Doctor of Philosophy / Department of Chemical Engineering / Placidus B. Amama / The continued depletion of fossil fuels and concomitant increase in greenhouse gases have encouraged worldwide research on alternative processes to produce clean fuel. Fischer-Tropsch synthesis (FTS) is a heterogeneous catalytic reaction that converts syngas (CO and H₂) to liquid hydrocarbons. FTS is a well-established route for producing clean liquid fuels. However, the broad product distribution and limited catalytic activity are restricting the development of FTS. The strong interactions between the active metal catalyst (Fe or Co) and support (Al₂O₃, SiO₂ and TiO₂) during post-synthesis treatments of the catalyst (such as calcination at ~500°C and reduction ~550°C) lead to formation of inactive and unreducible inert material like Fe₂SiO₄, CoAl₂O₄, Co₂SiO₄. The activity of FTS catalyst is negatively impacted by the presence of these inactive compounds. In our study, we demonstrate the use of a modified photo-Fenton process for the preparation of carbon nanotube (CNT)-supported Co and Fe catalysts that are characterized by small and well-dispersed catalyst particles on CNTs that require no further treatments. The process is facile, highly scalable, and involves the use of green catalyst precursors and an oxidant. The reaction kinetic results show high CO conversion (85%), selectivity for liquid hydrocarbons and stability. Further, a gaseous product mixture from FTS (C1-C4) was utilized as an efficient feedstock for the growth of high-quality, well-aligned single-wall carbon nanotube (SWCNT) carpets of millimeter-scale heights on Fe and (sub) millimeter-scale heights on Co catalysts via chemical vapor deposition (CVD). Although SWCNT carpets were grown over a wide temperature range (between 650 and 850°C), growth conducted at optimal temperatures for Co (850°C) and Fe (750°C) yielded predominantly SWCNTs that are straight, clean, and with sidewalls that are largely free of amorphous carbon. Also, low-temperature CVD growth of CNT carpets from Fe and Fe–Cu catalysts using a gaseous product mixture from FTS as a superior carbon feedstock is demonstrated. The efficiency of the growth process is evidenced by the highly dense, vertically aligned CNT structures from both Fe and Fe–Cu catalysts even at temperatures as low as 400°C–a record low growth temperature for CNT carpets obtained via conventional thermal CVD. The use of FTS-GP facilitates low-temperature growth of CNT carpets on traditional (alumina film) and nontraditional substrates (aluminum foil) and has the potential of enhancing CNT quality, catalyst lifetime, and scalability. We demonstrate growth of SWCNT carpets with diameter distributions that are smaller than SWCNTs in conventional carpets using a CVD process that utilizes the product gaseous mixture from Fischer-Tropsch synthesis (FTS-GP). The high-resolution transmission electron microscopic (HR-TEM) and Raman spectroscopic results reveal that the use of a high melting point metal as a catalyst promoter in combination with either Co (1.5 nm ± 0.7) at 850ºC or Fe (1.9 nm ± 0.8) at 750ºC yields smaller-diameter SWCNT arrays with narrow diameter distributions. Scalable synthesis of carbon nanotubes (CNTs), carbon nanofibers (CNFs), and onion like carbon (OLC) in a batch reactor using supercritical fluids as a reaction media is demonstrated. The process utilizes toluene, ethanol, or butanol as a carbon precursor in combination with ferrocene that serves as a catalyst precursor and a secondary carbon source. The use of supercritical fluids for growth does not only provide a route for selective growth of a variety of carbon nanomaterials, but also provides a unique one-step approach that is free of aggressive acid treatment for synthesis of CNT-supported metallic nanoparticle composites for catalysis and energy storage applications.

