Raman and Infrared Study of Polar Crystals in Poly(vinylidene fluoride) Electrospun Fibers and Films

Poly (vinylidene fluoride), PVDF, is a semi-crystalline polymorphic polymer with three stable crystalline forms. Its α crystalline phase is the most thermodynamically stable crystalline form with TGTḠ chain conformation. The polar β-crystallographic phase of PVDF with TTTT chain conformation is often used in fabricating piezoelectric and pyroelectric materials. α-phase PVDF films were prepared by compression molding PVDF powder at 200ºC and γ-phase films were prepared from solutions using dimethylacetamide. Fibers were formed by electrospinning, which is known to produce dominantly β-phase crystals. The crystalline fractions in different PVDF samples were controlled by applying various heat treatments to the films and changing electrospinning parameters in fiber preparation. Raman and Fourier-transform infrared spectra of PVDF samples were analyzed to determine specific precursors for each crystalline phase. Variations in the α-, β-, and γ-phase crystalline fractions were then determined from this analysis.