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1. Fluorescence labeling and quantification of oxygen-containing functionalities on the surfaces of single walled and multi-walled carbon nanotubes. Nearly all applications of nanotubes (CNTs), from nanoelectronics to composites, require knowledge of the type and concentration of functionalities on the surface of the material. None of the methods conventionally used to characterize CNTs, such as Raman spectroscopy, IR spectroscopy, UV-VIS-NIR spectroscopy, and X-ray photoelectron spectroscopy, provide selectivity in identification together with sensitivity in quantification. Fluorescence labeling of surface species (FLOSS) to identify and quantify oxygen containing functionalities on single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) provides a solution that is reported in this dissertation. The high selectivity of covalent attachment combined with the sensitivity of the fluorescence measurements, allowed us reliably determine concentrations of aldehyde (together with ketone), alcohol, and carboxylic functional groups on as-produced and acid treated SWCNTs. The detection limit is as low as ~ 0.5 % at (1 in every 200 carbon atoms).(You never established the lower limit clearly) 2. Purification of carbon nanotubes by dynamic oxidation in air. The outstanding mechanical and electronic properties of carbon nanotubes make them promising materials for use in different areas of nanotechnology. However, the presence of impurities in as-produced nanotubes has been a major obstacle toward their industrial scale applications. Amorphous and graphitic carbon, and catalytic metal particles are the major impurities in raw carbon nanotubes. Isothermal oxidation of as-produced carbon nanotubes, followed by acid treatment, is the most commonly used purification strategy. The thermal oxidation step eliminates carbonaceous impurities and the acid treatment decreases the metal content. Unfortunately, most of the existing oxidation procedures either do not destroy all carbonaceous impurities or partially destroy carbon nanotubes as well. In the dissertation, a novel purification protocol via dynamic oxidation of as-produced single-walled carbon nanotubes (SWCNT) is reported. In the new procedure, carbon nanotubes are exposed to a wide range of temperatures during the heating ramp. The results of the purification of arc-produced and laser vaporization grown SWCNT using dynamic oxidation are presented. Purity analysis of dynamically oxidized samples by UV-VIS-NIR and Raman spectroscopy, as well as transmission electron microscopy, explicitly demonstrate that dynamic oxidation enables obtaining undamaged carbon nanotubes almost free of carbonaceous impurities. 3. Surfactant- free method of solubilization of non-functionalized single-walled carbon nanotubes in common solvents. One of the major factors that hamper the extensive use of carbon nanotubes (CNTs) in large-scale applications are related to the poor purity of CNTs, and the weak dispersibility of CNTs in the most common solvents. The presence of substantial impurities (sometimes up to 80% wt.) in as-produced CNTs almost obliterates the unique properties of the material. Furthermore, the difficulties with solubilization of CNTs slow down the processability of the material in potential applications. A new one-step method of making pure single-walled carbon nanotubes (SWCNTs) via the sequence of sonication cycles is described in the dissertation. Hours long stable solutions of SWCNTs in acetone, methanol and isopropanol of concentrations as high as ~ 15 mg/L were prepared using the procedure. The results of UV-VIS-NIR, Raman and Transmission Electron Microscopy suggest that SWCNTs were not destroyed or damaged by purification and solubilization processes. A possible physico-chemical explanation of the solublization mechanism is discussed. / Chemistry

