Solvent-Memory-Enabled Hierarchical Crystallization for Nested Spherulitic Architectures in Poly(vinylidene fluoride)

This study elucidates a nonclassical hierarchical crystallization pathway for constructing nested spherulitic architectures in poly(vinylidene fluoride) (PVDF) processed under high temperatures. Systematic investigations reveal that melting temperatures exceeding 250 °C induce the formation of γ-core/α-shell nested spherulites, whose population density increases with both melting and crystallization temperatures. Crucially, solvent polarity governs structural initiation: polar solvents (DMF, DMSO, and DMAc) imprint metastable trans-rich conformations during solution casting, which survive partial melting to template γ-phase nucleation─a phenomenon absent in weakly polar or nonpolar systems (CYC, THF). Dual prerequisites for nested spherulite formation are established: (i) high-temperature melting (>250 °C) to degrade heterogeneous nucleation sites and suppress α-phase dominance and (ii) polar solvent pretreatment to stabilize γ-favoring molecular conformations. In situ crystallization analysis demonstrates that α-phase overgrowth at γ-spherulite interfaces drives structural encapsulation, while residual α-nucleation limits architectural purity. These findings advance semicrystalline polymer design by introducing a solvent-memory-enabled crystallization paradigm, offering foundational insights for engineering PVDF polymorphic hierarchies in ferroelectric applications, where the γ-core/α-shell architecture may enhance interfacial polarization and phase transition efficiency.