Assembly of Highly Aligned Carbon Nanotubes Using an Electro-Fluidic Assembly Process.

Carbon nanotubes (CNTs) are promising building blocks for emerging wearable electronics and sensors due to their outstanding electrical and mechanical properties. However, the practical applications of the CNTs face challenges of efficiently and precisely placing them at the desired location with controlled orientation and density. Here, we introduce an electro-fluidic assembly process to assemble highly aligned and densely packed CNTs selectively on a substrate with patterned wetted areas at a high rate. An electric field is applied during the electro-fluidic assembly process, which drives the CNTs close to the patterned regions and shortens the assembly time. Meanwhile, the electric field orientates the CNTs perpendicular to the substrate and anchors one end of the CNTs onto the substrate. When pulling the substrate out of the CNT suspension, the capillary force at the air-water-substrate interface stretches the free end of the CNTs and aligns the CNTs along the pulling direction. By adjusting two governing parameters, the direct current voltage and the pulling speed, we have demonstrated well aligned CNTs assembled in patterns with widths from 1 to 100 μm and lengths from 20 to 120 μm at a rate 20 times higher than a fluidic assembly process. The aligned CNTs show improved electrical conductivity compared with the random networks and prove possibility for strain detection. Precise and reproducible control of the orientation and the placement of the CNTs opens up their practical application in the next-generation electronics and sensors.