Multi-scale spectral combined DFT calculation to study the isothermal crystallization dynamics and mechanism of PVDF-CTFE copolymer
摘要
Poly(vinylidene fluoride)-co-chlorotrifluoroethylene (PVDF-CTFE) has attracted significant attention from researchers due to its excellent performance resulting from its crystalline structure. However, there is still a lack of in-depth understanding of the multi-scale, quantitative mechanisms from molecular nucleation to microscopic growth during the isothermal crystallization process of this material. This study innovatively combines density functional theory (DFT), ultrafast scanning calorimetry, and in situ Raman techniques to achieve, for the first time, a comprehensive multi-scale analysis of the crystallization process of PVDF-CTFE (88/12) at 453 K. The DFT calculations not only identified the complete vibrational mode assignments of key Raman characteristic peaks of the copolymer (285, 410, 514, 798, 839, and 879 cm−1), but also revealed the molecular mechanism by which the CTFE unit promotes the formation of the electroactive γ phase. Experimentally, in situ Raman measurements quantitatively captured the crystallization kinetics: The intensity of the C–C stretching vibration (285 cm−1) peaked at 100 s, while the peak at 514 cm−1 rapidly increased within 10 s, clearly indicating that early ordering was quickly completed. Additionally, ultrafast calorimetry showed that crystallization underwent dramatic changes within 10 s, reaching equilibrium after 200 s, with the melting enthalpy showing phased growth. These multi-scale data collectively indicate that the γ phase is the ultimately dominant crystal form, driven by the rapid initial nucleation induced by the CTFE units. This work not only provides a quantitative mechanistic picture of PVDF-CTFE crystallization but also establishes a robust, multi-scale research paradigm, laying a solid foundation for the precise regulation of its crystal form and performance.