Study On Dielectric Behavior Of Carbon Nanofiber/Poly(Vinylidene Fluoride)Composite Membranes

With the rapid development of electronic, electrical industry, the demand for dielectric materials with excellent overall performance has increased greatly. Conventional ferroelectric ceramic dielectric cannot meet the requirements of diversified shape and light weight for its bad processing performance and high density. As a new type of dielectric material, polymer matrix composites (PMC) material has drew a lot of attention for having excellent dielectric properties and easy processing and tunable properties. Carbon nanofibers (CNFs) has excellent electrical conductivity and a high aspect ratio, making the key reason of the rather low percolation threshold of the composite, which can have a very high dielectric permittivity when reaches the percolation threshold.In this work, CNFs and polyvinylidene fluoride (PVDF) are used as fillers and matrix respectively, and the influence of CNFs on the dielectric properties of CNFs/PVDF composites has been studied. Efforts have been made to work with the solution of CNFs/PVDF composites with excellent and stable dielectric properties.CNFs with variable aspect ratios (AR) have been prepared through ultrasonication, and the effects of CNFs AR on the CNFs/PVDF composite dielectric properties are studied, also with the dependence of dielectric properties on the frequency and filler content. CNFs with smaller AR have a better dispersion in the polymer matrix, and the percolation threshold of the composites decreases first and then increases as the AR decreases.Polyetherimide (PEI) and aluminum hydroxide oxide (AlO(OH)) has been used as coatings for the modification of CNFs, resulting with PEI-coated CNFs and AlO(OH)-coated CNFs. Experiment results show that the surface modification of CNFs can improve the dielectric properties of CNFs/PVDF composites, with increased dielectric permittivity, lower dielectric loss, and more stable dielectric properties. Compared with CNFs composites, ones with modified CNFs have a higher percolation threshold:PEI-coated CNFs/PVDF composites have a percolation threshold value of1.06wt%, and AlO(OH)-coated CNFs/PVDF composites4.51wt%.CNFs/PVDF nanofiber membranes can be made by electrospinning method, and further more CNFs/PVDF nanofiber laminates can be made by hot pressing stacked nanofiber membranes. Due to the special morphology and structures of the nanofiber membranes, CNFs/PVDF nanofiber composite materials exhibit unique dielectric properties. The dielectric permittivity of the nanofiber membrane composites is very low, about1to2, while for nanofiber laminates, the dielectric permittivity is23when the CNFs content reaches2wt%with a rather low dielectric loss and AC conductivity.