Comparison of the stability of multiwalled carbon nanotube dispersions in water

Continuous real-time monitoring of the nanotube concentration in aqueous solution using UV-Vis spectroscopy allows quantitative comparison of the stability of different types of nanotube dispersions. Systematic investigation of the e. ects of nanotube length and functionalisation for thin multiwalled carbon nanotubes ( MWNT) has revealed that shorter MWNT form more stable dispersions than longer nanotubes of the same diameter. MWNT shortened to an average length of approximately 1 mm form stable dispersions in water with concentrations up to 0.013 mg ml(-1) in the absence of surfactants or solubilising functional groups. The introduction of carboxylic or thiol groups on the surface of shortened nanotubes further increases the stability of MWNT dispersions ( up to 0.24 mg ml(-1)). The introduction of surfactant or surface charge on MWNT has contrasting effects on functionalised and non-functionalised nanotubes, destabilising and stabilising their dispersions, respectively.