Magister Scientiae - MSc / The spectroscopic, SEM and Raman measurements on carbon nanotubes under the exact conditions of which OES analysis were made showed that at a pressure of 400 Torr and a flow rate of 200 sccm, the quality and quantity of single-walled carbon nanotubes was the highest. / South Africa

This thesis comprises detailed experimental and theoretical investigations of the transport properties of one-dimensional nanostructures. Most of the work is dedicated to the exploration of the fascinating effects occurring in single wall carbon nanotubes (SWCNT). These particular nanostructures gained an overwhelming interest in the past two decades due to its outstanding electronic and mechanical features. We have investigated the properties of a novel family of carbon nanostructures, named here as Y-shaped rings. The studies show that they present very interesting quantum interference effects. A high structural stability under tensile strain and elevated temperatures is observed. Within the semi-classical potential adopted, the critical strain values of structure rupture lie in the same range of their pristine SWCNT counterparts. This is directly verified by the first observations of these ring-like structures in a transmission electron microscopy. A merging process of asymmetric into symmetric rings is investigated in-situ under electron beam irradiation at high temperatures. The electronic properties of these systems are theoretically studied using Monte Carlo simulations and environment dependent tight-binding calculations. From our results, we address the possibility of double-slit like interference processes of counter-propagating electron waves in the ring-like structures. The nature of well defined, sharp peaks in the density of states are determined as the discrete eigenenergies of the central loop part. Furthermore, the formation and dispersion of standing waves inside the ring is shown to originate from the quantum-dot like confinement of each branch between the leads. The obtained dispersion relation is shown to be the same occurring in purely one-dimensional quantum dots of similar geometries. Furthermore, Fabry-Perot-like interferences are observed. We established at the IFW a bottom-up processing route to fabricate nanotube based electronic devices. The SWCNTs are grown by chemical vapor deposition and we present a detailed study of the different approaches to obtain individual nanotubes suitable for a successful integration into electronic devices. Wet-chemistry and ultra-thin films as well as ferritin were employed as catalyst particles in the growth of SWCNT samples. By adjusting the optimized process parameters, we can control the obtained yield from thick nanotube forests down to just a couple of free-standing individual SWCNTs. The nanotubes are localized, contacted by standard e-beam lithography and characterized at ambient- as well as liquid helium temperatures. We usually obtain quite transparent contacts and the devices exhibit metallic or a mixed metallic/semiconducting behavior. The well-known memory effect upon gate voltage sweeping as well as single electron tunneling in the Coulomb blockade regime are addressed.

In this thesis, bulk and local scale spectroscopic and microscopic tools have been applied to investigate the purified raw material of SWCNT and synthesized MWBNNT, BN-nanocapsules, B-doped SWCNT and SiC nanostructures. Using bulk scale sensitive techniques, including optical absorption spectroscopy, Raman spectroscopy, high-resolution electron energy-loss spectroscopy, the average response of the whole sample is obtained. On the other hand, on a local scale transmission and scanning electron microscopy as well as TEM-electron energy-loss spectroscopy provide information on single tubes or other nanostructures. First, diverse chemical and oxidation methods for the purification of as-produced SWCNT were presented. Purified samples were investigated using TEM and OAS. The analysis of the optical absorption spectra in the UV-Vis energy range revealed that some of the chemical treatments are harmful to nanotubes. In contrast to the chemical treatments an oxygen burning procedure was used on the raw material in high vacuum and a temperature range 450?650oC. The purification processes of SWCNT by HNO3 and oxygen burning procedures resulted in SWCNT comprised of selected diameters and a reduced diameter distribution. Both HNO3 and oxygen burning treatments can be used to selectively remove SWCNT with smaller diameters from the samples. In addition, an adapted substitution reaction was used for the synthesis of multiwall boron nitride nanotubes. It was shown that the IR-response of MWBNNT can be used as a fingerprint to analyse MWBNNT. As in h-BN for the analysis one has to be aware of the sample texture and the LO-TO splitting of the IR-active modes. TEM images and B1s and N 1s excitation edges of the grown material reveal the presence of multiwall BN nanotubes with an inner diameter of 3.1 nm and with a larger interplanar distance than in h-BN. The electronic properties of the multiwall BN nanotubes as derived from the q-dependent dielectric function e(w,q) are dominated by the band structure of the hexagonal-like BN sheets, as revealed by the large degree of momentum dispersion observed for the p and s+p plasmons, in agreement with that previously reported for different graphitic allotropic forms. Moreover, a fast and highly efficient synthesis route to produce BN nanocapsules with a narrow size distribution was developed. This was achieved by an adapted substitution process using SWCNT as templates followed by a rapid cooling treatment. The IR responses reveal the strong dipole active fingerprint lines of h-BN with distinct differences, which are due to texturing effects and which highlight the BN nanocapsules potential application as a reference source when deriving the sp2 to sp3 ratio in BN species due to their random orientation Furthermore, the idea of substitution was used for the systematic studies of B-doped SWCNT. The experiments carried out have resulted in 1, 5, 10, and 15 % boron incorporated into the single wall carbon nanotubes. Core level excitation spectroscopy of the B1s and C1s edges revealed that the boron atoms substitute carbon atoms in the tube lattice keeping an sp2-like bond with their nearest C neighbour atoms. Our results show that a simple rigid band model as has been applied previously to intercalated SWCNT is not sufficient to explain the changes in the electronic properties of highly doped B-SWCNT and a new type of a highly defective BC3 SWNT with new electronic properties is obtained. Finally, different silicon carbide nanostructures were produced. The spectroscopic and microscopic data led to a good understanding of the formation process. NH3 acts as a source of hydrogen that plays a key role in the formation of the structures through its ability to decompose SiC at high temperature such that along with the stacking faults that arise from the many polytypes of SiC the produced SiC nanorods become porous then hollow and eventually are completely decomposed.

