Tomorrow’s lightweight, high-performance composite systems will be made of structures built with materials that have unprecedented intrinsic properties for performing a wide range of functions, such as EMI shielding, thermal management, flame resistance, lightning strike protection, acoustic damping, and health-monitoring. Current structures require parasitic components, e.g., metal strips, copper wire meshes, strain gauges, and heat sinks to provide these functions. By eliminating parasitic components, future high-performance multifunctional systems can achieve the intended objectives, while maintaining optimum weight, reliability, cost, and fuel efficiency. With the continuing growth of polymer composites in industries, such as aerospace, automotive, and wind energy, research and development on lightweight, high-performance composites that possess extraordinary properties for future multifunctional systems has generated considerable interest and excitement. Recent advances in nanomaterial synthesis and functionalization have shown that tailored property combinations are possible with reduced parasitic content to achieve multifunctionality. Cyanate ester (CE), a class of high-performance thermosetting resins (high T [subscript g], >250°C), has received considerable attention due to its good mechanical properties, thermal stability, flammability properties, ease of process, and volatile-free curing process. Multiwall carbon nanotubes were selected due to their unique combination of excellent mechanical, electrical, and thermal properties. The principal objective of this work is to determine the extent to which several different processing techniques will affect the MWNT dispersion and corresponding nanocomposite properties, such as thermal, flammability, mechanical, and electrical properties. A processing-structure-property relationship, as well as performance of this class of carbon-based CE nanocomposite, will be established. Therefore, a major scientific contribution of this study will be the development and characterization of a novel, multifunctional CE nanocomposite. Different mixing instruments, such as high shear mixer, ultrasonicator, planetary centrifugal mixer, etc. were used to disperse the nanotubes in the cyanate ester resin matrix. Microstructural morphology characterizations by SEM, STEM, and TEM show that various degrees of dispersions of MWNTs were obtained by the different mixing techniques. An attempt to quantify the MWNT dispersion was made. Electrical resistivity of samples processed by both stand mixer and three-roll mill passes the ESD requirement; however, the MWNT percolation thresholds by the two techniques are different. Thermal analysis shows that the addition of the Fe³+ catalyst or the coupling agent lowers the glass transition temperature and degrades the mechanical properties (e.g., storage modulus, tangent of phase angle delta) of the CE resin. On the other hand, processing techniques only affect the mechanical properties of the resin. Thermal stability of CE is only slightly affected by different processing techniques, as well as the addition of MWNTs. Much more significantly, flammability characterization shows that the incorporation of either the Fe³+ catalyst or the coupling agent substantially increases the peak heat release rate (PHRR) relative to the neat CE resin value. / text

Lead-tin solder has been widely used as interconnection material in electronics packaging for a long time. In response to environmental legislation, the lead-tin alloys are being replaced with lead-free alloys and electrically conductive adhesives in consumer electronics. Lead-free solder usually require higher reflow temperatures than the traditional lead-tin alloys, which can cause die crack and board warpage in assembly process, thereby impacting the assembly yields. The high tin content in lead-free solder forms tin whiskers, which has the potential to cause short circuits failure. Conductive adhesives are an alternative to solder reflow processing, however, conductive adhesives require up to 80 wt% metal filler to ensure electrical and thermal conductivity. The high loading content degrades the mechanical properties of the polymer matrix and reduces the reliability and assembly yields when compared to soldered assemblies. Carbon nanotubes (CNTs) have ultra high aspect ratio as well as many novel properties. The high aspect ratio of CNTs makes them easy to form percolation at low loading and together with other novel properties make it possible to provide electrical and thermal conductivity for the polymer matrix while maintaining or even reinforcing the mechanical properties. Replacing the metal particles with CNTs in conductive adhesive compositions has the potential benefits of being lead free, low process temperature, corrosion resistant, electrically/thermally conductive, high mechanical strength and lightweight. In this paper, multiwall nanotubes (MWNTs) with different dimensions are mixed with epoxy. The relationships among MWNTs dimension, volume resistivity and thermal conductivity of the composite are characterized. Different loadings of CNTs, additives and mixing methods were used to achieve satisfying electrical and mechanical properties and pot life. Different assembly technologies such as pressure dispensing, screen and stencil printing are used to simplify the processing method and raise the assembly yields. Contact resistance, volume resistivity, high frequency performance, thermal conductivity and mechanical properties were measured and compared with metal filled conductive adhesive and traditional solder paste.

