k31, of Nylon-11 and Nylon-7 films were measured up to a temperature close to their melting points. They were found to exhibit their highest values and, in addition, excellent thermal stability at temperatures between 100 and 200-degrees-C. Maximum stable values were d31 = 14 pC/N and e31 = 21 mC/m2 for Nylon-11, and d31 = 17 pC/N and e31 = 27 mC/m2 for Nylon-7. Corresponding values of k31 were 0.049 and 0.054. Poled and then annealed Nylon samples exhibited little decay of these values even after annealing at 185 and 200-degrees-C for Nylon-11 and Nylon-7, respectively, while poly(vinylidene fluoride) samples showed a large decay in response, decreasing to d31 = 4.9 pC/N, e31 = 11 mC/m2, and k31 = 0.019 after annealing at 175-degrees-C. The extraordinary stability of the piezoelectric activity of these Nylon samples was considered to be related to ferroelectric reorientation of the amide group dipoles followed by closer packing of the hydrogen-bonded sheet structure in the crystalline regions after the annealing treatment.