**Temperature dependent structural, elastic, and polar properties of
ferroelectric polyvinylidene fluoride (PVDF) and trifluoroethylene
(TrFE) copolymers**

FC Sun and AM Dongare and AD Asandei and SP Alpay and S Nakhmanson, JOURNAL OF MATERIALS CHEMISTRY C, 3, 8389-8396 (2015).

DOI: 10.1039/c5tc01224d

We use molecular dynamics to calculate the structural, elastic, and
polar properties of crystalline ferroelectric beta-poly(vinylidene
fluoride), PVDF (-CH2-CF2-)(n) with randomized trifluoroethylene TrFE
(-CHF-CF2-)(n) as a function of TrFE content (0-50%) in the temperature
range of 0-400 K. There is a very good agreement between the
experimentally obtained and the computed values of the lattice
parameters, thermal expansion coefficients, elastic constants,
polarization, and pyroelectric coefficients. A continuous decrease in
Young's modulus with increasing TrFE content was observed and attributed
to the increased intramolecular and intermolecular repulsive
interactions between fluorine atoms. The computed polarization displayed
a similar trend, with the room temperature spontaneous polarization
decreasing by 44% from 13.8 mu C cm(-2) (pure PVDF) to 7.7 mu C cm(-2)
**50/50 poly(VDF-co-TrFE)**. Our results show that molecular dynamics can
be used as a practical tool to predict the mechanical and polarization-
related behavior of ferroelectric poly(VDF-co-TrFE). Such an atomistic
model can thus serve as a guide for practical applications of this
important multifunctional polymer.

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