Neste trabalho foram produzidos compósitos de nanotubos de carbono contendo nanopartículas de prata, os quais foram testados como substratos SERS (Surface-enhanced Raman Spectroscopy) na detecção do cristal violeta. Para obter tais compósitos foram necessárias modificações de nanotubos de carbono através de funcionalizações químicas para inserção de grupos carboxila e tiol, capazes de interferir no crescimento de nanopartículas metálicas através de um processo de redução térmica do acetato de prata sobre a superfície das amostras de nanotubo. Para a preparação de tais compósitos foram utilizadas duas amostras de nanotubos, uma de parede simples (SWNT) e outra de paredes múltiplas (MWNT) a fim de avaliar diferenças nos tamanhos e homogeneidade das nanopartículas formadas. Utilizou-se como ferramenta investigativa a espectroscopia Raman na caracterização destes compósitos, que forneceu informações sobre interação dos nanotubos de carbono com as nanopartículas de prata e mudanças estruturais ocasionadas durante a gama de funcionalizações. Para avaliar a morfologia dos compósitos foi utilizada a microscopia eletrônica de varredura (MEV) e a microscopia eletrônica de transmissão (TEM) que forneceram informações sobre o tamanho e a disposição das nanopartículas formadas através do tratamento térmico dos nanotubos com acetato de prata. Os compósitos preparados foram aplicados como substrato SERS na detecção do cristal violeta. Nesta aplicação foi avaliada a capacidade dos nanotubos em adsorver estas moléculas e o potencial do substrato na intensificação do espectro Raman do analito. Observou-se que a adsorção do cristal violeta sobre uma amostra de SWNT foi máxima após o tempo de 60 minutos de agitação. Já o substrato utilizado (SWNT-COOH@Ag) permitiu a detecção do cristal violeta em solução aquosa com concentração de até 1,0.10-8 mol.L-1. Utilizando o mapeamento Raman foi possível avaliar a presença do analito através do monitoramento de uma banda do espectro vibracional do analito intensificada pelo efeito SERS / In this work, we produced carbon nanotube composites containing silver nanoparticles, which were tested as SERS (Surface-enhanced Raman Spectroscopy) substrates in the detection of crystal violet. For these the synthesis of these composites modifications of the carbon nanotubes surface through chemical functionalizations were necessary for insertion of carboxyl and thiol groups, that can affect the growth of metal nanoparticles in thermal reduction process of silver acetate on the surface of the nanotube samples. For the preparation of such composites have single walled carbon nanotubes (SWNT) and a multi-walled carbon nanotubes (MWNT) to evaluate differences in size and homogeneity of the nanoparticles formed. Raman spectroscopy was used as an investigative tool in the characterization of these composites, which provided information on the interaction of carbon nanotubes with silver nanoparticles and structural changes ocurring during the range of functionalizations. To evaluate the morphology of the composites scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used. These techniques provided information about the size and assembly of the silver nanoparticles formed by heat treatment of the nanotubes with silver acetate. The nanotubes@Ag composites were applied as SERS substrates in the detection of crystal violet. In this application, we evaluated the ability of nanotubes to adsorb these molecules and the substrate potential in enhancing the Raman spectrum of the analyte. It was observed that the adsorption of the crystal violet on a sample of SWNT was maximal after 60 minutes of stirring. Substrate used (SWNT-COOH @ Ag) allowed detection of crystal violet in aqueous solution with a concentration as low as 1,0.10-8 mol.L-1. Using Raman mapping was possible to evaluate the presence of the analyte by monitoring a band of vibrational spectrum of the analyte enhanced by SERS effect.

