(73c) Improving the Effectiveness of Interfacial Trapping

Single-walled carbon nanotubes can be coated with surfactants or polymers to aid dispersion but bundled nanotubes remain due to large van der Waals attractions. Recently, we showed that liquid-liquid interfaces could be used to remove nanotube bundles from aqueous suspensions. A simple model has been developed to characterize the free energy changes upon movement of nanotubes from the aqueous phase to the interface. This model predicts that bundled nanotubes preferentially adsorb at the interface because of changes in free energy. Further improvements to the dispersion quality can be obtained by introducing different solvent ratios, a second extraction step, and other organic solvents. After the improvements, the interfacial trapping process has dispersion characteristics comparable to and, by some measures, better than ultracentrifugation. Interestingly, in some systems, mixing an organic solvent with the aqueous suspension results in solvatochromic shifts in the fluorescence and absorbance spectra. These shifts indicate a change in the nanotube environment which is attributed to swelling of the surfactant micelle. These shifts can be measured for a wide variety of solvents which may provide new information about the surfactant structure surrounding carbon nanotubes and their photophysical properties.