<p> Electrochemical supercapacitors (ES) are urgently needed as components in many advanced power systems. The development of advanced ES is expected to enable radical innovation in the area of hybrid vehicles and electronic devices. Nanostructured manganese oxides in amorphous or various crystalline forms have been found to be promising electrode materials for ES. The use of composite electrodes of manganese oxide with carbon nanotubes is being proposed to improve the overall electrochemical performance of the ES.</p> <p> Electrodeposition methods have been developed for the fabrication of manganese oxide films with/without carbon nanotubes for applications in ES. Electrolytic deposition of manganese oxides was found to be possible using Mn2+ and Mn7+ species, co-deposition of multi wall carbon nanotubes (MWNT) and manganese oxide using cathodic electrosynthesis was successfully achieved.</p> <p> Novel chemical process has been developed for the synthesis of nano-size manganese oxide particles. Electrophoretic deposition of the nano-size manganese oxide particles was able to be performed in both aqueous and non-aqueous solutions. Electrophoretic co-deposition of the nano-size manganese oxide particles with carbon nanotubes was successfully achieved.</p> <p> The mechanisms and kinetics of all the deposition methods are discussed. Charge storage properties of the films prepared by different deposition methods are investigated and compared.</p> / Thesis / Master of Applied Science (MASc)

Single-walled carbon nanotubes (SWNTs) have attracted extensive research effort since their discovery nearly 30 years ago. Their impressive mechanical, optical, thermal, and electronic properties make them promising candidates for incorporation into a variety of applications. Depending on the method used for SWNT synthesis, different diameter ranges can be produced. Within these diameter ranges, a heterogeneous mixture of semiconducting and metallic species are present. The combination of these electronic species, as well as their minimal solubility in common solvents, hinders their incorporation into electronic devices, providing reasons for the development of scalable purification techniques. Although, some impactful purification strategies have been developed in recent literature, the use of conjugated polymers is considerably more scalable, less expensive, and offers processability of the final purified material. At the time of this thesis, the purification of semiconducting SWNTs has been realized using electron-rich conjugated polymers such as polyfluorenes, polycarbazoles, and polythiophenes. For metallic SWNTs, less progress has been made. When enriched, metallic SWNTs could act as an effective replacement for common metals in conductive applications. The objective of this work is to develop an efficient and scalable technique for the dispersion of metallic SWNTs and to shed light on the effect of polymer electronics on SWNT dispersion selectivity using nitrated poly(fluorene-co-phenylene)s and cationic poly(fluorene-co-pyridine)s. These investigations lead to the development of novel techniques using multiple conjugated polymers to yield enriched metallic SWNT samples. A secondary objective of this work is to investigate the gentle removal of the polymer, post-purification using UV-irradiation to cleave the polymer linkages of a poly(carbazole-co-terephthalate). Characterization of the polymer-SWNT composites is carried out using absorbance, photoluminescence, and Raman spectroscopy techniques to evaluate their electronic purity. / Thesis / Doctor of Philosophy (PhD)

A series of mixed matrix membranes based on zeolites incorporated into fluorinated polyimides were fabricated and characterized in this study. The first system consisted of a polyimide (6FDA-6FpDA-DABA) with carboxylic acid groups incorporated into its backbone and amine-functionalized zeolite particles (ZSM-2). FTIR indicated that these functional groups interacted with each other through hydrogen bonding. Both SEM and TEM images revealed good contact between the polyimide and the zeolite. Permeability studies showed a drop in He permeability suggesting there were no voids between the two components. While simple gases such as O2 and N2 followed effective permeabilities predicted by mixing theories, polar gases such as CO₂ did not. The second system fabricated used the same polyimide with amine-functionalized zeolite L. This zeolite differs from ZSM-2 in that zeolite L's pores are not clogged with an organic template, and it possesses 1-D pores