Neste trabalho foram produzidos compósitos de nanotubos de carbono contendo nanopartículas de prata, os quais foram testados como substratos SERS (Surface-enhanced Raman Spectroscopy) na detecção do cristal violeta. Para obter tais compósitos foram necessárias modificações de nanotubos de carbono através de funcionalizações químicas para inserção de grupos carboxila e tiol, capazes de interferir no crescimento de nanopartículas metálicas através de um processo de redução térmica do acetato de prata sobre a superfície das amostras de nanotubo. Para a preparação de tais compósitos foram utilizadas duas amostras de nanotubos, uma de parede simples (SWNT) e outra de paredes múltiplas (MWNT) a fim de avaliar diferenças nos tamanhos e homogeneidade das nanopartículas formadas. Utilizou-se como ferramenta investigativa a espectroscopia Raman na caracterização destes compósitos, que forneceu informações sobre interação dos nanotubos de carbono com as nanopartículas de prata e mudanças estruturais ocasionadas durante a gama de funcionalizações. Para avaliar a morfologia dos compósitos foi utilizada a microscopia eletrônica de varredura (MEV) e a microscopia eletrônica de transmissão (TEM) que forneceram informações sobre o tamanho e a disposição das nanopartículas formadas através do tratamento térmico dos nanotubos com acetato de prata. Os compósitos preparados foram aplicados como substrato SERS na detecção do cristal violeta. Nesta aplicação foi avaliada a capacidade dos nanotubos em adsorver estas moléculas e o potencial do substrato na intensificação do espectro Raman do analito. Observou-se que a adsorção do cristal violeta sobre uma amostra de SWNT foi máxima após o tempo de 60 minutos de agitação. Já o substrato utilizado (SWNT-COOH@Ag) permitiu a detecção do cristal violeta em solução aquosa com concentração de até 1,0.10-8 mol.L-1. Utilizando o mapeamento Raman foi possível avaliar a presença do analito através do monitoramento de uma banda do espectro vibracional do analito intensificada pelo efeito SERS / In this work, we produced carbon nanotube composites containing silver nanoparticles, which were tested as SERS (Surface-enhanced Raman Spectroscopy) substrates in the detection of crystal violet. For these the synthesis of these composites modifications of the carbon nanotubes surface through chemical functionalizations were necessary for insertion of carboxyl and thiol groups, that can affect the growth of metal nanoparticles in thermal reduction process of silver acetate on the surface of the nanotube samples. For the preparation of such composites have single walled carbon nanotubes (SWNT) and a multi-walled carbon nanotubes (MWNT) to evaluate differences in size and homogeneity of the nanoparticles formed. Raman spectroscopy was used as an investigative tool in the characterization of these composites, which provided information on the interaction of carbon nanotubes with silver nanoparticles and structural changes ocurring during the range of functionalizations. To evaluate the morphology of the composites scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used. These techniques provided information about the size and assembly of the silver nanoparticles formed by heat treatment of the nanotubes with silver acetate. The nanotubes@Ag composites were applied as SERS substrates in the detection of crystal violet. In this application, we evaluated the ability of nanotubes to adsorb these molecules and the substrate potential in enhancing the Raman spectrum of the analyte. It was observed that the adsorption of the crystal violet on a sample of SWNT was maximal after 60 minutes of stirring. Substrate used (SWNT-COOH @ Ag) allowed detection of crystal violet in aqueous solution with a concentration as low as 1,0.10-8 mol.L-1. Using Raman mapping was possible to evaluate the presence of the analyte by monitoring a band of vibrational spectrum of the analyte enhanced by SERS effect.

