Dissertations / Theses on the topic 'Carbon nanotubes nanocomposite'

L’incorporation de nanotubes de carbone dans une matrice polymère permet d’obtenir des matériaux nanocomposites avec des propriétés exceptionnelles. Toutefois, ces dernières dépendent de l’état de dispersion et distribution des nanotubes dans la matrice. Afin de conférer de meilleures propriétés, il est essentiel que le procédé de synthèse des nanocomposites permette une répartition contrôlée des nanotubes dans la matrice. Un procédé de polymérisation in situ, en présence de nanotubes de carbone, a été choisi. Ce dernier permet de contrôler la répartition des nanotubes dans la matrice grâce à l’utilisation des ultrasons. Afin d’optimiser ce procédé, et notamment lors de la polymérisation anionique activée de l’e-caprolactame, l’influence de la présence des nanotubes sur la vitesse de polymérisation et les propriétés rhéologiques du milieu polymérisant a été déterminée. Grâce à une étude calorimétrique suivie d’une étude rhéocinétique, il a été démontré que la présence de nanotubes ralentit la polymérisation et augmente fortement la viscosité du milieu. Cette inhibition provient probablement d’une réaction entre les nanotubes et le catalyseur utilisé pour la polymérisation et dépend donc de l’état de dispersion des nanotubes dans la matrice, lequel peut ainsi être estimé par les études cinétiques. L’étude des propriétés rhéologiques et électriques des nanocomposites à matrice polystyrène et à renforts de nanotubes de carbone a également été entreprise. Suivant l’état de dispersion ainsi que les différents paramètres opératoires, les seuils de percolation électrique et rhéologique ont ainsi pu être déterminés
The introduction of carbon nanotubes into polymers leads to nanocomposite materials with exceptional properties. These later depend, however, on the dispersion and distribution of carbon nanotubes inside the matrix. A key objective, in nanocomposite preparation, is the set up of incorporation processes allowing a good state of dispersion of the nanotubes into the matrix. An in situ polymerization process, coupled with an ultrasound processor, was chosen to best fulfill this objective. The optimization of this process implies the knowledge of the evolution of reaction kinetics and rheological properties during the polymerization. The influence of carbon nanotubes on the anionic activated polymerization of e-caprolactam was investigated by calorimetric and rheokinetic studies. Carbon nanotubes were found to slow down polymerization kinetics and highly increase the viscosity after a certain conversion degree. This inhibition phenomenon could be produced by a reaction between carbon nanotubes and the catalyst employed for the polymerization reaction. The inhibition effect depended also on the state of dispersion of the nanotubes, consequently, kinetic and rheokinetic measurements are an indirect method to estimate the state of dispersion. The electrical and rheological properties of the nanocomposites were also investigated. The influence of the state of dispersion and other parameters, such as temperature, on the electrical and rheological percolation thresholds was identified

Dins de l’amplia gama de nanocompòsits, la incorporació de materials conductors de carboni nanoestructurats, entre els quals s’hi troben els nanotubs de carboni (NTCs) i el grafè, a dins d’una matriu polimèrica aïllant, és una forma molt atractiva de combinar les propietats mecàniques i elèctriques úniques del material de farciment amb els atributs dels plàstics. Concretament, els materials nanocompòsits basats en carboni han jugat un gran lideratge en el camp de l’electroquímica analítica, sobre tot en el desenvolupament de dispositius (bio)sensors, degut a les seves interessants avantatges respecte a un material conductor pur. Aquestes avantatges els hi proporcionen un alt valor afegit, com versatilitat, durabilitat, una fàcil regeneració de la superfície i integració, simplicitat a l’hora d’incorporar diferents (bio)modificadors o una baixa corrent de fons, entre d’altres. En aquest sentit, aquesta tesi aborda el desenvolupament de sensors nanocompòsits avançats de tipus amperomètrics que, havent sigut optimitzada la seva relació carboni/polímer, poden ser modificats amb un ampli ventall de nanopartícules (NPs) per millorar-ne la seva eficiència electroanalítica. Les propietats elèctriques d’aquests nanocompòsits i, per tant, la seva aplicabilitat analítica, es troben directament influenciades tant per la naturalesa de les partícules conductores com per la quantitat i distribució espacial de les mateixes a través de la matriu polimèrica aïllant. Una de les propietats electroquímiques més importants que envolten a aquests materials, és la similitud del seu comportament electroquímic amb