Carbon Nanotubides: an Alternative for Dispersion, Functionalization and Composites Fabrication
Marti, Angel A.; Pasquali, Matteo; Wilson, Lon J.
Doctor of Philosophy
Negatively charged single-walled carbon nanotube (SWCNT), also called SWCNT polyelectrolytes and single-walled carbon nanotubides (SWCNTDs), are formed by the reduction (either chemical or electrochemical) of the SWCNT wall by alkali metals (or an electrode) to form negative charged SWCNTs surrounded by an alkali metal counter ions. SWCNT polyelectrolytes can spontaneously dissolve in a variety of polar aprotic solvents without assistance of sonication and will readily react with alkyls and aryls halides to functionalize the walls of SWCNTs. Although SWCNT polyelectrolytes present a good alternative for achieving high concentration of SWCNTs in solution, the condensation of the counter ions on the surface of negatively charged SWCNTs partially shield their charge, limiting the solubility of SWCNT polyelectrolytes. For HiPco SWCNT polyelectrolytes, the highest solubility reported before this work was only 0.4 mg/mL in DMSO. However, we developed a method that greatly improve the solubility of SWCNTs by adding crown ether into the system to coordinate the potassium cation and thus separate the negatively charged SWCNTs from counter ions. This new method produces a high concentration of SWCNT polyelectrolytes up to 9.2 mg/mL in DMSO. In addition, we were able to observe the formation of liquid crystalline phases at highly concentrated solutions, which has been proved to be an essential factor for manufacturing highly ordered robust macroscopic materials. After applying a more efficient dispersion method, speed-mixing, the concentration of SWCNT polyelectrolytes can be further improved up to 52 mg/mL. Compared with previous reported results, the increase in solubility is more than 100 times. As mentioned above, we achieved high concentration of SWCNT polyelectrolytes by adding crown ether to the mixture and using speed-mixing. The SWCNTs in these solutions spontaneously align forming liquid crystalline solutions that can be manufactured into strong and conductive carbon nanotubes fibers by spinning the SWCNT dispersions into aqueous coagulation solutions. The best fibers we have obtained by this method have tensile strength up to 124 MPa, which compares to HiPco SWCNT fibers spun from superacid solutions, and conductivity 2 × 104 S/m. Our method provides an acid-free alternative towards high performance carbon nanotube fibers, which can be expanded for the production of other materials such as films. Also, we expanded our methodology to disperse graphite intercalation compounds (GICs) into graphene polyelectrolytes. Graphene polyelectrolytes, when mixed with SWCNT polyelectrolytes were spun onto SWCNT/Graphene hybrid fibers, which maintains a similar tensile strength (as for HiPco SWCNT fibers) while the Young’s modulus increases by 70% and conductivity increases 2 times.
Carbon Nanotubide; Carbon Nanotube Fiber; Graphenide