The graphitic nature, continuous structure, and high mechanical properties of carbon nanotubes (CNTs) make them good candidate for reinforcing polymer fiber. The different types of CNTs including single-wall carbon nanotubes (SWNTs), few-wall carbon nanotubes (FWNTs), and multi-wall carbon nanotubes (MWNTs), and carbon nanofibers (CNFs) differ in terms of their diameter and number of graphitic walls. The desire has been to increase the concentration of CNTs as much as possible to make next generation multi-functional materials. The work in this thesis is mainly focused on MWNT and CNF reinforced polyacrylonitrile (PAN) composite fibers, and SWNT, FWNT, and MWNT reinforced poly(etherketone) (PEK) composite fibers. To the best of our knowledge, this is the first study to report the spinning of 20% MWNT or 30% CNF reinforced polymer fiber spun using conventional fiber spinning. Also, this is the first study to report the PEK/CNT composite fibers. The fibers were characterized for their thermal, tensile, mechanical, and dynamic mechanical properties. The fiber structure and morphology was studied using WAXD and SEM. The effect of two-stage heat drawing, sonication time for CNF dispersion, fiber drying temperature, and molecular weight of PAN was also studied. Other challenges associated with processing high concentrations of solutions for making composite fibers have been identified and reported. The effect of CNT diameter and concentration on fiber spinnability and electrical conductivity of composite fiber have also been studied. This work suggests that CNT diameter controls the maximum possible concentration of CNTs in a composite fiber. The results show that by properly choosing the type of CNT, length of CNTs, dispersion of CNTs, fiber spinning method, fiber draw ratio, and type of polymer, one can get electrically conducting fibers with wide range of conductivities for different applications. The PEK based control and composite fibers possess high thermal stability with almost no weight loss up to 500 degree C and negligible thermal shrinkage up to 200 degree C. The PEK based fibers showed high toughness which surpassed many of the high-performance fibers like Kevlar(R) and Zylon(R). The 10% FWNT containing fiber is unique in terms of high electrical conductivity and high toughness. The CNT based fibers may be used as structural material, fire-barrier/protection textile, electrode for electrochemical capacitor or fuel cells, and as a template for directional growth of tissues.

This research was designed to fabricate and characterize novel polyhedral phase segregated microstructures of polystyrene (PS)-matrix composites filled with multi-walled carbon nanotubes (MWNT) and indium tin oxide (ITO) nanopowders. PS-composites were compression molded with MWNT and ITO separately first. The resulting composites were conducting, and remained optically transparent. Mixtures of MWNT and ITO were then used to form mixed ITO/MWNT PS-composites in order to optimize their transparency and conductivity. This was achieved by fabricating composites with varying concentrations of fillers. Impedance spectroscopy was used to characterize the electrical properties of the PS-composites. Optical properties were characterized by measuring the transmission of light through the PS-composite in the visible light spectrum using a spectrophotometer. The electrical properties and microstructural attributes of the fillers used were also characterized. The main objective of the project was to understand the relationships between the structural, electrical, and optical properties of the PS-composites. The resistivity of PS-composites filled with MWNT ranged from 105 to 1013 Ω cm for samples with 0.007 to 0.9 vol% MWNT. The resistivity of PS-composites filled with ITO ranged from 107 to 1013 Ω cm for PS-composites with 0.034 to 0.86 vol% ITO. PS/ITO composites had a percolation threshold of 0.15, 0.25, or 0.3 phr ITO, depending on the type of ITO used in the composite. The percolation threshold of PS/MWNT composites was found to be 0.01 phr MWNT. Mixed ITO/MWNT PS-composites were already percolated, the concentrations investigated in xv ii this study were already above the percolation threshold of these composites. A time dependence on impedance was found for PS-composites filled with MWNT. As time increases there is a decrease in impedance, and in some cases also a dependence on voltage. All PS-composites showed a dependence on the microstructure of the PS matrix and the filler material. The resistivity and percolation threshold were lower for PS/MWNT composites than PS/ITO composites due to the difference in filler size and aspect ratio, since MWNT have a smaller size. The orientation of PS grains with respect to neighboring grains was found to affect the resistivity of PS/MWNT. PS/MWNT composites with preferentially oriented PS grains were found to have a lower resistivity. Mixed ITO/MWNT PS-composites with the right filler concentrations were able to maintain transmission while decreasing resistivity. The fracture surface of fractured PS-composites prepared in this work indicated that there was bonding between adjacent PS-grains. From this work, it can be concluded that large grain hybrid ITO/MWNT PS-composites provide insight into the effect of combining nanometer sized filler materials together in a polymer matrix on the resultant structural, electrical, and optical properties of the composite. In the future, it is recommended that this study be used to aid research in flexible transparent conducting electrodes using a polymer matrix and hybrid/mixed nanometer sized conducting fillers.

No description available.

No description available.

