The effect of interlayer interactions on the ferroelectric–paraelectric phase transition inmultilayered thin films of vinylidene fluoride–trifluoroethylene copolymers

Abstract

The interaction between ferroelectric polymer films with different transition temperaturesis evident in the effect of layer thickness on the ferroelectric–paraelectric phase transition inmultilayer films, as revealed by x-ray diffraction and dielectric measurements. Themultilayer samples consisted of alternating Langmuir–Blodgett (LB) films of twodifferent copolymers of vinylidene fluoride with trifluoroethylene, one with 80%vinylidene fluoride and a ferroelectric–paraelectric transition temperature on heating of133 ± 4 °C and the other with 50% vinylidene fluoride and a transition temperature of70 ± 4 °C. Samples with a repeat period of 20 LB layers (10 contiguous layers of each composition)exhibited two distinct phase transitions, indicative of minimal interaction between the twomaterials. Films with a repeat period of 2, or films made from an equal mixture of the twocopolymers, exhibited composite behaviour, with an intermediate transition temperatureand suppression of the transitions associated with the individual compositions. Films witha repeat period of 10 exhibit cross-over behaviour. These results imply that the ferroelectricinteraction length along the (110) direction, which is perpendicular to the film plane, isapproximately 11 nm.