Since their discovery in 1991, carbon nanotubes, and especially single walled carbon nanotubes (SWNTs), have attracted significant attention due to their unique structural, mechanical, and electronic characteristics. Although many potential applications for carbon nanotubes have been suggested, several key obstacles currently preclude their practical commercial applications. One of these is their lack of solubility and processability. In order to address this issue, a number of covalent and non-covalent nanotube functionalization techniques have recently been reported in the literature. These methods allow for the manipulation of nanotube properties, such as their solubility, through the attachment of various chemical moieties. Although most of these methods involve covalent attachment of structures to either the ends or sidewalls of SWNTs, several examples of non- covalent functionalization have also been reported. Pyrene, with its flat and aromatic structure, has been shown to form strong pi-pi stacking interactions with the surface of SWNTs. With this in mind, we explored several methods towards SWNT solubilization with diblock copolymers through non-covalent polymer- nanotube interactions. Living free radical polymerizations (SFRP, ATRP) were employed to produce diblock copolymers with narrow polydispersity. Commercial and synthetic monomers with different functionalities could be utilized to produce polymers with varying properties. Specifically, we used polymers such as polystyrene, poly(methyl methacrylate), poly(t-butyl acrylate) and poly(acrylic acid) as one block of our diblock copolymers. The second block was composed of synthetic pyrene-functionalized monomers mixed with different amounts of monomers that match the composition of the first block. It was found that, upon mixing these diblock copolymers with insoluble nanotubes in various solvents, the nanotubes were partially solubilized through pi-pi stacking with the pyrene- containing blocks. / Thesis / Master of Science (MS)

Single-w ailed carbon nanotubes (SWNTs) were oxidatively shortened and functionalized with ruthenium-based olefin metathesis catalysts. These catalyst-functionalized nanotubes were shown to be effective in the ring-opening metathesis polymerization of norbornene, resulting in rapid polymerization from the catalyst sites on the nanotube. It was found that high polymer molecular weights could be reached, and the molecular weight increased linearly with polymerization time. The resulting polynorbomene-functionalized nanotubes were found to exhibit solubility in organic solvents, while the starting materials and catalyst-functionalized nanotubes were completely insoluble. The polymerized materials were characterized by NMR, IR, DSC, AFM and TEM. Polystyrene and poly[(t-butyl acrylate)-b-styrene] with well-defined molecular weights and polydispersities were prepared by nitroxide-mediated free-radical polymerization. The homo- and block-copolymers were used to functionalize shortened single-walled carbon nanotubes (SWNTs) through a radical coupling reaction involving polymer-centered radicals generated at 125°C via loss of the stable free-radical nitroxide capping agent. The resulting polymer-SWNT composites were fully characterized and were found to be highly soluble in a variety of organic solvents. This solubility could also be altered through chemical modification of the appended polymers. The t-butyl groups of appended PtBA-b-PS could be removed to produce poly[(acrylic acid)-b-styrene]- functionalized carbon nanotubes. The resulting composite was found to form aggregates in a mixture of chloroform/methanol (v/v: 1/1), as determined by dynamic light scattering (DLS). / Thesis / Master of Science (MS)

No description available.

