Microstructure development in electrospun carbon nanotube reinforced polyvinylidene fluoride fibers and its influence on tensile strength and dielectric permittivity

Electrospinning was used to process polyvinylidene fluoride (PVDF)/carbon nanotube (CNT) fibers. Aided by high electrostatic and extensional forces, the CNTs were uniformly dispersed within the fibrous matrix and aligned along the fiber axis. The dispersed CNTs served as nucleating agents and provided confinement to the segmental motion of neighboring chains. The structural developments induced by the presence of the CNTs not only improved the content of ferroelectric β-phase within the fibers but also improved the dielectric properties of the fibers and served to strengthen and stiffen the fibers. The conformal changes were determined using X-ray diffraction (XRD) and infrared (IR) spectroscopy methods. The content of β-crystals within the fibers increased consistently with CNT concentration. Compared to the neat fibers, the content of β-crystals for fibers filled with 3wt% CNT was increased by 5.5%. This was attributed to the CNTs, which converted the molecules of the α-phase to an extended chain conformation. The improvement in the polar crystalline (β) content within the fibers increased the dielectric permittivity of the fibers. Additionally, the dielectric loss of the CNT reinforced fibers was as low as the neat PVDF fibers, which is significant for dielectric applications. The oriented β-crystalline structure also improved the tensile properties of the fibers. Strength and stiffness of the fibers were improved by 28% and 32%, respectively, when 3wt% CNT was incorporated within the fibers. Understanding the effect of CNTs on crystal polymorphism and tensile strength of PVDF fibers has provided new insights for future development of high-performance ferroelectric fibers.