el d’un array de microelèctrodes. Per tant, una optimització de la seva relació carboni/polímer respecte a la naturalesa del material conductor de partida, permetrà assolir una major dispersió de les àrees conductores a través de les zones no conductores, presentant així beneficis similars als d’un array de microelèctrodes. A més, és conegut que alguns paràmetres, tals com la resistivitat del material compost, la transferència electrònica, la robustesa del material i la corrent capacitiva es troben fortament influenciades per la naturalesa física de la mostra de nanotubs de partida, com és la seva relació longitud/diàmetre i la seva puresa, fet que poden influir fortament la resposta electroanalítica final del material transductor. Sota aquest context, la primera etapa de la Tesi va consistir en la implementació d’un conjunt de tècniques instrumentals que, aplicades de manera sistemàtica, han permès la caracterització i la optimització de la composició dels materials nanocompòsits basats en nanotubs de carboni i resina epoxi (Epotek H77) en relació a la naturalesa dels NTCs de partida per a la fabricació de sensors electroquímics més eficients. El protocol de caracterització dut a terme inclou eines elèctriques, electroquímiques, morfològiques, microscòpiques, espectroscòpiques i electro-analítiques. Un cop optimitzada les proporcions de CNT/epoxi, el següent pas va consistir en millorar el rendiment analític d’aquests sensors electroquímics nanocompòsits incorporant-ne diferents NPs per a la introducció d’algun tipus d’efecte electrocatalític. Per arribar a aquesta fita, es va desenvolupar una metodologia simple per a la síntesi d’una amplia gama de NPs. La Síntesi Intermatricial (IMS) va ser utilitzada com a tècnica verda per al disseny de tres rutes diferents que permetin una incorporació personalitzada d’aquestes NPs dintre del material transductor, obtenint així sensors amperomètrics més sensibles a diferents analits. Finalment, els estudis de caracterització i funcionalització implementats en els sensors nanocompòsits basats en NTCs han estat estesos a materials nanocompòsits basats en una altra forma al·lotròpica del carboni: el grafè, el qual és l’últim descobriment en termes de material de carboni nanoestructurat.
Entre la amplia gama de nanocompósitos, la incorporación de materiales conductores nanoestructurados de carbono, entre los que se encuentran los nanotubos de carbono (NTCs) y el grafeno, dentro de una matriz polimérica aislante, es una forma muy atractiva de combinar las propiedades mecánicas y eléctricas únicas del material de relleno con los atributos de los plásticos. Concretamente, los materiales nanocompósitos basados en carbono han jugado un gran liderazgo en el campo de la electroquímica analítica, sobre todo en el desarrollo de dispositivos (bio)sensores, debido a sus interesantes ventajas con respecto a un material conductor puro. Dichas ventajas les proporcionan un alto valor añadido, como versatilidad, durabilidad, fácil regeneración de la superficie e integración, simple incorporación de (bio)modificadores o baja corriente de fondo, entre otras. En este sentido, esta tesis aborda el desarrollo de sensores nanocompósitos avanzados de tipo amperométrico que, habiendo sido optimizada su relación carbono/polímero, pueden ser modificados con un amplio abanico de nanopartículas (NPs) para mejorar su eficiencia electroanalítica. Las propiedades eléctricas de estos nanocompósitos y, por lo tanto, su aplicabilidad analítica, están directamente influenciadas tanto por la naturaleza de las partículas conductoras como por la cantidad y distribución espacial de éstas a través de la matriz polimérica aislante. Una de las propiedades electroquímicas más importantes que envuelven a estos materiales es la similitud de su comportamiento electroquímico con respecto a un array de microelectrodos. Por lo tanto, una optimización de la relación carbono/polímero con respecto a la naturaleza del material conductor de partida permitirá lograr una mayor dispersión de las áreas conductoras a través de las zonas no conductoras, presentando beneficios similares a los de un array de microelectrodos. Además, es conocido que algunos parámetros, tales como la resistividad del material compuesto, la transferencia electrónica, la robustez del material y la corriente capacitiva están fuertemente influenciadas por la naturaleza física de la muestra de nanotubos de partida, como son su relación longitud/diámetro o su pureza, hecho que pueden influir fuertemente en la respuesta electroanalítica final del material transductor. Bajo este contexto, la primera etapa de esta tesis consistió en la implementación de un conjunto de técnicas instrumentales que, aplicadas de manera sistemática, han perimitido, la caracterización y optimización de la