Wet spinning of multi-walled carbon nanotube fibers

For the commercialization of macroscopic fibers of carbon nanotubes (CNTs), it is important to achieve solution processing using inexpensive commercial multi-walled carbon nanotubes (MWCNTs). However, so far, the solution processing of CNTs has been limited to single-walled CNTs (SWCNTs). Here, we report wet spinning of MWCNT fibers using a high-concentration MWCNT/surfactant dispersion in water for the first time. We established the phase diagram of MWCNT/surfactant dispersion by varying the mass ratio of surfactants and MWCNTs. The phase diagram successfully accounts for the phase behavior based on the balance between depletion-induced attraction from surfactant micelles and electrostatic repulsion from adsorbed surfactants on MWCNTs. Following the phase diagram, we obtained a homogeneous MWCNT dispersion with high concentration (1.4 wt%), which enabled us to fabricate MWCNT fibers by wet spinning.