Interaction of Polymers with Single-Wall Carbon Nanotubes

Polymers are widely used for postsynthesis processing, purification, and individualization of single-wall carbon nanotubes (SWNTs) in aqueous or organic solvent environments. Here, the interaction of single-stranded DNA oligomers (ssDNA) and of a polyfluorene copolymer (F8T2) with (6,5) SWNTs was investigated from desorption kinetics and in the case of ssDNA also using adsorption isotherms. Eyring analysis of desorption rate constants reveals a linear increase of activation enthalpies with ssDNA oligomer length until Δ_desH^‡ saturates at (155 ± 5) kJ·mol^–1 for oligomers exceeding the ssDNA Kuhn length of about 6 nm. The Gibbs energy for desorption of Δ_desG^‡ = (96 ± 1) kJ·mol^–1 is length-independent because of entropy–enthalpy compensation. The saturation of desorption energies at the high polymer coverages studied here is attributed to incomplete adsorption with typically no more than a single Kuhn segment of a polymer attached to a SWNT.