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January 2nd, 2008

Porphyrin and carbon nanotube assemblies in polar solvents

Abstract:
One of the chief obstacles to exploiting the useful electronic and materials properties of single-wall carbon nanotubes (SWCNTs) is their inclination to form ropes and bundles. Understanding the reaction paths involved in the transition from isolated SWCNTs to bundles in the presence of solvent is basic to controlling the process. Single- and multiple-wall carbon nanotubes (CNTs) in polar, or charged, solvents can also form aggregate assemblies and macromolecular complexes with porphyrin derivatives. This potential is of great interest, as the structural and optical properties of porphyrin derivatives and complexes can be easily engineered, a reality evident not just in the laboratory but also in nature. Indeed, in photosynthesis and other processes, the quantum mechanisms governing charge and energy transfer processes are fundamental to life.

Recent experiments investigating CNTs in amide solvents have led to the debatable conclusion that dispersion and partial debundling can be achieved at low nanotube concentrations with a variety of highly polar solvents possessing high surface tension.1 Among these, N-methylpyrrolidone (NMP) is considered to be the most effective. In particular, it has been postulated that at very low concentrations, the equilibrium (stable) state is a debundled one. Moreover, whether dispersion occurs appears to depend strongly on the method of sample preparation. Taken together, these results suggest that the debundled state is, in fact, not in equilibrium but is metastable (transient though relatively long-lived).

Source:
spie.org

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