Safe, lightweight, and cost-effective materials are required to practically store hydrogen for use in portable fuel cell applications. Compressed hydrogen and on-board hydrocarbon reforming present certain advantages, but their limitations must ultimately render them insufficient. Storage in hydrides and adsorption systems show promise in modeling and experimentation, but a practical medium remains unavailable. Since the earliest report of adsorption on single-walled carbon nanotubes (SWNT) in 1997, a number of controversial publications have claimed the hydrogen capacity of these materials to be between 0.1 to 10 wt. %. However, no study has yet demonstrated a plateau of adsorption with pressure that would verify the reported capacity. A volumetric adsorption measurement instrument was designed and constructed to resolve this controversy. The instrument is capable of degassing samples under high vacuum and offers unprecedented measurements of hydrogen storage up to a pressure of 300 atm and a broad range of temperatures. In addition, an electrical probe within the sample cell was designed to study the mechanism of adsorption in situ. The best hydrogen storage observed on bundles of purified SWNT was 1.6 wt. % at 264 atm and 200 K. At room temperature, a high-pressure plateau was found corresponding to an adsorption of 0.9 wt. % at a pressure of 300 atm, which equates to an adsorption to surface area ratio of 1.14 wt. %/l 000 m2/g. Contrary to the claim by the Caltech Group [Ye et al., 1999], resistance measurements of purified SWNT bundles revealed that bundles do not separate under high pressure. Instead, the bundles were found to compress under the action of external pressure, leading to an increase in conductivity with pressure. A simple geometrical model suggests that without this bundle separation the volume displaced by the sample may counteract the benefit gained by adsorption because of the increase in gas density at high pressure. The isosteric heat of adsorption on SWNT bundles was measured to be between 3.9 and 5.0 kJ/mol at low levels of adsorption, and the activation energy for adsorption determined by the Langmuir model was found to be 1.9 kJ/mol. These low energy parameters are indicative of weak physisorption. / Thesis / Master of Applied Science (MASc)

The discovery of nanotubes with unique mechanical, electrical, and thermal properties has led to their use in the development of the next generation of composite materials. However, their poor solubility and dispersion properties in any organic and aqueous solvents limits their potential applications. In order to improve their solubility, single-walled carbon nanotubes (SWNTs) were functionalized along their sidewalls with phenol groups using a 1,3-di^polar cycloaddition reaction. These phenols could be further derivatized with 2-bromoisobutyryl bromide, resulting in the attachment of atom transfer radical polymerization initiators to the sidewalls of the nanotubes. These initiators were found to be active in the polymerization of methyl methacrylate and t-butyl acrylate from the surface of the nanotubes. However, the polymerizations were not controlled, leading to the production of high molecular weight polymeric grafts with relatively large polydispersities. The resulting polymer carrying nanotubes were analyzed by IR, Raman spectroscopy, solid-state NMR, DSC, TEM, and AFM. The nanotubes functionalized with poly(methyl methacrylate) were found to be insoluble in organic solvents, such as THF and CH2CI2. However, the dispersion property of SWNTs in the polymer matrix was improved dramatically. Another monomer t-butyl acrylate (t-BuA) was also polymerized using the same macroinitiators. It was found that the SWNTs functionalized with t-BuA iii were soluble in a variety of organic solvents. The t-butyl groups of these appended polymers could also be removed to produce nanotubes functionalized with poly (acrylic acid), resulting in nanocomposites that are soluble in aqueous solutions. In addition, polystyrene (PS) which was prepared by stable free radical polymerization, was used to functionalize SWNTs through the radical coupling reaction. IR, NMR, TEM, and AFM confirmed that this polystyrene was covalently bonded to the SWNTs. It was also found that the resulting PS-SWNTs composites were quite soluble in organic solvents, such as THF and CH2C12. / Thesis / Master of Science (MSc)

Single-walled carbon nanotubes (SWNTs) are a new class of materials that have recently attracted a great deal of interest because of their unique structural, mechanical, and electronic properties. Also, SWNTs have a high potential for a number of technological applications, including molecular electronics, emissive devices, and photovoltaic devices. To fully utilize their unique properties, control of the solubility, processibility, and functionality of SWNTs is required. Therefore chemical functionalization of SWNTs using a variety of methods, in either covalent or noncovalent manner, has been developed to produce soluble nanotube composites coupled with various chemical moieties. To explore the possibility of making potential soluble nanotube-based materials for solar cells, SWNTs were functionalized with organic chromophore-labeled polymers via a radical coupling process. The organic chromophore was used to absorb light to produce photo-induced electrons, while the polymer chains were used for improving the solubility of SWNTs. These novel chromophore-labeled polymers were made by stable free radical polymerization (SFRP), either using a synthetic chromophore-functionalized styrenic monomer or by derivatizing well-defined polystyrenes. Specifically, the chromophores employed in this investigation were commercially available 7-hydroxycoumarin and coumarin-343. In order to carry out fluorescence studies of SWNT-coumarin composites systematically, various factors were probed by (1) altering polystyrene lengths between the SWNT and the coumarin; (2) changing the distribution of coumarins along the polymer chain, in the form of either a block or random copolymer; (3) placing single coumarins on the surface of SWNTs. All of these resulting polymer functionalized SWNTs were found to be soluble in certain organic solvents such as CHCl3. Different absorption behaviors have been observed for SWNTs functionalized with 7-hydroxycoumarin containing copolymers. Fluorescence was still observable for all of these composites, and the pi-pi interactions between coumarins and nanotubes were believed to be responsible for the broadening of emission bands of the resulting composites. / Thesis / Master of Science (MS)