Next generation polymer composites that utilize the high electrical conductivity and tensile strength of carbon nanotubes are of interest. To effectively disperse carbon nanotubes into polymers, a more fundamental understanding of the polymer/nanotube interface is needed. This requires the development of new analytical methods and techniques for measuring the adhesion between a single molecule and the sidewalls of carbon nanotubes. Atomic Force Microscopy is an integral tool in the characterization of materials on the nanoscale. The objectives of this research were to: 1) characterize the binding force between single molecules and the backbone of a single walled carbon nanotube (SWNT), and 2) measure and interpret the mechanical response of carbon-based nano-objects to compressive loads using an atomic force microscope. To identify chemical moieties that bind strongly to the sidewall of the nanotubes, two experimental approaches have been explored. In the first, force volume images of SWNT paper were obtained using gold-coated AFM tips functionalized with terminally substituted alkanethiols and para-substituted arylthiols. Analysis of these images enabled quantification of the adhesive interactions between the functionalized tip and the SWNT surface. The resultant adhesive forces were shown to be dependent upon surface topography, tip shape, and the terminal group on the alkanethiol. The mechanical response of several single- and multi-walled carbon nanotubes under compressive load was examined with an AFM. When the scanner, onto which the substrate has been mounted, was extended and retracted in a cyclic fashion, cantilever deflection, oscillation amplitude and resonant frequency were simultaneously monitored. By time-correlating cantilever resonance spectra, deflection and scanner motion, precise control over the length of nanotube in contact with the substrate, analogous to fly-fishing was achieved. This multi-parameter force spectroscopy method is applicable for testing the mechanical and interfacial properties of a wide range of nanoscale objects. This research has led to a clearer understanding of the chemistry at the nanotube/polymer interface, as well as the mechanical response of nanoscale materials. A new force spectroscopic tool, multi-parameter force spectroscopy, should be extremely helpful in characterizing the mechanical response of a myriad of nanoscale objects and enable nanoscale devices to become a reality.

