Effect of Ionic Liquid Content on the Crystallization Kinetics and Morphology of Semicrystalline Poly(vinylidene Fluoride)/Ionic Liquid Blends

The crystallization kinetics of poly(vinylidene fluoride) (PVDF) in blends with the ionic liquid (IL) 1-ethyl-3-methylimidazolium chloride [Emim][Cl] has been studied as a function of [Emim][Cl] content up to 40 wt %. Blends were produced by a solvent casting technique from diluted solutions and solvent evaporation at a temperature higher than the melting point of PVDF followed by cooling to room temperature. Polymer phase, morphology, and crystallization behavior were evaluated. When the molten blend was crystallized from the melt, it was observed that [Emim][Cl] induces nucleation of PVDF in the electroactive and highly polar beta-crystalline phase, while pure PVDF crystallizes in the a phase with the same thermal treatments. It is shown that PVDF crystal growth segregates an amorphous phase rich in IL molecules to the surface of the films and that the IL also remains in the spaces between the lamellae or between spherulites as demonstrated by scanning electronic microscopy (SEM) and polarizing optical microscope (POM) images. Differential scanning calorimetry results of isothermal crystallization show the dependence of equilibrium melting temperature and the Avrami exponent with the [Emim][Cl] content.