Dispersion of carbon nanotubes by carbazole-tailed amphiphilic imidazolium ionic liquids in aqueous solutions

Surfactants with a polycyclic aromatic moiety and a long hydrocarbon chain, carbazole-tailed amphiphilic imidazolium ionic liquids 1-[n-(N-carbazole)alkyl]-3-methylimidazolium bromide [CzC(n)MIm]Br (n=10 and 12), were designed to disperse carbon nanotubes (CNTs) in aqueous solutions. UV-vis-NIR spectra were performed to determine the dispersion of CNTs and the optimal concentration (C(opt)) of [CzC(n)MIm]Br. Compared with [C(n)MIm]Br, [CzC(n)MIm]Br was more effective with the smaller C(opt) and more individual CNTs, reflecting the effect of the carbazole moiety. The adsorption of [CzC(n)MIm]Br molecules on CNTs was investigated by zeta-potential, surface tension, fluorescence, and (1)H NMR. Having zeta-potentials higher than 15mV contributed to the long-term stability of aqueous CNT dispersions. The significant fluorescence quenching and the upfield shift of carbazole protons support the π-π stacking interaction between carbazole moieties and the π-networks of CNTs. Meanwhile, the upfield shift of imidazolium protons indicates the cation-π interaction between the imidazolium ions and the π-networks of CNTs.