Les fluorures (NbF5, MoF6 et WF6) et les oxyfluorures (VOF3 et CrO2F2) de métaux de transition sont intercalés dans le graphite sous atmosphère oxydante de fluor. Ces composés (de second stade) sont utilisés en tant que précurseurs dans le but de réaliser un échange fluor-oxygène via un composé oxygéné à base de silicium: l'hexaméthyldisiloxane (HMDSO). Un mécanisme d'échange en deux étapes est proposé. Ces nouveaux matériaux présentent une réversibilité partielle vis a vis de l'intercalation électrochimique du lithium. De la même façon la réactivité des fluorures inorganiques (BF3, TiF4, NbF5, MoF6 et WF6) avec les nanotubes multiparois, élaborés par voie catalytique (Co/Al2O3), est étudié en présence de fluor. Le processus de purification suivant: traitement thermique et lavage acide est préalablement effectué. L'étude par DRX montre une intercalation partielle des nanotubes. En RPE, une modification des propriétés électroniques a pu être mise en évidence. La fluoration du [70] fullerène a une température de 320 °C, permet d'obtenir un matériau présentant une faible dispersion en composition. La liaison C-F est de type ionocovalente pour une longueur de 0,149 nm. Sa structure cristalline est cubique face centrée (cfc, a = 1,7949 nm). Les tests électrochimiques montrent, outre une défluoration de la molécule de C70, une intercalation réversible de lithium; ces deux phénomènes étant en compétition. La réduction de fluorures de graphite (covalents ou ioniques) par différentes méthodes (thermique, chimique et électrochimique) conduit à l'obtention de carbones désordonnés. Le stockage du lithium par voie électrochimique s'y effectue par l'intermédiaire de deux phénomènes situées à E < 0,2 V et à E > 0,8 V. Le premier est attribué à l'insertion du lithium entre les plans graphitiques ainsi qu'a l'adsorption de lithium dans les pores créés par le processus de réduction. A plus haut potentiel la dissociation des liaison Li-X de bord de plans conduit à une capacité supplémentaire.

The main motivation in this thesis is to compare the conformation and charge transport in conducting polymers and carbon nanotubes (CNTs) and to investigate those physical properties in their combined form of nanocomposites. It is known that both conducting polymers and carbon nanotubes are intrinsically 1-dimensional systems which consist of delocalized π-electrons. However, the main difference between these is the fact that flexibility of conducting polymers can be varied depending on the extent of conjugation while CNTs are rigid. Hence a comparison of electronic properties as correlated to their morphology has been carried out and their individual role in nanocomposites is further studied. The thesis consists of 6 chapters and appendix. Chapter 1 consists of brief introduction of general properties of both conducting polymers, CNTs and their nanocomposites. Chapter 2 deals with the sample preparation and experimental techniques used for the work. Chapter 3 elaborates on the conformational / structural studies on the systems. Chapter 4 focuses on the transport measurements to study the electronic properties of the samples. Chapter 5 reveals the magnetic properties of these systems which can be applied in technological devices. And chapter 6 gives the conclusion and future directions of the work being done. Chapter 1: Nanocomposites represent a guest-host matrix consisting of easily processible functionalized conjugated polymer as host, incorporating carbon nanotubes as fillers with versatile electronic and magnetic properties, which provide a wide range of technological applications. The conformation, charge dynamics as well as magnetic properties of these conducting polymers and carbon nanotubes, and various aspects of transport mechanism and spin dynamics present in the nanocomposite matrix are studied and presented in a consistent framework. Chapter 2: The multiwall carbon nanotubes (MWNTs) are grown by thermal chemical vapor deposition (CVD). The MWNTs are dispersed in solution of conducting polymers by ultrasonication and then the suspension is cast on glass substrate and slowly dried by moderate heating. Once dried completely, the free-standing films of thickness 15-25 μm are peeled off the substrate for measurements. The MWNTs, above a certain concentration, form an interconnected network in the 3-dimensional polymer matrix, following percolation mechanism. The disorder is brought into the system mainly by bundling of tubes and bundle intersections. The morphology and conformation of the samples are studied by SEM, TEM and small angle X-ray scattering (SAXS) techniques. Chapter 3: Small angle X-ray scattering (SAXS) studies in polymeric systems are carried out to probe local nanoscale morphology at various length scales to show the correlation among conformation and assembly of chains. Small angle X-ray scattering (SAXS) studies