Molecular Routes to Sorting Carbon Nanotubes

Abstract

Carbon nanotubes are molecular cylinders of graphene that are synthesized as heterogeneous mixtures consisting of an assortment of structures. Because the optical and electronic properties of nanotubes are strongly dependent on their atomic structure and bundling states, effectively dispersing and separating the nanotubes by the different structures is of great importance for their applications ranging from personal electronics and sensors to bioimaging and drug delivery systems.

In this thesis, we describe new molecular approaches to address the challenge of dispersing and sorting carbon nanotubes. First, an open-ring molecular container, acyclic cucurbit[n]uril, clips onto small diameter nanotubes stabilizing them in water leaving the remaining larger diameter nanotubes to agglomerate. At a concentration 1000 times lower than typically required for surfactants, these C-shaped molecules complex with carbon nanotubes creating large exposed surface areas along the tube outerwall. Simple addition of surfactant, sodium dodecylbenzene sulfonate, patches the exposed areas creating a nanotube fluorescent turn-on effect. A second approach to dispersing carbon nanotubes uses ammonium laurate, a previously unused surfactant though similar in structure to the popular sodium dodecylsulfate. When compared to sodium dodecylsulfate, we observe selectivity towards small diameter nanotubes and cleaner substrate deposition which is important for future applications. Lastly, a gel chromatography method is designed utilizing diazonium chemistry to improve the selectivity allowing nearly identical structures to be sorted in high purity. The surface chemistry disrupts the typical interaction between surfactant dispersed nanotubes and gel resin leading to differences in flow rates based on nanotube structure and therefore significantly improve the capability to sort nanotubes. Finally, we show that optical excitation of individual single-walled carbon nanotubes in the semi-dilute concentration regime is capable of melting double-stranded DNA on the excited nanotubes. These molecular approaches open new opportunities to dispersing and sorting carbon nanotubes in cleaner and highly selective manners.