Electronic applications have expanded to encompass a variety of materials. In particular, allotropes of carbon interest researchers for their electronic applications. Knowledge of carbon allotropes and their applications has expanded significantly since the discovery of C60 Buckminsterfullerene in 1985, the discovery of multi- and single-walled carbon nanotubes in the early 1990s, and the isolation of graphene in 2004. Single-walled carbon nanotubes (SWNTs) have the potential to bring next-generation electronic devices to fruition. Such devices could be flexible, conformable, and inexpensive. SWNT-based electronics are promising for chemical and biological sensing applications, for example, where high carrier mobilities are unnecessary, and material conformity and inexpensive processing are significant advantages. Considerable progress has been made in separating semiconducting SWNTs from metallic SWNTs, enabling SWNT incorporation into semiconducting electronic technologies. Selective sorting of semiconducting SWNTs using π-conjugated polymers is an effective and efficient technique to enrich large quantities of ultra-pure semiconducting SWNTs. Following semiconducting enrichment, SWNTs can be incorporated into electronic devices. This thesis focuses on the enrichment of semiconducting SWNTs via conjugated polymer extraction and incorporating the resulting polymer-SWNT dispersions into thin-film transistors (TFTs). Novel copolymers were investigated for their capacity to selectively sort and disperse large-diameter sc-SWNTs synthesized using the plasma torch technique. Absorption and Raman spectroscopy were employed to monitor the efficacy of the conjugated polymer extraction procedure. Following enrichment, the polymer-SWNT dispersions were incorporated into TFTs. The interaction between the conjugated polymer and the SWNT and the conjugated polymer and dielectric was an essential component of TFT optimization. Furthermore, the procedure of sorting and dispersing sc-SWNTs is investigated for its effect on TFT performance and was another component of TFT optimization. TFTs were electrically characterized in terms of carrier mobility, threshold voltage, hysteresis, and current on/off ratio. The film morphology of the SWNT TFTs was also investigated. Atomic force microscopy and Raman mapping were used to provide insight into the nanometre and micrometre scale film morphology, respectively.

The outstanding properties of carbon nanotubes (CNTs) have stimulated a large number of researches to explore the potential of using them as reinforcement in polymer composites. Although many studies have reported the enlighten improvement of the materials properties by using CNTs as reinforcement, there are no promising and optimal results have been concluded to date. This thesis aims at studying the mechanical properties on thermoset polymer, Epoxy, by employing a small amount of carbon nanotubes as reinforcement. Two different types of nanotube-based composites are prepared i.e. a raw single-walled carbon nanotube (SWNT) composites and a functionalized single-walled carbon nanotube (FSWNT) composite. Chemical functionalization on SWNTs with carboxyl functional group (COOH) aims at modifying the end caps of nanotubes, so to provide covalent bonding of SWNTs to the polymer matrix during manufacturing of composite systems. Different weight percentages (wt %) of each type of SWNTs are added into the composite system. Standard test methods are performed on these nanotube composite systems and satisfactory results were achieved when the weight percentages of both types of SWNTs increased. Through the comparison between two systems (raw SWNTs and FSWNTs), the FSWNT reinforced composite is found to provide a better improvement on the mechanical properties as compared with the SWNT reinforced system. The integrity of both composite systems is examined by using Scanning Electronic Microscopy (SEM). The SEM images of the composites indicated the derivation in wetting and bonding between the nanotubes (both SWNTs and FSWNTs) and epoxy resin, and the FSWNTs provide an eminent dispersion when compared with the SWNTs in the composite system. Moreover, thermal testings are employed to further investigate the interfacial interaction between the nanotubes and the polymer matrix. xiv Molecular Dynamics (MD) simulations are also carried out to investigate the structural change of a SWNT under different temperature-controlled manufacturing environments. Swivel of the SWNT was noticed as the temperature increased. Such alteration in structure form can provide physical interlocking between SWNT and its surrounding polymer system. Thus, its overall mechanical and thermal properties can be enhanced.