are carried out in poly [2-methoxy5-(2’–ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) solution of varying conjugation lengths as well as different solvents. By increasing the extent of πconjugation from 30 to 100 %, the persistence length increases by a factor of three. Moreover, a pronounced second peak in the pair distribution function is observed in fully conjugated chain, at larger length scales which indicates that the chain segments tend to self-assemble as the conjugation along the chain increases. The chain assembly and aggregation are further studied for suspensions of MWNTs in polyethylene dioxythiophene-polystyrene (PEDOT-PSS) with aqueous medium and DMSO (dimethyl sulphoxide). The SAXS profile of MWNT dispersion in aqueous PEDOT-PSS clearly show rigid-rod feature of the individual nanotubes evident by the q-1 behavior at short ranges. The crossover from q-1 to q-2 in the longer range further suggest that the suspension consists of individual nanotubes, nanotubes bundles and aggregates that give rise to a 3-dimensonal meshwork of intersecting tubes and ropes. For the MWNT dispersion in PEDOT-PSS with DMSO, however, such q-1 behavior is absent; which evidently shows that the rods are not isolated in the solution and are rather agglomerated. How these conformations affect the electrical and magnetic properties of these systems are studied further in Chapter 4. Chapter 4: Transport mechanism in single wall carbon nanotubes (SWNT), MWNT pellets, and nanocomposite films of MWNT and PEDOT-PSS is studied. The positive and negative magnetoresistance (MR) data in various SWNT samples are analyzed by taking into account the electron-electron interaction (EEI) contribution, in addition to the weak localization (WL) regime. The contribution from EEI to the total MR is confirmed from the universal scaling of MC relation showing that EEI plays a significant role at higher fields and lower temperatures. Intrinsic parameters like inelastic scattering length extracted for barely metallic sample follows the T-3/4 dependence due to inelastic electron-electron scattering in the dirty limit. Conductivity and magnetoresistance (MR) measurements on nanocomposite films with varying MWNT content (0.03 - 3 %) are performed at a field range 0-11 Tesla, and temperature range 1.3–300 K. The temperature dependence of resistance above 4 K suggests a Coulomb-gap variable range hopping (CG-VRH) transport in the network. Alhough solely negative MR (~ 5-6 %) is observed for pristine MWNT pellets; the nanocomposite films show a combination of large negative MR (~ 80 %) at T < 4 K, and a comparatively weaker positive MR (~ 30 %) for T > 4 K. This suggest that there are two mechanism interplaying and dominant at different temperature regimes which can be explained by the mechanism of transport of the charge carriers of MWNT intervened by that of the polymer matrix. In conclusion how the individual properties of conducting polymer and carbon nanotubes contribute to the unique electronic and conformational properties in their nanocomposites is framed in this investigation. Chapter 5: Magnetic properties of the pristine MWNTs as well as metal nanowires of nickel, nickel-iron (NiFe), nickel-iron-cobalt (NiFeCo) encapsulated in the MWNTs are studied using superconducting quantum interference device (SQUID) magnetometer. A typical example of Ni nanowires encapsulated in MWNT (Ni-MWNT) is taken and the results are compared to other forms of nickel (bulk, nanorod cluster, nanowire) to see the effect of size, shape and environment on the magnetic kproperties. The saturation magnetization and coercivity for Ni-MWNTs are 1.0 emu/gm and 230 Oe. The temperature dependence of magnetization indicates superparamagnetic which is supported by the field-cooled and zero-field-cooled plots determining a blocking temperature ~ 300 K. These altered magnetic properties of Ni-MWNTs are mainly due to the contribution from carbon nanotube encapsulation. Both the shape and environment enhance the total magnetic anisotropy of encapsulated nanowires at least by a factor of four. The encapsulation of metal nanowires in MWNTs tunes the magnetic properties of the system widely, e.g. from diamagnetic (pristine MWNTs) to paramagnetic (Ni-MWNT) to ferromagnetic (NiFe-MWNT) and a combination of para and ferro (NiFeCo-MWNT). Chapter 6: The conclusions of the different works presented in the thesis are coherently summarized in this chapter. Thoughts for future directions are also summed up. Appendix A: Spin dynamics in conducting polymer PEDOT-PSS in its pristine, processed with DMSO and nanocomposite form (with carbon nanotubes) is studied using solid state nuclear magnetic resonance (NMR). Plots of proton spin lattice relaxation times vs. temperature at a fixed frequency 23.4 MHz are compared to study the effect of the external agents on the polymer dynamics.