Exfoliation in ecstasy: liquid crystal formation and concentration-dependent debundling observed for single-wall nanotubes dispersed in the liquid drug gamma-butyrolactone

摘要

Large-scale debundling of single-walled nanotubes has been demonstrated by dilution of nanotube dispersions in the solvent. gamma-butyrolactone. This liquid, sometimes referred to as 'liquid ecstasy', is well known for its narcotic properties. At high concentrations the dispersions form an anisotropic, liquid crystalline phase which can be removed by mild centrifugation. At lower concentrations an isotropic phase is observed with a biphasic region at intermediate concentrations. By measuring the absorbance before and after centrifugation, as a function of concentration, the relative anisotropic and isotropic nanotube concentrations can be monitored. The upper limit of the pure isotropic phase was C-NT similar to 0.004 mg ml(-1), suggesting that this can be considered the nanotube dispersion limit in. gamma-butyrolactone. After centrifugation, the dispersions are stable against sedimentation and further aggregation for a period of 8 weeks at least. Atomic-force-microscopy studies on films deposited from the isotropic phase reveal that the bundle diameter distribution decreases dramatically as concentration is decreased. Detailed data analysis suggests the presence of an equilibrium bundle number density. A population of individual nanotubes is always observed which increases with decreasing concentration until almost 40% of all dispersed objects are individual nanotubes at a concentration of 6 x 10(-4) mg ml(-1). The number density of individual nanotubes peaks at a concentration of similar to 6 x 10(-3) mg ml(-1) where almost 10% of the nanotubes by mass are individualized.