Single-Walled Carbon Nanotube (SWCNT) based Very Large Scale Integrated circuit (VLSI) interconnect is one of the emerging technologies, and has the potential to overcome the thermal issues persisting even with the advanced copper based interconnect. This is because of it’s promising electrical and thermal transport properties. It can be stated that thermal energy transport in SWCNTs is highly anisotropic due to the quasi one dimensionality, and like in other allotropes of carbon, phonons are the dominant energy carriers of heat conduction. In case of conventional interconnect materials, copper and aluminium, although their thermal conductivity varies over orders of magnitude at temperatures below100 K, near room temperature and above they have almost constant value. On the other hand, the reported experimental studies on suspended metallic SWCNTs illustrate a wide variation of the longitudinal lattice thermal conductivity (κl) with respect to the temperature(T)and the tube length(L)at low, room and high temperatures. Physics based analytical formulation of κl of metallic SWCNT as a function of L and T is essential to efficiently quantify this emerging technology’s impact on the rising thermal management issues of Integrated Circuits. In this work, a physics based diameter independent analytical model for κl of metallic SWCNT is addressed as a function of Lover a wide range of T. Heat conduction in metallic SWCNTs is governed by three resistive phonon scattering processes; second order three phonon Umklapp scattering, mass difference scattering and boundary scattering. For this study, all the above processes are considered, and the effective mode dependent relaxation time is determined by the Matthiessen’s rule. Phonon Boltzmann transport equation under the single mode relaxation time approximation is employed to derive the non-equilibrium distribution function. The heat flux as a function of temperature gradient is obtained from this non-equilibrium distribution function. Based on the Fourier’s definition of thermal conductivity, κl of metallic SWCNT is formulated and the Debye approximations are used to arrive at analytical model. The model developed is validated against both the low and high temperature experimental investigations. At low temperatures, thermal resistance of metallic SWCNT is due to phonon-boundary scattering process, while at high temperatures it is governed by three phonon Umklapp scattering process. It is understood that apart from form factor due to mass difference scattering, boundary scattering also plays the key role in determining the peak value. At room temperature, κl of metallic SWCNT is found to be an order of magnitude higher than that of most of metals. The reason can be attributed to the fact that both sound velocity and Debye temperature which have direct effect on the phonon transport in a solid, are reasonably higher in SWCNTs. Though Umk lapp processes reduce the κl steeper than 1/T beyond room-temperature, it’s magnitude is round1000 W/m/K upto 800 K for various tube lengths, which confirms that this novel material is indeed an efficient conductor of heat also, at room-temperature and above.

Carbon nanostructures have been extensively used in different applications; ranging from electronic and optoelectronic devices to energy conversion. The interest stems from the fact that covalently bonded carbon atoms can form a wide variety of structures with zero-, one- and two-dimensional configuration with different physical properties. For instance, while fullerene molecules (zero-dimensional carbon structures) realize semiconductor behavior, two-dimensional graphene shows metallic behavior with exceptional electron mobility. Moreover the possibility to even further tune these fascinating properties by means of doping, chemical modification and combining carbon based sub-classes into new hybrid structures make the carbon nanostructure even more interesting for practical application.  This thesis focuses on synthesizing SWCNT and different C60 one-dimensional structures as well as tuning their properties by means of different chemical and structural modification. The purpose of the study is to have better understanding of the synthesis and modification techniques, which opens for better control over the properties of the product for desired applications. In this thesis carbon nanotubes (CNTs) are grown by chemical vapor deposition (CVD) on iron/cobalt catalyst particles. The effect of catalyst particle size on the diameter of the grown CNTs is systematically studied and in the case of SWCNTs it is shown that the chirality distribution of the grown SWCNTs can be tuned by altering the catalyst particle composition. In further experiments, incorporation of the nitrogen atoms in SWCNTs structures is examined. A correlation between experimental characterization techniques and theoretical calculation enable for precise analysis of different types of nitrogen configuration in SWCNTs structure and in particular their effect on growth termination and electronic properties of SWCNTs are studied. C60 one-dimensional structures are grown through a solution based method known as Liquid-liquid interfacial precipitation (LLIP). By controlling the crystal seed formation at the early stage of the growth the morphology and size of the grown C60 one-dimensional structures where tuned from nanorods to large diameter rods and tubes. We further introduce a facile solution-based method to photo-polymerize the as-grown C60 nanorods, and show that such a method crates a polymeric C60 shell around the nanorods. The polymeric C60 shell exhibits high stability against common hydrophobic C60 solvents, which makes the photo-polymerized nanorods ideal for further solution-based processing. This is practically shown by decoration of both as grown and photo-polymerized nanorods by palladium nanoparticles and comparison between their electrochemical activities. The electrical properties of the C60 nanorods are also examined by utilizing a field effect transistor geometry comprising different C60 nanorods. In the last part of the study a variant of CNT is synthesized in which large diameter, few-walled CNTs spontaneously transform to a collapsed ribbon shape structure, the so called collapsed carbon nanotube (CCNT). By inserting C60 molecules into the duct edges of CCNT a new hybrid structure comprising C60 molecules and CCNT is synthesized and characterized. A further C60 insertion lead to reinflation of CCNTs, which eventually form few-walled CNT completely filled with C60 molecules.

