Monte Carlo Simulation of a Model System for Ferroelectric Phase Transition in Polymers

A model for ferroelectric phase transitions in copolymers of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) has been examined using Monte Carlo (MC) simulation. The model assumes simple three-states which reflect structural variation of polymers in addition to the directional degrees of freedom of dipoles attached to molecular segments. Results of the simulation qualitatively supported theoretical interpretations obtained by the Bethe approximation of the model. Furthermore, microscopic details of the phase transition were revealed. Temperature dependences of spontaneous polarization and specific heat exhibit clearly a change in a thermodynamic order of the phase transition. The phase transition is classified by a ratio n of intramolecular interaction to intermolecular interaction. The specific heat of the system becomes the maximum at the ratio n where the temperature hysteresis of the phase transition vanishes. It shows that the phase transition is changed from the first order transition to the diffuse one through the critical second order phase transition. In addition, the transformation mechanisms are predicted. The system exhibiting the first order phase transition is transformed due to nucleation and growth. The system doing the diffuse transition is transformed due to spinodal decomposition.