Control of carbon nanotubes at the interface of a co-continuous immiscible polymer blend to fabricate conductive composites with ultralow percolation thresholds

The concept of “double percolation”, i.e., conductive fillers are selectively located in one phase of a co-continuous polymer blend to form a percolated network in the selected phase, is widely used to reduce the percolation thresholds of conductive polymer composites to a fraction of their original values. However, it is expected that the percolation threshold can be significantly reduced further if the conductive fillers are only selectively distributed at the continuous interface of the co-continuous polymer blend, where only a very small amount of fillers are needed to build up the conductive percolated network. Multiwalled carbon nanotubes (MWCNTs) with very high aspect ratio (ca. 1000) are selectively distributed at a continuous interface of a co-continuous immiscible poly(lactic acid)/poly(ε-caprolactone) (PLA/PCL) blend at a weight ratio of 50/50 by controlling the migration process of MWCNTs from the unfavorable PLA to the favorable PCL phase. Compared to the PLA/PCL/MWCNTs composites by the traditional double percolation method (percolation threshold is ca. 0.97 wt%), the percolation threshold of PLA/MWCNTs/PCL composites (ca. 0.025 wt%) drops 2 orders of magnitude due to controlling the MWCNTs at the continuous interface between the PLA and PCL phases.