Carbon nanomaterials have attracted significant attention in the past decades for their unique properties and potential applications in many areas. This dissertation addresses the preparation, functionalization and potential biomedical applications of various carbonaceous nanomaterials. Trimetallic nitride template endohedral metallofullerenes (TNT-EMFs, M₃N@C₈₀, M = Gd, Lu, etc.) are some of the most promising materials for biomedical applications. Water-soluble Gd₃N@C₈₀ was prepared by the functionalization with poly(ethylene glycol) (PEG) and hydroxyl groups (Gd₃N@C₈₀[DiPEG(OH)ₓ]). The length of the PEG chain was tuned by changing the molecular weight of the PEG from 350 to 5000. The 1H magnetic resonance relaxivities of the materials were studied at 0.35 T, 2.4 T and 9.4 T. Their relaxivities were found to increase as the molecular weight of the PEG decreased, which is attributed to the increasing aggregate size. The aggregate sizes were confirmed by dynamic light scattering. In vivo study suggested that Gd3N@C₈₀[DiPEG(OH)x] was a good candidate for magnetic resonance imaging (MRI) contrast agents. Another facile method was also developed to functinalize Gd₃N@C₈₀ with both carboxyl and hydroxyl groups by reaction with succinic acyl peroxide and sodium hydroxide thereafter. The product was determined to be Gd₃N@C₈₀(OH)~₂₆(CH₂CH₂COOM)~₁₆ (M = Na, H) by X-ray photoelectron spectrometry. The Gd₃N@C₈₀(OH)~₂₆(CH₂CH₂COOM)~₁₆ also exhibited high relaxivity, and aggregates in water. The research on both pegylated and carboxylated Gd₃N@C₈₀ suggests that aggregation and rotational correlation time plays an important role in relaxation, and the relaxivities and aggregation of the water-soluble metallofullerenes can be tuned by varying the molecular weight of the functionality. TNT-EMFs can be encapsulated inside single-walled carbon nanotubes (SWNTs) to form "peapod" structures by heating the mixture of TNT-EMFs and SWNTs in a vacuum. The peapods were characterized by Raman spectrometry and transmission electron microscopy (TEM). The peapods were then functionalized with hydroxyl groups by a high speed vibration milling (HSVM) method in the presence of KOH. The functionalized Gd-doped peapods exhibited high relaxivites and had an additional advantage of "double carbon wall" protection of the toxic Gd atoms from possible leaking. The HSVM method was modified by using succinic acyl peroxide. The modified HSVM method could functionalize multi-walled carbon nanotubes (MWNT) and single-walled carbon nanohorns (SWNHs) with carboxyl groups. In the presence of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC), carboxylate MWNTs and SWNHs could be conjugated with CdSe/ZnS quantum dots (QDs). TNT-EMFs were also encapsulated inside SWNHs to form SWNH peapods. SWNH peapods were functionalized by the modified HSVM method and then were conjugated with CdSe/ZnS QDs. The peapods were characterized by TEM. In vitro and in vivo studies indicated that SWNH peapods could serve as a multimodal diagnostic agent: MRI contrast agent (Gd₃N@C₈₀ encapsulated), radio-active therapeutic agent (Lu₃N@C₈₀ encapsulated) and optical imaging agent (QDs). / Ph. D.