The overall research theme of this dissertation was the study of nanoparticle/polymer composites. Two types of nanoparticles were utilized: Single-Walled Carbon Nanotubes and quantum dots. Chapter 1 of this thesis comprises an extensive literature review on Carbon Nanotubes, which presents theoretical aspects relevant to the structure and properties of CNTs, methods of purifying and solubilizing CNTs in aqueous and organic solvents and selected applications. This literature review is followed by the study and comparison of the optical limiting performances of different Single-Walled Carbon Nanotubes/conjugated polymer dispersions (Chapter 2). The results obtained are discussed in terms of dispersion of the SWNTs in the polymer solutions and resulting SWNT bundle diameters. Chapter 3 presents the spontaneous assembly of dendrimer patterns induced by SWNTs. Finally, chapter 4 presents a new method for fabricating quantum dot/polymer composites, which uses the extraction of positively charged quantum dot into a hydrophobic liquid. The resulting solution is used as a compatible polymerization medium for poly(methylmethacrylate ) networks enabling the formation of transparent and fluorescent composites. / Ph. D.

Single walled carbon nanotubes (SWNTs) are considered potential biomedical materials because of their flexible structure, hollow interior for fluidic transport, propensity for functionalization of the exterior walls, and biocompatibility. Research into exploiting these properties has focused on SWNTs as building blocks for novel drug-delivery systems, dosage forms, and biomedical substrates. However, the use of the internal nanochannels as conduits for trans-membrane drug delivery has not been explored. This research was initially designed to explore the latter.<p> It is postulated that due to their mechanical strength and the presence of an internal conduit, SWNTs can be used for nanofluidic transport. Using a magnetic field, the magnetically responsive SWNT are driven into intact stratum corneum, creating nanochannels, for trans-membrane drug delivery. Initial studies showed however that a bottleneck is the aggregation of SWNTs on the surface of stratum corneum. To achieve trans-membrane nanofluidic delivery, the SWNTs have to be well dispersed in an appropriate pharmaceutical medium, and the SWNT have to be of high purity. Similarly, the presence of impurities in SWNTs, and the dispersion state of these materials in pharmaceutical solvents may give an insight into the discrepancies in toxicity that is reported.<p> The purity of five commercially available SWNTs (AP-SWNT and P2-SWNT, from Carbon Solutions Inc, HMS-SWNT from Helix Materials, and NA-SWNT from Nanostructured and Amorphous Materials Inc. and CT-SWNT from ChepTubes Inc.) were analyzed by raman and electron dispersive x-ray spectroscopy (EDS) spectroscopy. Secondly, the dispersion states of SWNTs in various pharmaceutical solvents were evaluated by ultraviolet (UV) spectroscopy, scanning electron microscopy (SEM), dynamic light scattering (DLS), zeta potential, and Raman spectroscopy to identify potential agents for exfoliation of SWNTs in selected pharmaceutical solution.<p> SWNTs were dispersed in various solvents (water, propylene glycol [PG], dimethylsulfoxide [DMSO], and ethanol) as well as in 0.1% w/v aqueous solutions of anionic, cationic and neutral surfactants at a SWNT concentration of 0.1 mg/mL. SWNT suspensions described as dispersed yielded an evenly coloured suspension with no visible precipitate. The most stable dispersions were obtained with the gemini surfactants, which were confirmed by SEM observation of exfoliated SWNTs. Zeta (î) potential measurements of the fully dispersed SWNTs showed typical values of greater than +30 mV, while non-dispersed samples were less than +20 mV. SEM images of the dispersed solution showed the presence of exfoliated SWNTs compared to the aggregated SWNT clusters observed in non-dispersed systems. Raman spectra of dispersed SWNTs showed G-band peak shifts (to higher wavelengths), confirming the presence of exfoliated SWNTs.<p> Even though the purity of SWNT did not correlate with amount of SWNT in dispersion, exfoliation of bundled SWNTs was accompanied by an increase in UV absorbance of the dispersion, with maximum exfoliation determined by a relatively stable UV absorbance.<p> As pharmaceutical excipients, we have demonstrated that gemini surfactants are suitable dispersing agents for SWNTs, and shown that the dispersion of SWNT for gemini surfactants (12-3-12) is achieved below the critical micelle concentration. The dispersion of SWNT bundles into individual strands is the first crucial step towards their use in biological systems as drug carriers.

