Percolation threshold of aligned SWNT polymer composites prepared by mechanical stretching

摘要

The single-walled carbon nanotubes (SWNTs) filled nanocomposites SWNT/epoxy resin and SWNT/polyimide (PI) with good uniformity, dispersion and alignment of SWNTs and with different SWNTs concentrations were produced by solution casting and melt-mixing techniques, respectively. Subsequently, all the semidried mixture was stretched along one direction at a large draw-ratio of 50 and then folded it along the same direction and stretched repeatedly for 100 times at ambient atmosphere manually to achieve a good alignment and to prompt the dispersion of SWNTs in the composite matrix. The DC electrical volume conductivities of the composites rise with the increase of SWNT concentration, composites showed higher electrical conductivities along the stretched direction than perpendicular to it. With respect to pristine E-51, the electrical conductivity of 3 wt. % SWNT composite increases by 10 orders of magnitude, up to 10-6 S/cm. For SWNT/E51 composite with the same SWNTs loading of 1 wt. %, the conductivity along the stretching direction was 3 orders of magnitude higher than perpendicular to it. The percolation threshold value for both SWNT/epoxy resin and SWNT/ PI composites along the stretching direction is lower than the value perpendicular to the SWNTs orientation. For SWNT/epoxy composite, the percolation threshold value along the stretching direction is 0.05 wt.%, which is lower than the value of 1 wt.% perpendicular to the SWNTs orientation. The well aligned and dispersed SWNT modified SWNT/polymer composites follow percolation theory in a large SWNT loading rang from a small percolation threshold value to 10 wt. %.