A two-step shearing strategy to disperse long carbon nanotubes from vertically aligned multiwalled carbon nanotube arrays for transparent conductive films

A surfactant-free two-step shearing strategy was applied to disperse vertically aligned carbon nanotube (VACNT) arrays into individually dispersed CNTs. First, big blocks of VACNT arrays were sheared into fluffy CNTs. The fluffy CNTs were composed of CNT bundles with a diameter of 1-10 μm and a length of several millimeters. After that, the fluffy CNTs were further sheared in liquid phase to obtain individually dispersed CNTs. As comparison, sonication and grinding were also employed for further dispersion of the fluffy CNTs. The length of CNTs dispersed by shearing method was the longest and up to several hundred micrometers. The CNT dispersions from the three methods can be used to fabricate transparent conductive films (TCFs). The TCFs from CNTs dispersed by shearing method showed the highest conductivity at the same transparency. VACNT arrays with a small diameter (∼10 nm) were dispersed by the shearing method as well, from which the TCF with a surface resistance of 2.5 kΩ/□ and a transparency of 78.6% (at 500 nm) was obtained. The ratio of dc to optical conductivity (σ_dc/σ_op) of the as-dispersed CNT array was 0.711, which can compare beauty with that of single-walled CNTs and double-walled CNTs grown by the CVD process.