composición de materiales nanocompósitos basados en nanotubos de carbono y resina epoxi (Epotek H77) con respecto a la naturaleza de los NTCs de partida para la fabricación de sensores electroquímicos más eficientes. El protocolo de caracterización llevado a cabo incluye herramientas eléctricas, electroquímicas, morfológicas, microscópicas, espectroscópicas y electroanalíticas. Una vez optimizada las proporciones de NTC/epoxi, el siguiente paso consistió en mejorar el rendimiento analítico de estos sensores electroquímicos nanocompósitos incorporándoles diferentes NPs con la finalidad de introducir algún tipo de efecto electrocatalítico. Para alcanzar este objetivo, se desarrolló una metodología simple para la síntesis de una amplia gama de NPs. La Síntesis Intermatricial (IMS) fue utilizada como técnica verde para el diseño de tres rutas diferentes que permitan una incorporación personalizada de estas NPs en el material transductor, obteniendo así sensores amperométricos más sensibles a diferentes analitos. Finalmente, los estudios de caracterización y funcionalización implementados en los sensores nanocompósitos basados en NTCs han sido extendidos para materiales nanocompósitos basados en otra forma alotrópica del carbono: el grafeno, el cual es el último descubrimiento en términos de material de carbono nanoestructurado.
Among the wide range of nanocomposites, the incorporation of conducting nanostructured carbon materials, such as carbon nanotubes (CNTs) and graphene, into an insulating polymeric matrix is a very attractive way to combine the unique mechanical and electrical properties of individual filler with the advantages of plastics. Concretely, carbon–based nanocomposite materials have played a leading role in the analytical electrochemistry field, particularly in (bio)sensor devices, due to their interesting advantages regarding to a pure conductive material, such as versatility, durability, easy surface regeneration and integration, facile incorporation of a variety of (bio)modifiers or low background current, among others. Accordingly, this thesis tackles the development of advanced amperometric nanocomposite sensors that having been optimized regarding to carbon/polymer composition ratios, can be tunable with different types of nanoparticles (NPs) for improving their electroanalytical efficiency. The electrical properties of these nanocomposites and, therefore, their analytical applicability, are directly influenced by the conducting particles nature and the amount and spatial distribution of them through the insulating polymeric matrix. One of the most important electrochemical properties of these materials is the similarity of their electrochemical behavior with a microelectrode array. Thus, an optimization of the carbon/polymer ratio with respect to the nature of the conducting material will allow to achieve a greater dispersion of the conducting areas through the non-conducting areas, presenting similar benefits to the microelectrode array. In addition, it is known that some parameters, such as composite resistivity, heterogeneous electron transfer rate, material robustness and background capacitance current are strongly influenced by the physical nature of the raw CNT sample, such as their diameter/length ratio and purity, fact that may strongly influences the final electroanalytical response of the transducer material. Under this context, the first step of this thesis consisted of implementing a group of instrumental techniques that, systematically applied, have allowed the characterization and optimization of nanocomposite materials composition based on CNTs and epoxy resin (Epotek H77) in relation to the nature of the raw CNT sample for the fabrication of more efficient electrochemical sensors. The developed characterization protocol includes electrical, electrochemical, morphological, microscopic, spectroscopic and electroanalytical tools. Having been optimized the MWCNT/epoxy composition ratios, the next step consisted of enhancing the analytical performance of these electrochemical nanocomposite sensors introducing some electrocatalytical effect by the incorporation of different NPs. For this goal, a simple methodology for synthesizing a wide range of different NPs has been developed. Intermatrix Synthesis (IMS) has been used as a green technique to design three different routes for CNT/epoxy nanocomposite electrodes modification, which offer a customized way for the preparation of sensitive amperometric sensors. Finally, the characterization and functionalization studies applied for CNT–based electrochemical nanocomposite sensors have been extended for nanocomposite materials based on another allotropic form of carbon: the graphene, which is the last discovery in terms of nanostructured carbon material.

