Document Type

Theses, Ph.D

Rights

This item is available under a Creative Commons License for non-commercial use only

Disciplines

2.10 NANO-TECHNOLOGY

Publication Details

Successfully submitted for the Award of Doctor of Philosophy to the Dublin Institute of Technology, August, 2010.

Abstract

Single-walled carbon nanotubes (SWCNTS) are proposed to be one of the most promising nanomaterials, with unique electronic and mechanical properties which lend themselves to a variety of applications. In all cases the quality of the SWCNT material is important, and for some applications it is paramount. Despite sustained efforts, all currently known SWCNT synthetic techniques generate significant quantities of impurities. They also grow in bundles or ropes and are largely insoluble in common organic solvents. SWCNTS can have a range of structures and their electronic properties (metallic or semiconducting) depend on their structure and as well on their diameters. Currently there is no production process that can produce only one particular type of SWCNTs. For these reasons, carbon nanotubes have been slow to reach maximum potential applications. To speed up the potential applications of SWCNTS it has now become mandatory to purify, increase the solubility, disperse and separate SWCNTs according to their electronic properties in a simplified and economical way. In this project polycyclic aromatic hydrocarbons (PAHs) of two oligomer series, namely the polyacene series and polyphenyl series, of systematically varied length, were used to selectively solubilise, disperse and separate SWCNTs produced by the pressure decomposition of carbon monoxide (HiPco) and arc discharge (AD) methods according to their electronic properties. The interactions and debundling of SWCNTs are investigated through a fluorescence based concentration dependent model. This model defines the concentration range where aggregated and isolated SWCNTs exist. If was found that regardless of the type of SWCNTs (HiPco of AD), the binding energy between SWCNTs and PAHS was the same and it increases as the molecular weight of PAHs increases, thereby establishing a linear relationship between binding energy of SWCNTs with PAHs and molecular weight of the corresponding PAHS, indicating the structure property relationship governing this solubilistion process. Atomic force microscopy was used to visualise the dispersed and isolated SWCNTs. To explore the selective solubilisation of SWCNTS with the aid of PAHS, Raman spectroscopy was used. From the Raman spectrosocopy study it was found that a broad range of HiPco and AD SWCNTs were solubilised with little evidence of true structural selectivity of HiPco SWCNTs. It can be stated that although the longer PAHS have the capacity to solubilise larger diameter SWCNTs due to their increased binding energy, in general a preference for smaller diameter SWCNTs were evident. This preference for smaller diameter nanotubes is reflected in the quantitative comparison of the solubilities of the two different types of SWCNTs, the smaller diameter HiPco SWCNTs being solubilised to a greater extent than the larger AD SWCNTs.