Poly(lactic acid) is biodegradable polymer derived from renewable resources and non-toxic, which has become most interested polymer to substitute petroleum-based polymer. However, it has low glass transition temperature and poor gas barrier properties to restrict the application on hot contents packaging and long-term food packaging. The objectives of this research are: (a) to reduce coagulation of graphene oxide/single-walled carbon nanotube (GOCNT) nanocomposite in poly(lactic acid) matrix and (b) to improve mechanical strength and oxygen barrier property, which extend the application of poly(lactic acid). Graphene oxide has been found to have relatively even dispersion in poly(lactic acid) matrix while its own coagulation has become significant draw back for properties of nanocomposite such as gas barrier, mechanical properties and thermo stability as well as crystallinity. Here, single-walled carbon nanotube was hybrid with graphene oxide to reduce irreversible coagulation by preventing van der Waals of graphene oxide. Mass ratio of graphene oxide and carbon nanotube was determined as 3:1 at presenting greatest performance of preventing coagulation. Four different weight percentage of GOCNT nanocomposite, which are 0.05, 0.2, 0.3 and 0.4 weight percent, were composited with poly(lactic acid) by solution blending method. FESEM morphology determined minor coagulation of GOCNT nanocomopsite for different weight percentage composites. Insignificant crystallinity change was observed in DSC and XRD data. At 0.4 weight percent, it prevented most of UV-B light but was least transparent. GOCNT nanocomposite weight percent was linearly related to ultimate tensile strength of nanocomposite film. The greatest ultimate tensile strength was found at 0.4 weight percent which is 175% stronger than neat poly(lactic acid) film. Oxygen barrier property was improved as GOCNT weight percent increased. 66.57% of oxygen transmission rate was reduced at 0.4 weight percent compared to neat poly(lactic acid). The enhanced oxygen barrier property was ascribed to the outstanding impermeability of hybrid structure GOCNT as well as the strong interfacial adhesion of GOCNT and poly(lactic acid) rather than change of crystallinity. Such a small amount of GOCNT nanocomposite improved mechanical strength and oxygen barrier property while there were no significant change of crystallinity and thermal behavior found. / Master of Science

In this work, gadolinium-based carbon nanocapsules are developed as a novel nanotechnology that addresses the shortcomings of current diagnostic and therapeutic methods of stem cell-based cardiomyoplasty. With cardiovascular disease (CVD) responsible for approximately 30% of deaths worldwide, the growing need for improved cardiomyoplasty has spurred efforts in nanomedicine to develop innovative techniques to enhance the therapeutic retention and diagnostic tracking of transplanted cells. Having previously been demonstrated as a high-performance T1-weighted magnetic resonance imaging (MRI) contrast agent, Gadonanotubes (GNTs) are shown for the first time to intracellularly label pig bone marrow-derived mesenchymal stem cells (MSCs). Without the use of a transfection agent, micromolar concentrations of GNTs deliver up to 10^9 Gd(III) ions per cell, allowing for MSCs to be visualized in a 1.5 T clinical MRI scanner. The cellular response to the intracellular incorporation of GNTs is also assessed, revealing that GNTs do not compromise the viability, differentiation potential, or phenotype characteristics of the MSCs. However, it is also found that GNT-labeled MSCs exhibit a decreased response to select cell adhesion proteins and experience a non-apoptotic, non-proliferative cell cycle arrest, from which the cells recover 48 h after GNT internalization. In tandem with developing GNTs as a new stem cell diagnostic agent, this current work also explores for the first time the therapeutic application of the magnetically-active GNTs as a magnetic facilitator to increase the retention of transplanted stem cells during cardiomyoplasty. In vitro flow chamber assays, ex vivo perfusion experiments, and in vivo porcine injection procedures all demonstrate the increased magnetic-assisted retention of GNT-labeled MSCs in the presence of an external magnetic field. These studies prove that GNTs are a powerful ‘theranostic’ agent that provides a novel platform to simultaneously monitor and improve the therapeutic nature of stem cells for the treatment of CVD. It is expected that this new nanotechnology will further catalyze the development of cellular cardiomyoplasty and other stem cell-based therapies for the prevention, detection, and treatment of human diseases.