Στόχος της διδακτορικής αυτής διατριβής ήταν η ανάπτυξη μιας μεθόδου παραγωγής νανοσωλήνων άνθρακα η οποία στηρίζεται στη χημική απόθεση ατμών, χρησιμοποιώντας ως πηγή του άνθρακα ενώσεις σε υγρή μορφή, όπως οι αλκοόλες. Επιπρόσθετα μελετήθηκαν διάφορες παράμετροι της πειραματικής διαδικασίας (πηγή άνθρακα, θερμοκρασία απόθεσης, είδος και συγκέντρωση μετάλλου και υποστρώματος, παρουσία υδρογόνου κ.ά), τόσο ως προς την επίδρασή τους στο ρυθμό εξέλιξης της διεργασίας, όσο και ως προς το είδος των παραγόμενων προϊόντων, με σκοπό τη στοχευμένη παραγωγή νανοσωλήνων άνθρακα με συγκεκριμένες ιδιότητες. Η κύρια πειραματική διάταξη αποτελούνταν από έναν θερμοβαρομετρικό αντιδραστήρα, ο οποίος επέτρεπε τη συνεχή μέτρηση των μεταβολών του βάρους του δείγματος σε συνάρτηση με το χρόνο, ενώ και φασματογράφος μάζας ήταν συνδεδεμένος στην έξοδο του αντιδραστήρα για να μελετηθεί η αέρια φάση των αντιδράσεων. Τα προϊόντα προκειμένου να πιστοποιηθούν ως προς το είδος των νανοσωλήνων που παρήχθησαν, χαρακτηρίστηκαν με τη βοήθεια ηλεκτρονικής μικροσκοπίας σάρωσης (SEM) και διερχόμενης δέσμης (TEM), καθώς και με φασματοσκοπία Raman και θερμοσταθμική ανάλυση (TGA). Τα αποτελέσματα των πειραμάτων οδήγησαν στο συμπεράσμα πως οι ατμοί της αιθανόλης είναι καλύτερη πηγή άνθρακα σε σύγκριση με της μεθανόλης, οδηγώντας μάλιστα στη παραγωγή μίγματος πολυφλοιϊκών και μονοφλοιϊκών νανοσωλήνων άνθρακα, με καθαρότητες που ξεπερνούσαν το 90%. Επιτακτική αποδείχθηκε η παρουσία του μετάλλου, το οποίο και αποτελεί το κέντρο πυρημοποιήσης για την ανάπτυξη των νανοσωλήνων, ενώ καθοριστική είναι και η χρήση υποστρώματος προκειμένου ο άνθρακας να αποτεθεί με τη μορφή αυτή. Επιπρόσθετα, η παρουσία του υδρογόνου αύξησε σημαντικά το ποσοστό του άνθρακα που αποτέθηκε οδηγώντας μάλιστα στο σχηματισμό μεταλλικών μονοφλοικών νανοσωλήνων άνθρακα πολύ μικρής διαμέτρου, η οποία υπολογίστηκε ίση με 0.45nm. / The main goal of this research was the development of a new method for the production of carbon nanotubes, based on chemical vapor deposition (CVD), which employs a liquid carbon source. In addition, a detailed investigation of the effect of several parameters (carbon source, deposition temperature, kind and metal concentration and support, hydrogen addition e.t.c.) on both the process and the final carbon product was carried out. For this purpose, a CVD experimental apparatus was developed, which uses vapors of liquid precursors and allows the continuously recording of sample weight changes in correlation with time. In some cases, a mass spectrometer was used as a way to determine the kind of processes that take place in the gas phase during carbon deposition. The solid product was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and thermogravimetric analysis (TGA). The experimental results led to the conclusion that ethanol vapors are preferable because they lead to higher yield of both multi-wall and single-wall carbon nanotubes. Also, it was proved that the presence of a metal catalyst and support is necessary, because the first one is the active site of carbon nanotubes formation, and the second leads to the deposition of carbon in this form. Additionally, it was proved that the use of hydrogen in the gas mixture of the process is very important, as a way to reduce catalyst, leading to the formation of metalic single-wall carbon nanotubes of very small diameter (0.45nm).

