Simulations of ferroelectric polymer film polarization: The role of dipole interactions

Abstract

We present a systematic study of the dipole alignment in the polyvinylidene fluoride (PVDF) films using first-principles total energy calculations. The ground state of a single layer film is a state with all the dipoles lying parallel to the film plane. This can also be explained by a dipole-dipole interaction model. The induced mirror charges on conducting substrates or substrates with a non-negligible dielectric response play an important role in aligning the polarization perpendicular to the film. From fitting the ab initio calculations, we obtain an effective monomer dipole moment of $4.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}30}\phantom{\rule{0.3em}{0ex}}\mathrm{C}\phantom{\rule{0.3em}{0ex}}\mathrm{m}$. This corresponds to a spontaneous polarization of $0.087\phantom{\rule{0.3em}{0ex}}\mathrm{C}∕{\mathrm{m}}^{2}$, which agrees with other theoretical and experimental values. Simulation reveals a more complex behavior for molecular bilayer. We studied three molecular multilayer structures to compare the total energy and model calculations. Close examination of these results provides a better understanding of PVDF film growth and dipole orientation on different substrates.