Joint experimental and computational investigation of the structural and spectroscopic properties of poly(vinylidene fluoride) polymorphs.

State-of-the-art density functional theory calculations are here adopted for the investigation of the crystal structure and of the vibrational properties of alpha, beta, gamma and delta phases of poly(vinylidene fluoride) (PVDF), in comparison with IR and Raman measurements. DFT calculations allowed a detailed interpretation of the IR and Raman spectra of alpha and beta phases, giving vibrational assignments useful for qualitative and quantitative characterization of these systems. From a molecular perspective, the computational investigation of the crystal structure and the spectra of PVDF polymorphs helped in clarifying the role of supramolecular dipole-dipole interactions, which indeed modulate the vibrational properties of these systems, indicating also that intermolecular interaction could play a significant role in the modulation of ferroelectric properties. Furthermore, the combined experimental and computational approach allowed us to identify and characterize the thermally and mechanically induced gamma phase, shedding light on the far-IR marker bands of this elusive phase of PVDF.