Ferroelectric critical behavior in the copolymers of vinylidene fluoride and trifluoroethylene from nuclear spin-lattice relaxation studies

An anomalous increase of the reciprocal spin-lattice relaxation time T 1 -1 near the Curie temperature T c (↓) during thecooling process of the vinylidene fluoride (VDF) and trifluoroethylene (TrFE) copolymer was investigated by applying an effective Ising spin model to the configuration fluctuation of the trans segment. The anomalous part of T 1 , ( T 1 ) fluc , of the form A ( T - T 0 ) 1/2 , where T 0 is the characteristic temperature, was derived in terms of the random phase approximation in the Ising model. T c (↓) for the VDF and TrFE copolymer was almost equal to T 0 . By using the observed value of ( T 1 ) fluc , the effective nearest-neighbor distance between fluctuating trans segments and the correlation length were calculated. The contribution of the nearest-neighbor interaction to the polarization fluctuation is discussed for the VDF contents of 52, 65 and 72 mol%.