Electrophoretic drawing of continuous fibers of single-walled carbon nanotubes

Control over the current during electrophoretic drawing of continuous fibers of single-walled carbon nanotubes (SWCNTs) is shown to be critical in producing long fibers with specific diameters. In the process, as-produced SWCNTs are first dispersed in N,N-dimethylformamide (DMF) by sonication. A tungsten probe tip is then immersed in the SWCNT/DMF solution, and a dc bias is applied between the tip and another electrode at the bottom of the beaker containing the solution. After a dark cloud several millimeters in diameter develops around the tip, the electrode is withdrawn to form continuous macroscopic fibers of SWCNTs. The resulting fiber length and diameter are found to be principally determined by the magnitude of the current. Under constant voltage conditions where the current is allowed to vary, the fibers are short (several millimeters long) and their diameters vary drastically along their lengths. Of significance is the fact that when the current is maintained at constant values, fibers several centimeters in length with uniform diameters ranging from 26 to 42 mu m are obtained at a withdrawal rate of 0.85 mu m/s. For this withdrawal rate, long fibers (similar to 3 cm and greater) are obtained at an optimum value of the current (400 nA) using hybrid conditions where the voltage is maintained constant earlier in the process while the current is maintained constant later in the process. Control of the total current at low values during this process has the potential to produce long fibers with uniform submicron diameters.