L’objectif de ce travail est d’élaborer des matériaux composites modèles nanotubes de carbone/polymères permettant de tirer profit des propriétés des nanotubes de carbone à l’échelle macroscopique. L’obtention de tels matériaux nécessitant une fonctionnalisation homogène entre les nanotubes de carbone et les polymères, les nanotubes de carbone utilisés doivent être individuels et de même réactivité chimique, donc de même diamètre. Ainsi, ils doivent être synthétisés par CVD par des nanoparticules catalytiques monodisperses et supportées. Dans la première partie, nous avons élaboré une nouvelle méthode générique de synthèse de nanoparticules d’oxydes métalliques supportées. Nous avons principalement détaillé la synthèse de nanoparticules de Fe2O3 dont la distribution en taille est de 1.1 ± 0.3 nm. Dans la deuxième partie, après avoir étudié la stabilité thermique de ces nanoparticules, nous les avons utilisées pour catalyser la croissance des nanotubes de carbone monofeuillets individuels par CVD. La caractérisation des nanotubes obtenus par Raman indique une distribution en diamètre exceptionnellement étroite de 1.27 ± 0.15 nm. Dans la troisième partie, nous avons tout d’abord étudié la mise en solution des nanotubes de carbone par fonctionnalisation non covalente avec un polymère hydrosoluble le POE portant un motif pyrène en bout de chaîne et mis en évidence un phénomène de déplétion qui limite la solubilisation des nanotubes. Nous avons ensuite élaboré des matériaux composites nanotubes de carbone/rrP3HT par fonctionnalisation covalente et non covalente et nous avons étudié l’efficacité de séparation de charge dans les deux cas de fonctionnalisations. / The aim of this work is to develop composite materials carbon nanotubes/polymers to take advantage of properties of carbon nanotubes at macroscopic scale. To get such materials, homogeneous functionalization between carbon nanotubes and polymers is required, carbon nanotubes must be individual with the same chemical reactivity, therefore the same diameter. Thus, they must be synthesized by CVD from monodispersed and supported catalyst nanoparticles. In the first part, we developed a new universal method for the synthesis of metal oxide supported nanoparticles. We mainly detailed the synthesis of Fe2O3 nanoparticles with size distribution of 1.1 ± 0.3 nm. In the second part, after studying the thermal stability of these nanoparticles, we used them to catalyze the growth of individual single wall carbon nanotubes by CVD. The caracterisation of the obtained nanotubes by Raman show exceptionally narrow diameter distribution of 1.27 ± 0.15 nm. In the third section, we first studied the dispersion of carbon nanotubes by noncovalent functionalization withhydro-soluble polymer POE with pyrene as end group and revealed depletion phenomena that limit the solubilization of nanotubes. Then we developed composite materials carbon nanotubes/rrP3HT by covalent and noncovalent functionalisation and we studied the efficiency of charge separation in both cases of functionalization.

The search and research for high performance materials for aerospace applications is a continuous evolving process. Among several fibre reinforced polymers, carbon fibre reinforced polymer (CFRP) is well known for its high specific stiffness and strength. Though high modulus and high strength carbon fibre with structural resin systems have currently been established reasonably well and are catering to a wide variety of aerospace structural applications, these properties are generally directional with very high properties along the fibre direction dominated by fibres and low in other directions depending mainly on the resin properties. Thus, there is a need to enhance the mechanical properties of the resin systems for better load transfer and to improve the resin dominated properties like shear strength and properties in directions other than along the fibre. Use of carbon nanotubes (CNTs) with their extraordinary specific stiffness and strength apparently has great potential as an additional reinforcement in resin for development of CNT-CFRP nanocomposites. However, there are several issues that need to be addressed such as compatibility of a particular resin with CNTs, amount of CNTs that can be added, uniform dispersion of these nanotubes, surface treatment and curing process etc., for optimal enhancement of the required properties. Epoxy and cyanate ester resin systems are finding applications in aerospace structures owing to their desirable set of properties. Of these, bisphenol E cyanate ester (BECy) resin of low viscosity with its low moisture absorption, better dimensional stability, and superior mechanical properties can establish itself as potential structural resin system for these applications. BECy in particular has the advantage of being more suitable for out of autoclave manufacturing process such as Vacuum Assisted Resin Transfer Molding (VARTM). Literature shows that, significant work has been carried out by various researchers reporting improvements using CNTs in epoxy resins along with various associated problems. However, studies on effects of addition of CNTs /fCNTs to BECy-CFRP composite system are not well reported. Thus, objective of this work is to study the effects of adding pristine and functionalized CNTs to low viscosity cyanate ester as well as epoxy resin