Multi-walled carbon nanotubes (MWNTs) are a nanofiller that has desirable multifunctional properties. They have been shown to offer improved mechanical, thermal, and electrical properties in composites. Research has been studying their incorporation into polymer composites. Polyamide 12 is a polyamide of interest that has been manufactured to have lower moisture absorption and higher ductility than other commercial polyamides such as 6 and 6,6 at room temperature. In these studies, MWNTs have been incorporated into polyamide 12 at different weight loadings and using MWNTs with differing outer diameters. The composites were melt processed and characterized using differential scanning calorimetry (DSC) to understand the effects of MWNTs on the crystallization behavior of polyamide 12. A melt peak splitting behavior was observed in the polyamide 12 and composite samples when the specimens were not allowed to fully anneal. Total crystallinity in the samples remained the same between the polyamide 12 and composites when the samples were fully annealed. Total crystallinity increased by 1 to 4 percent in the composites over the polyamide 12 when samples were not fully annealed. The addition of MWNTs to the polyamide 12 system increased the amount of crystallization contained in the lower temperature melting peak. An increase in MWNT concentration resulted in an increase in the crystallinity contained in the lower temperature peak. The addition of smaller diameter MWNTs resulted in a further increase in the lower temperature peak when the outer diameter was below a critical size.

Thesis (M.S.)--University of Cincinnati, 2007.
Advisor: Dr. Donglu Shi. Title from electronic thesis title page (viewed July 17, 2009). Includes abstract. Keywords: Carbon nanotubes; plasma functionalization; alumina; nanocomposite; quantum dots; in vivo imaging. Includes bibliographical references.

Projection Stereolithography (PSL) is an Additive Manufacturing process that digitally patterns light to selectively expose and layer photopolymer into three dimensional objects. Nanomaterials within the photopolymer are therefore embedded inside fabricated objects. Adding varying concentrations of multi-walled carbon nanotubes (MWCNT) to the photopolymer may allow for the engineering of an objects tensile strength and electric conductivity. This research has two goals (i) the fabrication of three-dimensional structures using PSL and (ii) the material characterization of nanocomposite photopolymers. A morphological matrix design tool was developed and used to categorically analyze published PSL systems. These results were used to justifying design tradeoffs during the design and fabricate of a new PSL system. The developed system has 300μm resolution, 45mm x 25mm fabrication area, 0.23mW/cm2 intensity, and 76.2mm per hour vertical build rate. Nanocomposite materials were created by mixing Objet VeroClear FullCure 810 photopolymer with 0.1, 0.2, and 0.5 weight percent MWCNT using non-localized bath sonication. The curing properties of these nanocomposite mixtures were characterized; adding 0.1 weight-percent MWCNT increases the critical exposure by 10.7% and decreases the depth of penetration by 40.1%. The material strength of these nanocomposites were quantified through tensile testing; adding 0.1 weight-percent MWCNT decreases the tensile stress by 45.89%, the tensile strain by 33.33%, and the elastic modulus by 28.01%. Higher concentrations always had exaggerated effects. Electrical conductivity is only measurable for the 0.5 weight-percent nanocomposite with a 8k/mm resistance. The 0.1 weight-percent nanocomposite was used in the PSL system to fabricate a three-dimensional nanocomposite structure.
