The theory and its simulation of ferroelectric phase transition of VDF/TrFE copolymers

We present a theoretical study to explain the ferroelectric phase transition of polymers which has been experimentally observed in copolymers of vinylidene fluoride and trifluoroethylene. The phase transition of these copolymers changes its thermodynamic character from a first order phase transition to a diffuse transition with a decrease in a mole fraction of vinylidene fluoride. This fact has been confirmed experimentally by observing temperature hystereses seen as differences between transition temperatures in the heating process and cooling one. The ferroelectric spontaneous polarization of this polymer is formed by a cooperative orientation of dipoles belonging mainly to a vinylidene fluoride part in linear chains with a planar zigzag conformation. In order to represent these interesting ferroelectric phenomena, we examine a three-states model whose element can take three values of the dipole moment as +u, -u, 0. Monte Carlo simulation of this model reveals the physical essence of the ferroelectric characters described above.