Dispersing carbon nanotubes in the unfavorable phase of an immiscible reverse-phase blend with Haake instrument to fabricate high-k nanocomposites with extremely low dielectric loss and percolation threshold

Abstract

How to facilely obtain low dielectric loss and extremely low percolation threshold (Pc) is still a key and interesting issue of developing high-k conductor/polymer composites based on common components. Different from available literatures, a new type of an immiscible polymer blend that has a reverse-phase morphology, consisting of poly(ether imide) (PEI)/bismaleimide (BD) (20PEI/BD), was selected as the matrix. Note that multi-walled carbon nanotubes (MWCNTs) prefer to disperse in BD but not PEI phase, so this is the common morphology in the MWCNT/20PEI/BD composites through traditional blending method, and the corresponding dielectric properties are not attractive. To overcome this challenge, a new kind of h-MWCNT/20PEI/BD composites of which MWCNTs were stably and uniformly dispersed in PEI continuous phase by Haake instrument with two steps were fabricated at first time. Compared with MWCNT/20PEI/BD composites, the h-MWCNT/20PEI/BD composite has remarkably higher dielectric constant and energy storage density as well as lower dielectric loss; besides, the Pc of the latter is as low as 0.35wt%, only 60% of that of the former. Specifically, the dielectric constant and loss at 100Hz of h-0.45MWCNT/20PEI/BD composite with 0.45wt% MWCNTs are about 25 and 0.8 times of those of 0.5MWCNT/20PEI/BD composite with 0.50wt% MWCNTs, respectively. The origin behind the attractive results was discussed through intensively investigating the structure of these composites and building equivalent circuits.