TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The carbon nanotube composition is introduced into the first fluid medium at a density less than 1.095 g/ml; further involves centrifuging an enriched separation fraction in contact with a second fluid medium comprising a second density gradient, where the enriched separation fraction comprises carbon nanotube subpopulation comprising a higher percentage of double-walled carbon nanotubes than the carbon nanotube population, where the enriched separation fraction is introduced into the second fluid medium at a density greater than 1.115 g/ml, and the carbon nanotube population comprises multi-walled carbon nanotubes comprising at least three walls. Preferred Components: The at least two separation fractions are visibly distinguishable by the human eye, where the carbon nanotube population comprises double-walled carbon nanotubes having a mean outer wall diameter of less than 1.7 nm and single-walled carbon nanotubes having overlapping outer wall diameters, and at least one of the at least two separation fractions comprises a carbon nanotube subpopulation contain a higher percentage of single-walled carbon nanotubes than the carbon nanotube population. The carbon nanotube population comprises double-walled carbon nanotubes having a semiconducting outer wall single-double-walled carbon nanotubes (s-DWCNTs), and double-walled carbon nanotubes having a metallic outer wall (m-DWCNTs), and the at least two separation fractions comprise a first separation fraction contain a carbon nanotube subpopulation comprising a higher percentage of s-DWCNTs than the carbon nanotube population, and second separation fraction comprising a carbon nanotube subpopulation comprising higher percentage of m-DWCNTs than the carbon nanotube population. The carbon nanotube composition comprises at least one surface active components and a DWCNT population having more than one outer wall diameter or chirality, the at least two separation fractions comprise at least one separation fraction comprising a DWCNT subpopulation comprising a higher percentage of DWCNTS having an outer wall diameter within a selected outer wall diameter or chirality range than the DWCNT population. The at least two surface active components comprise a planar surface active component and a linear surface active component, where the carbon nanotube population comprises semiconducting single-walled carbon nanotubes (s-SWCNTs) and metallic single-walled carbon nanotubes (m-SWCNTs), and where after the centrifuging step, the carbon nanotube composition is separated simultaneously by wall number and by outer wall electronic type into at least four separation fractions, the at least four separation fractions comprising the first separation fraction, the second separation fraction, third separation fraction comprising a carbon nanotube subpopulation comprising a higher percentage of s-SWCNTs than the carbon nanotube population, and a fourth separation fraction comprising a carbon nanotube subpopulation comprising a higher percentage of m-S WCNTs than the carbon nanotube population, where the relative ratio of the at least two surface active components is selected to cause metallic carbon nanotubes to have a lower buoyant density than semiconducting carbon nanotubes regardless of wall number, or semiconducting carbon nanotubes to have a lower buoyant density than metallic carbon nanotubes of the same wall number, or metallic carbon nanotubes to have a lower buoyant density than semiconducting carbon nanotubes of the same wall number. In population (P1), where greater than 70, 75, 80, 85, 90, 95, 97, or 99% of the double-walled carbon nanotubes comprise a metallic outer wall. The population of double-walled carbon nanotubes has a mean outer wall diameter of less than 1.7 nm. In population (P2), where greater than 50, 75, 90, % of the double-walled carbon nanotubes comprise an outer wall having the same chirality (n,m) type. EXAMPLE - No suitable example given.