A Mechanistic Study of the Selective Retention of SDS-Suspended Single-Wall Carbon Nanotubes on Agarose Gels

Elution chromatography through columns packed with agarose beads has been used to separate metallic from semiconducting single-wall carbon nanotubes (SWCNTs). Prior studies have attributed the separation to either selective adsorption or size-exclusion (due to selective aggregation) of semiconducting SWCNTs. Initial SWCNT suspensions with different aggregation states were prepared to test these competing theories. Retention characteristics of the SWCNT suspensions were not affected by changes to aggregation state, except when the centrifugation time was short and aggregation excessive. On the other hand, selective adsorption of nanotubes on the agarose matrix is confirmed by modifying the surfactant structure around the SWCNTs 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 SWCNT suspensions suggest that surfactant orientation rather than the exposed regions on the surface of the nanotubes is the dominant factor in the adsorption process.