Synergistic Flow Field and Ion-Dipole Interactions Enable γ-β Phase Transformation in Poly(vinylidene fluoride)

Poly(vinylidene fluoride) (PVDF) exhibits excellent piezoelectric properties governed by the content and orientation of its polar phases. Herein, a synergistic regulation strategy integrating a flow field induced by a designed solid-phase extrusion die and ion-dipole interactions introduced by CTAB is established to achieve highly oriented β phase in PVDF. The incorporation of CTAB promotes the formation of the γ phase before extrusion, providing a structurally favorable precursor for the subsequent flow-induced γ-β phase transformation. During solid-phase extrusion, the converging flow field drives extensive molecular chain alignment, promoting the γ-β phase transformation and substantially enhancing both β phase content and orientation. The synergistic effects of CTAB-induced ion-dipole interactions and the converging flow field further regulate the melting behavior and crystal perfection of PVDF, driving the transformation of the lamellar structure into highly oriented lamellar bundles along the extrusion direction. Among all compositions studied, the blends containing 5 wt% CTAB exhibit the optimal polar phase content and orientation characteristics, along with the highest dielectric constant. This work elucidates the synergistic regulation of PVDF hierarchical structures by ion-dipole interactions and flow fields, offering an effective strategy for fabricating high-performance piezoelectric PVDF materials.