Achieving large dielectric property improvement in polymer/carbon nanotube composites by engineering the nanotube surface via atom transfer radical polymerization

High dielectric constant (high-k) polymer composites have many applications in electrical insulation and energy storage systems because of their ease of processing. An important route to high-k polymer composites is to introduce high-aspect-ratio conductive nanoparticles (e.g., carbon nanotubes, CNTs) into a dielectric polymer. However, it is difficult to tune the dielectric properties of the composites via only adjusting the nanoparticle loading, particularly when the conductive nanoparticle concentration is near the percolation threshold. In this work, by using surface-initiated atom transfer radical polymerization, poly(methyl methacrylate) encapsulated CNTs (PMMA@CNTs) were prepared and used to tune the dielectric properties of PMMA composites. It was found that the PMMA@CNTs can be well dispersed into the PMMA matrix, regardless of the thickness of the PMMA shell grafted onto the CNT surface. The electrical parameters of the composites, such as percolation threshold, electrical conductivity, dielectric constant and dielectric loss tangent, can be tuned by controlling the thickness of the PMMA shell on the CNT surface. High dielectric constant and low dielectric loss can be achieved by adjusting the loading of PMMA@CNTs and the thickness of the PMMA shell on the CNT surface.