FTIR study on molecular orientation and ferroelectric phase transition in vacuum-evaporated and solution-cast thin films of vinylidene fluoride—trifluoroethylene copolymers: Effects of heat treatment and high-voltage poling

The three-dimensional reorientation behavior of CF2 groups and molecular chains has been investigated by an organized combination of Fourier-transform infrared reflection-absorption (FTIR-RAS) and transmission (TRS) spectroscopic techniques for vacuum-evaporated and the solution-cast thin films of vinylidene fluoride—trifluoroethylene copolymers subjected to annealing and/or high-voltage poling treatments. At an early stage of the vacuum-evaporation, the molecular chains were found to stand almost vertically along the normal to the substrate surface. With increasing evaporation time, the molecular chains were found to tend to deposit with the chain axes almost parallel to the surface. But annealing above the melting point induced a large structural change of chain direction from a parallel to a vertical orientation against the surface plane. Poling on the solution-cast films was found to induce the reorientation of the CF2 groups along the external electric field with the chain axis kept in the original direction.