as opposed to ZSM-2's 3-D pore structure. XPS and zeta potential experiments were performed to verify the presence of amine groups on the zeolite surfaces. FTIR data showed that after a heat treatment, amide linkages were created between the amine group on the zeolite and the carboxylic acid group of the polyimide. SEM images showed a good distribution of zeolite L throughout the polymer matrix, and no indication of voids between the two components. Permeability experiments were performed to determine if the addition of zeolite L to the polyimide improved its separation performance. The permeability was unchanged between the pure polyimide membrane and the mixed matrix membrane, suggesting there were no voids present within the matrix. Permeability results of larger gases followed a Maxwell Model. A third system was prepared using a poly(imide siloxane) (6FDA-6FpDA-PDMS) and untreated zeolite L. The primary focus of this investigation was to determine if the addition of the flexible segment would promote direct contact with the zeolite surface and remove the need to amine-functionalize the zeolite. Poly(imide siloxane)s were synthesized at 0, 22, and 41 wt % PDMS as verified using 1H-NMR. FTIR was employed to qualitatively verify the successful imidization of the polymers. SAXS patterns and TEM images did not reveal distinct phases indicative of phase separation, however, AFM images did show the presence of phase separation of the surfaces of the poly(imide siloxane)s. Permeability results showed a decrease in selectivity and an increase in permeability as the wt % of PDMS was increased. Permeabilities and selectivities dropped as the zeolite loading was increased from 0 to 20 wt %. Upon increasing the zeolite loading from 20 to 30 wt %, increases in permeability were observed, but both the permeability and selectivity were still below that of the pure polymer. The final system studied employed the 41 wt % PDMS poly(imide siloxane) as the polymer matrix and either closed-ended or open-ended carbon nanotubes as the filler. SEM images showed regions of agglomeration for both types of nanotubes. Helium permeability dropped in both types MMMs, but more so in closed-ended carbon nanotubes MMM. Nitrogen permeability was unchanged for the closed-ended carbon nanotubes MMM, and dropped slightly in the open-ended carbon-nanotube MMM. / Ph. D.

Elastic constants of single-walled carbon nanotubes (SWCNTs) and single-layer graphene sheets (SLGSs) are determined by studying their free vibration characteristics using molecular mechanics (MM) simulations with the MM3 potential and finding their equivalent continuum structures (ECSs). The computational framework has been validated by comparing the presently computed basal plane stiffness and frequencies of radial breathing modes (RBMs) with those available in the literature. We have considered armchair, zigzag and chiral SWCNTs of aspect ratios (length/ diameter in the unloaded relaxed configuration) ranging from 2 to 15. The wall thickness of ECSs of SWCNTs is determined by applying continuum theories, viz., beam, shell and 3D-linear elasticity to ECSs and equating their frequencies with those of SWCNTs obtained from the MM simulations. An expression for the wall thickness of an ECS of a SWCNT in terms of its chiral indices is deduced. The wall thickness of an ECS of a SWCNT is found to increase with an increase in its radius and to saturate at 1.37 Ã for the radius exceeding 15 Ã . Poisson's ratio for zigzag SWCNTs decreses with an increase in the tube radius, but that for armchair SWCNTs exhibits the opposite trend. For the same radius, Poisson's ratio of a chiral SWCNT is slightly more than that for an armchair tube but a little less than that for a zigzag tube. For zigzag SWCNTs, frequencies of inextensional modes of vibration saturate with an increase in the circumferential wave number but those of their ECSs do not. The MM simulations of uniaxial tensile deformations of SLGSs of aspect ratios (length/width) ~ 10 give the basal plane stiffness of ~ 340 N/m. The MM simulations of free vibrations of clamped SLGSs and the analysis of vibrations of their ECSs with a continuum theory gives a wall thickness of ~ 1 Ã for a SLGS. / Ph. D.

