Polyvinylidene Fluoride (PVDF) Phase Transitions under In-Situ High Pressure

Polyvinylidene fluoride (PVDF) is a versatile semi-crystalline polymer exhibiting outstanding piezoelectric, pyroelectric and dielectric properties, and is therefore widely employed in sensors, energy devices and biomedical applications. Its performance is governed by crystallinity and the polymorphic constitutiona (α, β, γ, δ, ε), among which the polar β-phase possesses superior electromechanical characteristics compared with the non-polar α-phase. Nevertheless, the α-phase remains the most stable and the most readily obtained thermodynamical form. The structural evolution of PVDF under high pressure is investigated by means of in situ X-ray diffraction and Fourier-transform infrared spectroscopy. At ambient conditions the powder consists primarily of the α-phase with a minor fraction of β. Upon compression to 0–20 GPa, the α phase gradually diminishes; the emergence of new diffraction peaks and band shifts indicates sequential α→β and β→γ transformations, accompanied by a pronounced increase in β content and concomitant formation of γ. When the pressure exceeds 20 GPa, severe lattice distortion destroys long-range crystalline order, resulting in peak broadening and eventual amorphization. The study unveils the intricate interplay between pressure-induced chain rearrangement and polymorphic transitions, clarifies the high-pressure phase-transformation pathway and structural evolution of PVDF, and thereby deepens the structure–property understanding of this polymer. The findings also provide a theoretical basis for tailoring its performance under extreme conditions and for designing high-pressure technologies.