systems. Further, to study the effects on mechanical properties of nanocomposites with carbon fibre reinforcement in these CNT dispersed resin system through a combination of experimental and computational approaches. Multiwall carbon nanotubes (CNTs) without and with different chemical functionalization are chosen to be added to epoxy and BECy resins. The quantity of these CNTs /fCNTs is varied in steps up to 1% by weight. Different methods of mixing such as shear mixing, ultrasonication and combined mixing cycles are implemented to achieve uniform dispersion of these nanotubes in the resin system. Standard test samples are prepared from these mixtures of nanotubes in resin systems to study the variation in mechanical properties. Further, these nanotubes added resin systems are used in fabricating CFRP laminates by VARTM process. Both uni-directional and bi-directional laminates are made with the above modified resin systems with CNTs/fCNTs. Series of experimental investigations are carried out to study various aspects involved in making of nanocomposites and the effects of the same on different mechanical properties of the nanocomposites. Standard specimens are cut out from these laminates to evaluate them for tension, compression, flexure, shear and interlaminar shear strength. The main parameters investigated are the effects of varied quantity of CNTs and functionalized CNTs in the resin mix and in CFRP nanocomposites, effect of different mixing / curing cycles etc. on the mechanical properties of the nanocomposites. The investigations have yielded very interesting and encouraging results to arrive at optimum quantity of CNTs to be added and also the effects of functionalization to achieve enhanced mechanical properties. In addition, correlation of mechanical property enhancements with failure mechanisms, dispersion behaviour and participation of CNTs / fCNTs in load transfer are explained with the aid of scanning electron microscope images. Computational studies are carried out through atomistic models using computational tools to estimate the mechanical properties, understand and validate the effects of various parameters studied through series of experimental investigations. An atomistic model is built taking into consideration the nanoscale effects of the single wall carbon nanotubes (SWCNTs) and its reinforcement in the BECy resin. Using these atomistic models, mechanical properties of individual SWCNT, BECy polymer resin, polymer with different quantities of added SWCNT, and the CFRP laminates with improved resin are computed. As the interaction of CNT with the polymer is only at the outermost layer and the mechanical properties of either MWCNTs or SWCNTs are too high compared to resin systems, it is not expected to have any difference in the final outcome whether it is MWCNT or SWCNT. Hence, only SWCNTs are considered in computational studies as it helps in reducing the complexity of atomistic models and computational time when coupled with polymer resin. This is valid even for functionalized CNT as functionalization is also a surface phenomenon. To start with, the mechanical behaviour of SWCNT is studied using molecular mechanics approach. Molecular mechanics based finite element analysis is adopted to evaluate the mechanical properties of armchair, zigzag and chiral SWCNT of different diameters. Three different types of atomic bonds, i.e., carbon-carbon covalent bond and two types of carbon-carbon van der Waals bonds are considered in the carbon nanotube system. The stiffness values of these bonds are calculated using the molecular potentials, namely Morse potential function and Lennard-Jones interaction potential function respectively and these stiffness values are assigned to spring elements in the finite element model of the SWCNT. The importance of inclusion of Lennard-Jones interactions is highlighted in this study. Effect of these non-bonded interactions is studied by making the numerical stiffness of these bonds to negligible levels and found that they significantly reduce the mechanical properties. The effect of non-bonded Lennard-Jones atomic interactions (van der Waal interactions) considered here is a novelty in this work which has not been considered in previous research works. The finite element model of the SWCNT is constructed, appropriate boundary conditions are applied and the behaviour of mechanical properties of SWCNT is studied. It is found that the longitudinal tensile strength and maximum tensile strain of armchair SWCNTs is greater than that of zigzag and chiral SWCNTs and its value increases with increasing SWCNT diameter. The estimated values of the mechanical properties obtained agree well with the published literature data determined using other techniques. As the systems become more complicated with the inclusion of polymers, molecular dynamics (MD) method using well established codes is more adoptable to study the effect of SWCNTs on BECy. Hence, it is used to model and solve the nanosystems to generate their stress-strain behavior. Further, MD approach followed here can effectively include interfacial interaction between polymer and the CNTs as well. Mechanical properties of SWCNT functionalized SWCNT (fSWCNT), pure BECy resin and that of the CNT nanocomposite consisting of specific quantity of SWCNT / fSWCNT in BECy are estimated using MD method. Atomistic