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).
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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