Endohedral Filling Effects in Sorted and Polymer-Wrapped Single-Wall Carbon Nanotubes

Widespread use of the polymer extraction method for single-wall carbon nanotubes (SWCNTs) and the ability of endohedral functionalization to alter their material properties make it important to examine the effect of filling on the separation result. Rate-zonal centrifugation is used to obtain empty, water-filled and perfluorooctane-filled large (∼1.45 nm), and single-chirality small (∼0.78 nm) diameter SWCNTs. These are transferred from water to toluene by dispersion with poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(6,6′-(2,2′-bipyridine))] (PFO-BPy), and absorption and Raman spectroscopy are used to follow the extent of endohedral filling at each step. Measurements are made before and after centrifugation (supernatant) but also in the pellet. PFO-BPy is found to stabilize endohedral-functionalized SWCNTs in the supernatant, but a clear preference for less-filled or empty species is shown. Molecular dynamics simulations are used to model the absorption spectrum of encapsulated water molecules in the PFO-BPy/SWCNT/toluene system and explain why partial water filling is difficult to directly measure. These findings are then used to interpret separation results obtained for raw soot (without intentional filling) and with a view to the low yield of polymer-based SWCNT extraction.