Carbon nanotubes (CNTs) are tubular structure of a layer or layers of carbon atoms. CNTs serve as a prototypical nanomaterial holding great promises for various basic and applied research applications in the fields of electrical, thermal, and structural materials owing to their superlative mechanical, thermal, electrical, optical, and chemical properties. Since the discovery of CNTs by Iijima in 1991, numerous researches have been conducted to quantify and understand the atomic origin of their high strength, exceptional thermal conductivity, and unique electrical properties. CNTs are also widely used as nanofillers in composite materials to enhance their mechanical properties such as fracture toughness and to serve as sensing agents. There is thus an imperative need to deeply understand the physical properties of CNTs and their responses to various models of deformations such as stretching, bending, twisting, and combinations thereof. In this thesis, we apply all-atom molecular dynamics simulations to study in detail the behavior of several single-walled, armchair CNTs under stretching and bending deformations, realized by imposing appropriate boundary conditions on the CNTs. The simulation results reveal unique scaling properties of the stretching and bending stiffness with respect to the CNT radius and length, which indicate that a single-walled CNT is best modeled as a thin cylindrical shell with a cross-sectional radius equal to the CNT radius and a constant wall thickness much smaller than the CNT radius. By studying the thermal fluctuations of carbon atoms on the CNT wall, the wall thickness is determined to be about 0.45~AA~for all the single-walled CNTs studied in this thesis and correspondingly, Young's modulus is estimated to be about 8.78 TPa for these CNTs. / Master of Science / Carbon atoms are magic building blocks of our world and the basis of life on the earth, and likely in the universe too. They can also form amazing materials with dimensionalities ranging from 0 to 3. For example, carbon atoms can form soccer-ball like spherical structures called fullerenes, with 0 dimensionality. They can also form 1-dimensional tubular structures with only one wall (i.e., one layer of carbon atoms) or multiple walls, called carbon nanotubes (CNTs) that have diameters typically in the nanometer range and lengths as long as 0.5 meter. Carbon atoms also form graphene sheets, which can be regarded as 2-dimensional structures, and 3-dimensional materials including graphite and diamond. In this work, we model CNTs using the molecular dynamics simulation method, where the motion of each atom is resolved and controlled if needed. Specifically, we study CNTs under stretching by fixing one end while pulling the other end in the axial direction, or bending by pulling the middle of a CNT along the radial direction in its cross-section while fixing its two ends. By fitting the simulation results to the continuum mechanics models, we show that a CNT is best described as a thin cylindrical shell with a radius equal to the CNT radius and a wall thickness much smaller than the radius. At the end, the wall thickness of all the CNTs studied here is determined to be about $0.45times 10^{-10}$ meter and their Young's modulus is estimated to be about $8.78times 10^{12}$ Pa, confirming that CNTs are one of the strongest and stiffest materials.

For many decades, fiber reinforced polymers (FRPs) have been extensively utilized in load-bearing structures. Their formability and superior in-plane mechanical properties have made them a viable replacement for conventional structural materials.  A major drawback to FRPs is their weak interlaminar properties (e.g., interlaminar fracture toughness). The need for lightweight multifunctional structures has become vital for many applications and hence alleviating the out-of-plane mechanical (i.e., quasi-static, vibration, and impact) and electrical properties of FRPs while retaining minimal weight is the subject of many ongoing studies. The primary objective of this dissertation is to investigate the fundamental processes for developing hybrid, multifunctional composites based on surface grown carbon nanotubes (CNTs) on carbon fibers' yarns. This study embraces the development of a novel low temperature synthesis technique to grow CNTs on virtually any substrate. The developed method graphitic structures by design (GSD) offers the opportunity to place CNTs in advantageous areas of the composite (e.g., at the ply interface) where conventional fiber architectures are inadequate. The relatively low temperature of the GSD (i.e. 550 C) suppresses the undesired damage to the substrate fibers. GSD carries the advantage of growing uniform and almost aligned CNTs at pre-designated locations and thus eliminates the agglomeration and dispersion problems associated with incorporating CNTs in polymeric composites. The temperature regime utilized in GSD is less than those utilized by other synthesis