Single walled carbon nanotubes (SWNTs) are considered potential biomedical materials because of their flexible structure, hollow interior for fluidic transport, propensity for functionalization of the exterior walls, and biocompatibility. Research into exploiting these properties has focused on SWNTs as building blocks for novel drug-delivery systems, dosage forms, and biomedical substrates. However, the use of the internal nanochannels as conduits for trans-membrane drug delivery has not been explored. This research was initially designed to explore the latter.<p> It is postulated that due to their mechanical strength and the presence of an internal conduit, SWNTs can be used for nanofluidic transport. Using a magnetic field, the magnetically responsive SWNT are driven into intact stratum corneum, creating nanochannels, for trans-membrane drug delivery. Initial studies showed however that a bottleneck is the aggregation of SWNTs on the surface of stratum corneum. To achieve trans-membrane nanofluidic delivery, the SWNTs have to be well dispersed in an appropriate pharmaceutical medium, and the SWNT have to be of high purity. Similarly, the presence of impurities in SWNTs, and the dispersion state of these materials in pharmaceutical solvents may give an insight into the discrepancies in toxicity that is reported.<p> The purity of five commercially available SWNTs (AP-SWNT and P2-SWNT, from Carbon Solutions Inc, HMS-SWNT from Helix Materials, and NA-SWNT from Nanostructured and Amorphous Materials Inc. and CT-SWNT from ChepTubes Inc.) were analyzed by raman and electron dispersive x-ray spectroscopy (EDS) spectroscopy. Secondly, the dispersion states of SWNTs in various pharmaceutical solvents were evaluated by ultraviolet (UV) spectroscopy, scanning electron microscopy (SEM), dynamic light scattering (DLS), zeta potential, and Raman spectroscopy to identify potential agents for exfoliation of SWNTs in selected pharmaceutical solution.<p> SWNTs were dispersed in various solvents (water, propylene glycol [PG], dimethylsulfoxide [DMSO], and ethanol) as well as in 0.1% w/v aqueous solutions of anionic, cationic and neutral surfactants at a SWNT concentration of 0.1 mg/mL. SWNT suspensions described as dispersed yielded an evenly coloured suspension with no visible precipitate. The most stable dispersions were obtained with the gemini surfactants, which were confirmed by SEM observation of exfoliated SWNTs. Zeta (î) potential measurements of the fully dispersed SWNTs showed typical values of greater than +30 mV, while non-dispersed samples were less than +20 mV. SEM images of the dispersed solution showed the presence of exfoliated SWNTs compared to the aggregated SWNT clusters observed in non-dispersed systems. Raman spectra of dispersed SWNTs showed G-band peak shifts (to higher wavelengths), confirming the presence of exfoliated SWNTs.<p> Even though the purity of SWNT did not correlate with amount of SWNT in dispersion, exfoliation of bundled SWNTs was accompanied by an increase in UV absorbance of the dispersion, with maximum exfoliation determined by a relatively stable UV absorbance.<p> As pharmaceutical excipients, we have demonstrated that gemini surfactants are suitable dispersing agents for SWNTs, and shown that the dispersion of SWNT for gemini surfactants (12-3-12) is achieved below the critical micelle concentration. The dispersion of SWNT bundles into individual strands is the first crucial step towards their use in biological systems as drug carriers.

The design and performance of an instrument is presented whose purpose is the extraction of samples highly enriched in one species of single-walled carbon nanotubes from density gradient ultracentrifugation. This instrument extracts high purity samples which are characterized by various optical studies. The samples are found to be enriched in just a few species of nanotubes, with the major limitation to enrichment being the separation, rather than extraction. The samples are then used in optical and microscopic studies which attempt to determine the first absorption coefficient (S1) of the (6,5) species of nanotube. Initial experiments give a value of 9.2 ± 2.6 cm2 C atom-1. Future work is proposed to improve upon the experiment in an attempt to reduce possible errors

