Ferroelectric Polarization in Polymers.

A cooperative model has been developed to describe ferroelectric polarization in polyvinylidene fluoride PVDF. The molecular dipoles within the crystal are assumed to have two or more orientations available to them and the lattice energy of a given orientational site is assumed to be proportional to the fraction of molecules having that orientation. An analytical solution is given for the 2-site model which predicts polarization hysteresis typical of ferroelectrics. However, a more complex 6-site model, which can be analysed numerically, is needed to account for observed infra red hysteresis data and electric-field-induced x-ray structural changes which have been reported for PVDF. Although the model is simple, rather complex behavior is observed including a gradual increase or decrease in the remnant polarization with number of cycles of electric field application. Though the agreements with various experimental data are good an obvious need to include kinetic effects in the model is indicated. Author