Polarization and orientational order in polymer ferroelectric films based on vinylidene fluoride |
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Authors: | R A Gerasimov A V Maksimov |
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Institution: | 1.Cherepovets State University,Cherepovets, Vologda oblast,Russia |
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Abstract: | Phase transitions and the development of orientational order are studied for three-dimensional polymer systems with the anisotropy
of local intra- and interchain orientational-deformation interactions of chains with the dipole-type potential. In the proposed
model of chains composed of elastically deformed segments with a fixed mean-square length (in the modified model of Gaussian
subchains), there is a certain critical temperature at which the second-order phase transition from the isotropic state to
the orientationally ordered state occurs. The temperature dependences of the parameter of the dipole order for thick films
are calculated, and these dependences are compared with the corresponding dependences within the mean-field approximation
according to the Ising model for ferromagnetics and within the Langevin continuum model for ferroelectric materials as well
as with the experimental data on the thermal depolarization in the films based on the vinylidene fluoride-trifluoroethylene
copolymer. The order parameter is calculated as a function of the film thickness (the length of chains) under certain boundary
conditions imposed on film ends, and the calculated values are compared with the values predicted by the phenomenological
theory and with the experimental data on the polarization distribution in the ferroelectric films based on vinylidene fluoride. |
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