Negative permittivity in polymer nanocomposites: Influences of size distribution of carbon nanofiber networks

In our previous study, a polymeric "single negative permittivity metamaterial" was successfully fabricated from organic polyetherimide (PEI) and non-metallic carbon nanofibers. The determinant structure in polymer nanocomposites is the continuous 3D network composed of imide chains wrapped on long CNFs (CNF agglomerates), which is equivalent to the thin metallic wires in J.B.Pendry's Model. In this study, the low power ultrasonic treatment was applied to disentangle the big CNFs agglomerates into smaller ones, and consequently change the size of CNF agglomerates and their distribution. The results showed that the size of CNFs agglomerates exerts great influence on the occurrence of negative permittivity. A qualitative relationship between size/size distribution and negative permittivity of PEI/CNF nanocompositcs was established.