High-permittivity and low-dielectric-loss polymer composites based on TiO2-nanorod functionalized carbon nanotubes

High permittivity polymer-based composites have attracted increasing attention because of their inherent advantages of being easy to process, flexible and light weight in electronic and electrical industry. However, the permittivity of common polymer is very low (<;10). Adding conductive fillers provides a promising route to significantly increase the permittivity of a polymer with a low loading. Nevertheless, polymer composites containing conductive fillers often exhibit very high dielectric loss due to their large electrical conduction or leakage currents. In this paper, we report a simple and effective way to synthesize TiO₂-nanorod-decorated multi-walled carbon nanotubes (TD-CNTs). The resultant TD-CNT/polystyrene (PS) composites show high permittivity and low dielectric loss. The composites with 17.2 vol% TD-CNTs show a permittivity of 37 at 1 kHz, which is 13.7 fold higher than that of the pure PS, but the dielectric loss still shows a low level below 0.11.

I. Introduction

Polymer composites with high permittivity have attracted increasing interest for applications in integrated capacitors, actuators, piezoelectric and pyroelectric sensors, and electric capacitors because of their flexibility, easy processing and low cost.¹ However, the permittivity of common polymers is very low . A common route to improve the permittivity of host polymer is to add high-permittivity ceramic materials.² High loading levels of ceramic powders are often required for achieve high enough permittivity, thus, the obtained composites show deteriorated physical and processing performance. Another route is to fabricate insulator/conductor percolative composites, which can exhibit high permittivity while the volume fraction of the fillers approach to the vicinity of the percolation threshold.³ Currently, percolative composites have been wildly investigated using different conductive fillers, such as metal fillers, carbon black, carbon nanotubes (CNTs), and graphene sheets. However, these types of percolative composites exhibit not only large permittivity but also high dielectric loss because of their high leakage current. It is well known that high leakage current mainly origins from direct contact of partial conductive fillers in the composites near percolation threshold. Thus, a key issue for obtaining high permittivity and low loss is to prevent contact between the conductive fillers in polymer matrix by effectively confining fillers within individual interfacial layers.