Master of Science

Ce travail de thèse concerne l’étude de dispersions de nanotubes de carbone (NTC) dans une matrice polymère afin d’obtenir des matériaux nanocomposites avec des propriétés améliorées. Dans la première partie, nous nous sommes intéressés à l’enrobage des NTC par des copolymères à blocs amphiphiles afin de faciliter la dispersion en solution aqueuse. L’influence de la structure chimique, de la composition et de la masse molaire des copolymères sur les propriétés a été étudiée. Dans une deuxième partie, l’incorporation des NTC dans une matrice polymère a été développée. Des procédés par voie aqueuse et par voie fondue ont été choisis afin de contrôler la répartition des NTC dans une matrice modèle de polyoxyde d’éthylène ainsi que dans des de polyéthylène ou de polyméthacrylate de méthyle. L’étude des propriétés physiques, notamment rhéologiques et électriques des nanocomposites à renfort de nanotubes a été réalisée. Ainsi les relations entre l’état des dispersions, la nature de l’enrobage et le mode d’élaboration des composites ont été établies
This work is concerned with the study of carbon nanotubes (CNT) dispersions in a polymer matrix in order to obtain nanocomposite with unique properties. In the first part, we investigated the CNT wrapping by amphiphilic block copolymers to facilitate their suspension in aqueous solution. Based on the results, we could assess the effect on CNT dispersion quality of the molar mass of copolymers, the nature of the hydrophobic block and the length of hydrophilic block. In the second part, the incorporation of CNTs in polymer matrix was developed. Water or melt processing were chosen to control the distribution of CNTs in various polymer matrices (Polyethylene oxide, polyethylene and polymethyl methacrylate) through a prior wrapping of CNT. The studies of physical properties, including rheological and electrical properties, of nanocomposites were undertaken. Relationships between the state of dispersion, the nature of the coating and the method of preparation of composites were established

Cette thèse s’inscrit dans le cadre d’un projet GREENANONANO né d’un partenariat entre le Luxembourg Institute of Science and Technology (LIST), Goodyear et l’Université de Lorraine dans le but de relever un défi technologique concernant l’augmentation des performances des propriétés viscoélastiques de la gomme utilisée dans les pneumatiques. Cette gomme est un composite constitué d’un élastomère (caoutchouc naturel) renforcé par la silice et le noir de carbone. La dispersion de ces charges n’est pas optimale et tend à dégrader les propriétés mécaniques et électrostatiques et donc les performances des pneus. Faces à ces limitations industrielles, l’utilisation d’autres types de renforts tels que les nanotubes de carbone devient une alternative crédible. Etant donné que les nanotubes de carbone (NTCs) ont tendance à s’organiser en fagots, le problème de la dispersion reste à résoudre. Nous proposons dans cette thèse la mise en place d’un matériau biphasé constitué de silice mésoporeuse naturelle, appelée diatomite, sur laquelle ont été synthétisés des NTCs. La grande surface spécifique de la diatomite offre la possibilité d’y faire croître une grande densité de NTCs et d’accroître significativement la surface de contact avec la matrice polymère. Cette thèse multidisciplinaire a débuté par la synthèse de nanoparticules métalliques par ALD pour la croissance de NTCs, suivie d’un développement du procédé de croissance de NTCs sur la diatomite. L’intégration réussie des charges biphasées obtenues au sein de matrices polymériques (élastomère, thermoplastique) a permis de mesurer les propriétés mécaniques, thermiques et électriques des nanocomposites ainsi fabriqués
This thesis is part of the GREENANONANO project ensuing from a partnership between the Luxembourg Institute of Science and Technology (LIST), Goodyear Company and Université de Lorraine, in order to address a technological challenge for increasing tires performances. The latter are directly related to the viscoelastic properties of the rubber used in tires. This gum is a composite material made by mixing an elastomeric matrix (natural rubber) and fillers (silica and carbon black). Nowadays, the filler dispersion is not optimal, which degrades the mechanical and electrostatic properties and therefore performances of tires. All these industrial limitations require the use of other types of reinforcing agents such as carbon nanotubes. Since carbon nanotubes tend to be organized into bundles, the dispersion problem still exists. We therefore propose in this thesis the synthesis of a biphased material composed by diatomite particles (natural mesoporous silica) on which are grown carbon nanotubes (CNTs). The high surface area of diatomite offers the possibility of growing a high density of CNTs, increasing the contact area with the polymer matrix. This multidisciplinary thesis started with the synthesis of metal nanoparticles by Atomic Layer Deposition (ALD) to catalyse the growth of CNTs and then a process was developed to grow CNTs on diatomite particles. The successful integration of the resulting biphased particles in polymer matrices (elastomer, thermoplastic) allowed to measure the mechanical, thermal and electrical properties of the nanocomposites thus produced

