Fabrication of Ferroelectric Polymer Nanocrystals with Tunable Morphologies

Abstract

We developed a procedure for the reliable and reproducible formation of monodispersed polymer nanocrystals whose morphologies can be easily controlled to produce structures ranging from nanoparticles to nanorods. The directional cooling crystallization of ferroelectric polymer solutions under nanoconfinement allowed polyvinylidene fluoride to form single crystalline monodisperse nanocrystals without the use of surfactants or stabilizers. An important growth condition necessary to yield highly crystalline ferroelectric polymers was a regulated thermal gradient under nanoconfinement to induce uniform nucleation and controlled directional growth. While other methods involving the nanoconfined crystallization of polymers are restricted to yield nanofibers or nanotubes with a high aspect ratio, our unidirectional cooling method produced nanocrystals of ferroelectric polymers with nanosphere, nanocapsule, and nanorod structures. Field-emission scanning electron microscopy, transmission electron microscopy, dynamic contact electrostatic force microscopy, grazing incidence X-ray diffraction, and differential scanning calorimetry were used to characterize the morphologies and structures of the nanocrystals. The results suggest that the directional cooling method facilitates nucleation and directional growth by controlling diffusion and promoting molecular alignment from the preferred crystal orientations due to the unidirectional thermal gradient. This study provides a novel method of rational material design to fabricate polymer nanocrystals by directing nucleation and growth of molecular crystals from solution.