Understanding nucleation of the electroactive β-phase of poly(vinylidene fluoride) by nanostructures

Abstract

β-Poly(vinylidene fluoride) (PVDF) is of large technological relevance due to its piezoelectric, pyroelectric and/ferroelectric properties. In this way, a variety of methods have been developed to obtain such electroactive β-phase, being the addition of fillers one of the most popular, upscalable and innovative methods. The electrostatic interaction between negative charged fillers with the CH₂ groups having a positive charge density has been the most widely accepted mechanism for the direct formation of polar β-phase on nanocomposites. Nevertheless some controversy remains in this matter as the dominating crystallization into the β-phase within PVDF is sometimes attributed to the interaction between the positively charged surfaces of the fillers and the CF₂ dipoles in PVDF. In order to clarify such a controversial issue, this work uses two types of nanostructures, Fe₃O₄ nanorods and Fe₃O₄ nanoparticles, with distinct sizes and surface charges to study, isolate and evaluate the effects of the different ion–dipole interactions and shapes on the crystalline structures of PVDF. As a result it is shown that in the case of positive ion–CF₂ dipole based β-phase nucleation, and beyond the effect of the intermolecular interactions, the rod-shape optimizes the crystallization in the electroactive conformation, thus promoting current development in PVDF-based electroactive devices.