Abstract
Abstract : The piezoelectric strain constant, d31, stress constant, e31, and the electromechanical coupling coefficients, 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 C and 200 C. Maximum stable values were d312= 14pC/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 0.49 and 0.54. Poled and then annealed Nylon samples exhibit little decay of these values even after annealing at 185 C and 200 C for Nylon-11 and Nylon-7, respectively while poly(vinylidene fluoride) samples showed a large decay in response, decreasing to 4.9 pC/N, 11 mC/m, and k = 0.019 after annealing at 175 deg. C. The extraordinary stability of the piezoelectric activity of these Nylon samples was considered to be related to ferroelectric reorientation of the amide groups dipoles followed by closer packing of the hydrogen bonded sheet structure in the crystalline regions after the annealing treatment.
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