The single-walled carbon nanotubes (SWNT)-N-methyl-pyrrolidone (NMP) interactions were demonstrated to lead to zero enthalpy of mixing and a negative free energy of mixing. AFM analysis show that if nanotubes form a colloidal dispersion, the mean bundle diameter is constant for all concentrations in the absence of sonication. The fraction of individual nanotubes increases with dilution, saturating at ca. 20% at low concentration, and the PL intensity is expected to display similar concentration. The dispersibility of CNTs plotted as a function of solvent surface tension shows that a strong peak is observed at 40 mJm-2. N,N-dimethyl formamide (DFM) and dimethylacetamide (DMA) are found to have excellent nanotube dispersal properties. The NMP is expected to chemisorb on the Si(100) surface through the nitrogen-containing group.