Fabrication of a highly tough, strong, and stiff carbon nanotube/epoxy conductive composite with an ultralow percolation threshold via self-assembly

Conductive epoxy composites are of great interest in industrial applications. The electrical properties of these composites, however, often come at the expense of mechanical properties, particularly toughness. Herein, we report a simple, facile, and universal fabrication method for a strong, stiff, and extremely tough conductive epoxy composite with an ultralow percolation threshold. By tuning the interaction between multi-walled carbon nanotubes (MWCNTs) and epoxy components, they spontaneously assembled into a "cellular structure", with the MWCNTs selectively located in the continuous domain of the diglycidyl ether of bisphenol A (DGEBA) epoxy. These cellular structures dramatically improved the toughness of the epoxy resin and the electrical properties of the MWCNT/epoxy composites while maintaining an excellent tensile strength and modulus. A 26.83-fold increase in toughness (to 3.25 +/- 0.12 GJ m(-3)) was seen in the MWCNT/DGEBA/tung oil-based diglycidyl ester (TODGE) epoxy composite (0.75 wt% MWCNTs). The elongation at break of the composite increased 33.93 times (to 112.84 +/- 4.25%) over that of neat DGEBA epoxy (toughness: 116.76 +/- 7.84 MJ m(-3); elongation at break: 3.23 +/- 0.25%). The tensile strength and modulus remained at 37.09 +/- 1.28 MPa and 2.88 +/- 0.14 GPa, respectively. Moreover, composites with the cellular structure exhibited an ultralow electrical percolation threshold (similar to 0.032 wt%). The outstanding toughness and good electrical properties of the MWCNT/epoxy composites with cellular structures are attributed to the synergistic toughening effects of TODGE and MWCNTs as well as volume exclusion from the cellular structure. This work provides a new strategy for designing mechanically robust multifunctional thermoset composites, which have important applications in various fields.