Manipulation of the microenvironment surrounding single wall carbon nanotubes and its effect on photoluminescence and separation processes

The photoluminescence from single wall carbon nanotubes (SWNTs) has been studied after manipulating the immediate environment surrounding SWNTs. First, the effect of shearing on the assembly of sodium dodecyl sulfate (SDS) on the surface of SWNTs is probed. Shearing SWNTs coated with sodium SDS in microfluidic channels significantly increases the photoluminescence (PL) intensity and dispersion stability. These improvements are attributed to surfactant reorganization rather than disaggregation of SWNTs bundles or shear-induced alignment. The results highlight potential opportunities to eliminate discrepancies in the PL intensity of different suspensions and further improve the PL of SWNTs by tailoring the surfactant structure around SWNTs. Second, SWNTs are encapsulated with microenvironments of nonpolar solvents, providing a new method to measure the photophysical properties of nanotubes in environments with known properties. Photoluminescence (PL) and absorbance spectra of SWNTs show solvatochromic shifts in 16 nonpolar solvents, which are proportional to the solvent induction polarization. The solvatochromic shifts of SWNTs were used to determine the relationship between the longitudinal polarizability, band gap and radius, alpha 11,|| ∝ 1/(R² E311 ).;Elution chromatography through columns packed with agarose beads has been used to separate metallic from semiconducting SWNTs. Prior studies have attributed the separation to either selective adsorption or size-exclusion (due to selective aggregation) of semiconducting SWNTs. Initial SWNT suspensions with different aggregation states were prepared to test these competing theories. The selective adsorption of nanotubes on the agarose matrix is confirmed by modifying the surfactant structure around the SWNTs without changing the aggregation state of the suspension. In addition, salt-modifiers and solvent-modifiers allow systematic changes to the surfactant aggregation number, orientation, and sidewall coverage. The retention characteristics from these modified SWNT suspensions suggest that surfactant orientation rather the exposed regions on the surface of the nanotubes is the dominant factor in the adsorption process.;Small-angle neutron scattering (SANS) is used to study the formation of nonpolar solvent microenvironments on the SWNT surface. It was determined that the solubilization of the nonpolar solvents by the SDS molecules assembled on the SWNT surface do not change the aggregation state of the dispersed nanotubes. In addition, it was possible to obtain the characteristic lengths that describe the solvent microenvironments around SWNTs.