techniques such as catalytic chemical vapor deposition (CCVD) where growing CNTs requires temperature not less than 700 °C. It is of great importance to comprehend the reasons for and against using the methods involving mixing of the CNTs directly with the polymer matrix, to either fabricate nanocomposites or three-phase FRPs. Hence, chapter 2 is devoted to the characterization of CNTs-epoxy nanocomposites at different thermo-mechanical environments via the nanoindentation technique. Improvements in hardness and stiffness of the CNTs-reinforced epoxy are reported. Long duration (45 mins) nanocreep tests were conducted to study the viscoelastic behavior of the CNT-nanocomposites. Finally, the energy absorption of these nanocomposites is measured via novel nanoimpact testing module. Chapter 3 elucidates a study on the fabrication and characterization of a three phase CNT-epoxy system reinforced with woven carbon fibers. Tensile test, high velocity impact (~100 ms⁻¹), and dynamic mechanical analysis (DMA) were employed to examine the response of the hybrid composite and compare it with the reference CFRP with no CNTs. Quasi-static shear punch tests (QSSPTs) were also performed to determine the toughening and damage mechanisms of both the CNTs-modified and the reference CFRP composites during transverse impact loading. The synthesis of CNTs at 550 C via GSD is the focus of chapter 4. The GSD technique was adjusted to grow Palladium-catalyzed carbon filaments over carbon fibers. However, these filaments were revealed to be amorphous (turbostratic) carbon.  Plasma sputtering was utilized to sputter nickel nano-films on the surface of the substrate carbon fibers. These films were later fragmented into nano-sized nickel islands from which CNTs were grown utilizing the GSD technique.  The structure and morphology of the CNTs are evaluated and compared to CNTs grown via catalytic chemical vapor deposition (CCVD) over the same carbon fibers. Chapter 5 embodies the mechanical characterization of composites based on carbon fibers with various surface treatments including, but not limited to, surface grown CNTs. Fibers with and without sizing were subjected to different treatments such as  heat treatment similar to those encountered during the GSD process, growing CNTs on fabrics via GSD and CCVD techniques, sputtering of the fibers with a thin thermal shield film of SiO₂ prior to CNT growth, selective growth of CNTs following checkerboard patterns, etc. The effects of the various surface treatments (at the ply interfaces) on the on-axis and off-axis tensile properties of the corresponding composites are discussed in this chapter. In addition, the DMA and impact resistance of the hybrid CNT-CFRP composites are measured and compared to the values obtained for the reference CFRP samples. While the GSD grown CNTs accounted for only 0.05 wt% of the composites, the results of this chapter contrasts the advantages of the GSD technique over other methods that incorporate CNTs into a CFRP (i.e. direct growth via CCVD and mixing of CNTs with the matrix). Understanding the behavior of the thin CFRPs under impact loadings and the ability to model their response under ballistic impact is essential for designing CFRP structures.  A precise simulation of impact phenomenon should account for progressive damage and strain rate dependent behavior of the CFRPs. In chapter 6, a novel procedure to calibrate the state-of-the-art MAT162 material model of the LS-DYNA finite element simulation package is proposed. Quasi-static tensile, compression, through thickness tension, and in-plane Isopescu shear tests along with quasi-static shear punch tests (QSSPTs) employing flat cylindrical and spherical punches were performed on the composite samples to find 28 input parameters of MAT162. Finally, the capability of this material model to simulate a transverse ballistic impact of a spherical impactor with the thin 5-layers CFRP is demonstrated. It is hypothesized that the high electrical conductivities of CNTs will span the multifunctionality of the hybrid composites by facilitating electromagnetic interference (EMI) shielding. Chapter 6 is devoted to characterizing the electrical properties of hybrid CNT-fiberglass FRPs modified via GSD method. Using a slightly modified version of the GSD, denser and longer CNTs were grown on fiberglass fabrics.  The EMI shielding performance of the composites based on these fabrics was shown to be superior to that for reference composites based on fiberglass and epoxy. To better apprehend the effect of the surface grown CNTs on the electrical properties of the resulting composites, the electrical resistivities of the hybrid and the reference composites were measured along different directions and some interesting results are highlighted herein. The work outlined in this dissertation will enable significant advancement in protection methods against different hazards including impact, vibrations and EMI events. / Ph. D.