Stable dispersions of double-walled carbon nanotubes for carbon nanotube/copper co-deposition

This work explores a novel approach to disperse purified double-walled carbon nanotubes in high ionic strength aqueous media, i.e. a copper ion solution to further prepare double-walled carbon nanotubes/Cu composites by co-electrodeposition. Firstly, the metal catalyst impurities in the tube samples are selectively removed by a one-pot gas-phase purification treatment. Two non-ionic (Triton X-100 and Pluronic-P123) and one anionic (sodium dodecyl sulfate) surfactant were used to disperse the purified samples by varying the carbon nanotubes/surfactant ratio and the surfactant content. Triton X-100 is a poly(ethylene glycol) in which one of the terminal hydroxy groups has been converted into the corresponding p-(2,4,4-trimethylpentan-3-yl)phenyl ether. Pluronic-P123 is a triblock copolymer comprising poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) leading to PEO-PPO-PEO. Sodium dodecyl sulfate of chemical formula C12H25OSO2ONa possesses a sulfate head and a hydrocarbon tail. The capability of each surfactant to disperse the double-walled carbon nanotubes in the copper ion solution is analyzed and later discussed based on the nature of the inter-tube forces. Among the employed surfactants, Pluronic-P123 exhibits the best dispersive level since stable and homogenous suspensions of double-walled carbon nanotubes are obtained. The dispersion mechanism proposes that the hydrophobic nature of Pluronic-P123 promotes efficient steric repulsions allowing the stable dispersion in the copper electrolyte. The samples dispersed by this way are successfully co-deposited and they form well-distributed double-walled carbon nanotubes within the copper matrix. The obtained results are an important step on the way to achieving an efficient double-walled carbon nanotubes/Cu composite synthesized by electrodeposition means.