(450i) Analytical Ultracentrifugation Based Quantification of the Packing Density of Linear Alkanes Inside ~1.5 Nm Diameter Single-Wall Carbon Nanotubes

In this contribution I will present the precise determination via analytical ultracentrifugation (AUC) of the packing density of linear alkane molecules inside single-wall carbon nanotubes (SWCNTs) in a colloidal dispersion of ~1.45 nm diameter highly purified SWCNTs sorted for rod length and semiconducting nature of the SWCNT. Confinement inside SWCNTs, well-defined cylindrical structures of sp2-bonded carbon, has tremendous potential for studying the effects of packing at the nanoscale in a 1-D geometry, with pore size control from < 0.5 nm to ~3 nm. As such, a variety of physical experimental methods and computational experiments have reported on the quantity or structure of adsorbed molecules inside SWCNTs, but by methods probing heterogeneous nanotube powders or without valid experimental references. This work provides a reference point using highly purified SWCNTs for the comparison of density differences from hydrogenated and deuterated alkane-filling of the interior SWCNT cavity, along with additional comparison to empty and water-filled SWCNTs. The results suggests near bulk like densities for both alkane and water filler molecules despite the strong confinement, ≈ 1.1 nm diameter, of the SWCNT interior, and provide specific constraints to future analytical and computational models of SWCNT filling and the diameter of transition to pseudo-bulk behavior.