models of SWCNT, fSWCNT, BECy, BECy with specific quantities of CNT / fSWCNT are constructed. A monomer of BECy is modelled and stabilized before its usage as a building block for modelling of BECy resin and to compute its properties. A cell of specific size containing monomers of BECy and another cell of same size with SWCNT at centre surrounded by BECy monomer molecules are built. The appropriate quantity of SWCNT in resin is modelled. This model captures the required density of the composite resin. The models so constructed are subjected to geometric optimization satisfying the convergence criteria and equilibrated through molecular dynamics to obtain a stable structure. The minimized structure is subjected to small strain in different directions to calculate the Young’s modulus and other moduli of the CNT-BECy resin composite. The process is repeated for different quantities of SWCNT in BECy resin to obtain their moduli. Further, tensile and shear strengths of CNT-BECy are obtained by subjecting the equilibrated structure to a series of applied strains from 0 to 10% in steps of 1%. The stress values corresponding to each strain are obtained and a stress – strain curve is plotted. From the stress- strain curve, the strengths of the CNT -BECy which is the stress corresponding to the modulus after which the material starts to soften are determined. Effects of functionalization on mechanical properties of SWCNT are observed. Further, effects of functionalization of SWCNT are studied with a specific quantity of fSWCNT on different moduli and strengths of BECy are investigated. The properties of enhanced CNT–BECy nanocomposite resin with different quantities of added CNT obtained through MD are used to estimate the mechanical properties of the CNT-BECy-CFRP nanocomposite using micromechanics model. Further, validation with experimental results is attempted comparing the trends in enhancement of properties of the CNT-BECy resin and CNT-BECy-CFRP nanocomposite system. The outcome of this research work has been significantly positive in terms of i) Development of an appropriate process establishing different parameters for dispersing CNTs in the resin system, mixing, curing cycle for making of nanocomposites demonstrating significant and consistent enhancement of mechanical properties of BECy based resin system and CFRP nanocomposites using optimum quantity of CNTs /fCNTs through a series of well planned and executed experimental investigations. Evaluation of mechanical properties for each of the cases has been carried out experimentally. ii) Establishing a computational methodology involving intricate atomistic modelling and molecular dynamics of nanosystems for estimation of mechanical properties of BECy polymer resin and to study the effects by addition of SWCNT / functionalized SWCNT on the properties. Results obtained through series of experimental investigations have been validated through this computational study. This could be an important step towards realising the potential of this resin system for high performance aerospace applications. Thus, in brief, detailed experimental work combined with computational studies performed as presented in this thesis resulted in achieving structurally efficient cyanate ester based nanocomposites which is unique and not reported in open literature.

Indiana University-Purdue University Indianapolis (IUPUI) / Carbon nanotubes (CNTs) are one of the most common nanoparticles (NP) found in workplace air. Therefore, there is a strong chance that these NP will enter the human body. They have similar physical properties to asbestos, a known toxic material, yet there is limited evidence showing that CNTs may be hazardous to human barrier epithelia. In previous studies done in our laboratory, the effects of CNTs on the barrier function in the human airway epithelial cell line (Calu-3) were measured. Measurements were done using electrophysiology, a technique which measures both transepithelial electrical resistance (TEER), a measure of monolayer integrity, and short circuit current (SCC) which is a measure of vectorial ion transport across the cell monolayer. The research findings showed that select physiologically relevant concentrations of long single-wall (SW) and multi-wall (MW) CNTs significantly decreased the stimulated SCC of the Calu-3 cells compared to untreated cultures. Calu-3 cells showed decreases in TEER when incubated for 48 hours (h) with concentrations of MWCNT ranging from 4µg/cm2 to 0.4ng/cm2 and SWCNT ranging from 4µg/cm2 to 0.04ng/cm2. The impaired cellular function, despite sustained cell viability, led us to investigate the mechanism by which the CNTs were affecting the cell membrane. We investigated the interaction of short MWCNTs with model lipid membranes using an ion channel amplifier, Planar Bilayer Workstation. Membranes were synthesized using neutral diphytanoylphosphatidylcholine (DPhPC) and negatively charged diphytanoylphosphatidylserine (DPhPS) lipids. Gramicidin A (GA), an ion channel reporter protein, was used to measure changes in ion channel conductance due to CNT exposures. Synthetic membranes exposed to CNTs allowed bursts of currents to cross the membrane when they were added to the membrane buffer system. When added to the membrane in the presence of GA, they distorted channel formation and reduced membrane stability.