Covalent Introduction of Plasma-Treated carbon nanotubes into polyimide nanocomposites at Ultra-Low content

In this paper, the effect of plasma treatment on the structure of carbon nanotubes (CNTs) and the structure/properties of polyimide (PI) nanocomposites with CNTs at ultra-low content (0.001 wt% ∼ 0.004 wt%) were investigated. Plasma treatment of CNTs under the mixture-gas of N2 and CO2 resulted in introducing isocyanate group on the surface of CNTs. PI nanocomposites with non-treated CNTs (nCNTs) or plasma-treated CNTs (pCNTs) were synthesized by in-situ polymerization, where PI as well as polyamic acid (precursor of PI) was polymerized under the presence of fillers. The structural studies revealed that pCNTs were highly dispersed in the nanocomposites with the strong interfacial interaction of covalent bond at the interface between PI and pCNTs. As a result, the excellent reinforcement effect of CNTs was successfully exploited to the PI nanocomposites at ultra-low content. For example, the Young's modulus, tensile strength and toughness increased by 83 %, 51 % and 41 % by the incorporation of only 0.001 wt% of pCNTs, while the nanocomposite with nCNTs showed brittle behavior caused by poor interfacial interaction. Here in, we show that the characteristics of polymer matrices can be drastically changed by the addition of ultra-low content of nanofillers where the surface chemistry is optimized.