Introductory Remarks

Since their discovery in 1991, carbon nanotubes (CNTs) have been of great interest to the scientific community due to their outstanding electrical, thermal, and mechanical properties. Unfortunately, it has been challenging to translate the excellent properties of single CNT molecules into macroscale materials. A promising technique for obtaining high performance fiber materials is wet-spinning solutions of CNTs in chlorosulfonic acid (CSA). CSA and other superacids overcome the strong van der Waals forces between the CNTs by protonating the sidewalls of the CNTs to individualize the molecules to form a true solution. The CNTs in solution follow classical soft matter physics behavior; the solutions are isotropic at low concentration and liquid crystalline at sufficiently high concentration. The transition between these phases depends on the aspect ratio (the ratio of the length of the CNT to the diameter). Here, we study how the rheology and phase behavior of the solutions affect the spinning process and the electrical and mechanical properties of the resulting fibers. We have examined this experimentally by varying key processing parameters such as solution extrusion rate, CNT solution concentration, fiber draw ratio, and choice of coagulant. We find that spinning at lower concentrations yields significant improvement in tensile strength but no change in conductivity. Preliminary tensile testing data demonstrates that fibers spun from lower concentration solutions have a higher elongation a break. This suggests that the improvement in tensile strength can be attributed to the formation of larger bundles of CNTs within the fiber. This study along with continued research on the fluid behavior of CNTs will enable us to create the next generation of wires and cables.