Deciphering TrFE Fingerprints in P(VDF-TrFE) by Raman Spectroscopy: Defect Quantification and Morphotropic Phase Boundary

Abstract

The electroactive behavior of PVDF-based polymers is strongly related to the macromolecular sequence, chain conformation, and crystallinity. Although β-PVDF is the most attractive phase for applications in organic electronics, PVDF tends to crystallize into other thermodynamically more stable phases. Copolymerization of VDF and TrFE addressed this issue and has resulted in copolymers with high ferroelectric content. Later, the insertion of CFE/CTFE units into the P(VDF-TrFE) architecture yielded terpolymers with relaxor-ferroelectric properties, especially attractive in energy storage and electrocaloric applications. The investigation of the corresponding electroactive phases in these polymers relied mainly on Fourier transform infrared and X-ray diffraction techniques, demanding an extensive combination of material characterization and analysis to detect the crystalline phase distribution and predict the material behavior. In this work, we demonstrate a facile and noninvasive approach to assess the relative ratio of defects in TrFE segments through a detailed analysis of the polymer Raman spectra. By varying the content of TrFE in P(VDF-TrFE) samples, a detailed assignation of the TrFE unit modes (1347 and 1366 cm −1 ) contribution to the polymer Raman spectra was established, which was further validated by Fourier transform infrared spectroscopy, X-ray diffraction, calorimetry, and dielectric spectroscopy measurements. Based on our findings, we further propose a defect quantification ratio that can be used to predict chain conformation and electroactive behavior.