As pointed out more and more frequently in the literature, there is a pressing need for research into the health and environmental impact of nanoparticles. This work represents a joint effort between scientists in nanotechnology, chemistry and biology to answer this call and to investigate the environmental effects of carbon nantoubes (CNTs) from a brand new aspect. The results showed clearly the dose-dependent effects of single-walled carbon nanotubes (SWNTs) on the ingestion and digestion of bacteria by Tetrahymena thermophila, a ciliated protozoan, propagated to its prey bacteria, Escherichia coli. Investigated by confocal microscopy Tetrahymena were able to internalize large quantities of SWNTs and then excrete SWNTs and undigested bacteria in aggregates. Inhibition of ciliate bacterivory measured by Ciliate Bacterivory assay was evident at far below lethal concentrations. At high tube concentrations (above 6.8 μg∙ml-1), cell viability was affected. In addition, explored by fluorescence microscopy and scanning electron microscopy, SWNTs stimulated Tetrahymena to abnormally egest viable bacteria inside membrane protected structures, which enhanced bacterial survival during antimicrobial treatments, bacteriostatic or bacteriocidal. This phenomenon may have important implications to public health. In general, research on toxicity of nanoparticles is in a very early stage with most studies on direct fatality (kill or not to kill) of a single organism or certain type of cells. This work is believed to be among the first few investigating extrapolated effects. Hopefully, this wok will stimulate a line of research towards better understanding of the effects of nanomaterials on diverse organisms, and stimulate not only toxicology but also ecotoxicology studies.

As pointed out more and more frequently in the literature, there is a pressing need for research into the health and environmental impact of nanoparticles. This work represents a joint effort between scientists in nanotechnology, chemistry and biology to answer this call and to investigate the environmental effects of carbon nantoubes (CNTs) from a brand new aspect. The results showed clearly the dose-dependent effects of single-walled carbon nanotubes (SWNTs) on the ingestion and digestion of bacteria by Tetrahymena thermophila, a ciliated protozoan, propagated to its prey bacteria, Escherichia coli. Investigated by confocal microscopy Tetrahymena were able to internalize large quantities of SWNTs and then excrete SWNTs and undigested bacteria in aggregates. Inhibition of ciliate bacterivory measured by Ciliate Bacterivory assay was evident at far below lethal concentrations. At high tube concentrations (above 6.8 μg∙ml-1), cell viability was affected. In addition, explored by fluorescence microscopy and scanning electron microscopy, SWNTs stimulated Tetrahymena to abnormally egest viable bacteria inside membrane protected structures, which enhanced bacterial survival during antimicrobial treatments, bacteriostatic or bacteriocidal. This phenomenon may have important implications to public health. In general, research on toxicity of nanoparticles is in a very early stage with most studies on direct fatality (kill or not to kill) of a single organism or certain type of cells. This work is believed to be among the first few investigating extrapolated effects. Hopefully, this wok will stimulate a line of research towards better understanding of the effects of nanomaterials on diverse organisms, and stimulate not only toxicology but also ecotoxicology studies.

Two major projects involving the use of solution processed blended semiconductors for organic field effect transistors (OFET) were explored. The first incorporated unsorted single walled carbon nanotubes (SWCNTs) into a diketopyrrolopyrrole-quarterthiophene (DPP-QT) semiconductor to enhance the mobility of the OFET. 2 wt % SWCNT was found to be the optimal blend ratio, nearly doubling the device mobility (0.6 to 0.98 cm^2/V·s). Beyond this ratio, the metallic content of the SWCNT’s dropped the on/off ratio below acceptable levels. When source drain metals who’s work function poorly matched that of the DPP-QT semiconductors highest occupied molecular orbital (HOMO) were used, the SWCNT could dramatically reduce the charge injection ratio with best results achieved for Al, dropping the contact resistance from 10^5 to 45 MΩ. The second project explored the addition of small molecule additives into a UV-sensitive semiconductor 2,7-dipentyl[1]benzothieno[3,2-b][1] benzothiophene (C5-BTBT) mixed with a polymethyl methacrylate (PMMA) polymer binder. We generated a C5-BTBT based phototransistor sensitive to UV-A light. The HOMO and lowest unoccupied molecular orbital (LUMO) of C5-BTBT and the various additives were measured and discovered to play a critical role in how the device operates. We discovered if an additive has a LUMO lower in energy than C5-BTBT, it can act as a charge trap for a photogenerated electron. Electron deficient additives were found to retain a trapped electron for an extended period of time, allowing the device to remain in a high current state for an extended period of time (>1 hour). This provides an opportunity for the device to be used as an optical memory system or photoswitch. The best system could detect UV-A with a Pill > 10^5 and a photoresponsivity of 40 A/W at a Pinc of 0.0427 mW/cm^2. / Thesis / Doctor of Philosophy (PhD) / An emerging field of electronics is the use of organic materials that can be solution processed, to reduce manufacturing costs and make new and interesting products. Here we used unsorted carbon nanotubes blended into the semiconductor layer of a transistor, providing a bridge for the energy mismatch between the electrodes and the semiconductor. This allowed us the freedom to choose different metals to act as our electrodes when making electronic devices. Additionally through the correct choice of semiconductor, we added device functionality, making it responsive to UV-A light. This produced a device that could act as a UV-A sensor, logic switch or memory device. These devices are air stable and solution processable, a necessity if they are to be used in real world applications.