This thesis presents the design of multifunctional structures through the optimal placement of nanomaterial additives. Varying the concentration of Carbon Nanotubes (CNTs) in a polymer matrix affects its local effective properties, including mechanical stiffness, electrical conductivity, and piezoresistivity. These local properties in turn drive global multifunctional performance objectives. A topology optimization algorithm determines the optimal distribution of CNTs within an epoxy matrix in an effort to design a set of structures that are capable of performing some combination of mechanical, electrical, or peizoresistive functions. A Pareto-Based Restart Method is introduced and may be used within a multi-start gradient based optimization to obtain well defined multiobjective Pareto Fronts. A linear design variable filter is used to limit the influence of checkerboarding. The algorithm is presented and applied to the design of beam cross-sections and 2D plane stress structures. It is shown that tailoring the location of even a small amount of CNT (as low as 2 percent and as high as 10 percent, by volume) can have significant impact on stiffness, electrical conductivity, and strain-sensing performance. Stiffness is maximized by placing high concentrations of CNT in locations that either maximize the bending rigidity or minimize stress concentrations. Electrical conductivity is maximized by the formation of highly conductive paths between electrodes. Strain-sensing is maximized via location of percolation volume fractions of CNTs in high strain areas, manipulation of the strain field to increase the strain magnitude in these areas, and by avoiding negative contributions of piezoresistivity from areas with differing net signed strains. It is shown that the location of the electrodes can affect sensing performance. A surrogate model for simultaneous optimization of electrode and topology is introduced and used to optimize a 2D plane stress structure. This results in a significant increase in sensing performance when compared to the fixed-electrode topology optimization.
Ph. D.
This dissertation presents a method that allows for the best placement of a limited amount of filler material within a base matrix material to form an optimal composite structure. Adding filler material, in this case Carbon Nanotubes, can change the effective behavior of the composite structure, enhancing the capabilities of the base matrix material by adding structural stiffness, electrical conductivity, and even the ability for the structure to measure its own strains. The degree to which these changes occur is dependent on the amount of filler material present in any given subsection of the structure. The method then is focused on determining how much of the filler to place in different subsections of the structure to maximize several measures of performance. These measures pertain to structural performance, electrical conductivity, and the structure’s ability to sense strains. Steps are taken within the method to remove non-physical designs and also to find the overall best design, called the global minima. The method is applied to several test structures of varying complexity, and it is shown that the optimization method can heavily influence performance by tailoring the filler material distribution. Further electrical and sensing performance gains can be obtained by properly selecting where the electrodes are located on the structure. This is demonstrated by including electrode placement in the design method along with the filler distribution.

Fiber and matrix-dominant properties of fiber-reinforced polymer composites are important in many advanced technological fields, such as aviation, aerospace, transportation, energy industry, etc. Still, pre-mixing the polymer matrix with nanoparticles may enhance the through-thickness or matrix-dominant properties, and surface treatment of fiber reinforcements with nanoparticles, on the other hand, may improve the in-plane or fiber-dominated properties of laminated composites, as well as interfacial adhesion. A novel manufacturing method that combines a spraying process with nanoparticle/epoxy mixture technique was introduced to incorporate carbon nanoparticles for enhancement of thermal properties of multiscale laminates. Several graphene-based nanomaterials including graphene oxide (GO), reduced graphene oxide (rGO), graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (MWCNTs) were employed to modify the epoxy matrix and the surface of glass fibers. Multiscale glass fiber-reinforced composites were fabricated from unmodified and modified epoxy, as well as fibers, using the vacuum-assisted resin transfer molding (VARTM) process. The composites obtained combined improvements in both the fiber and matrix- dominant properties, resulting in superior composites. The morphological, rheological, thermal and mechanical properties of the glass fiber-reinforced multiscale composites were investigated. The thermal properties of the epoxy/nanoparticle composites were studied through differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA) and thermal conductivity measurements. The tensile, bending, vibration, interlaminar shear strength (ILSS) and thermal characterization results indicated that the introduction of GNPs, GO, rGO, and MWCNTs enhanced the themo-mechanical properties. The fracture surfaces of the fiber-reinforced composites were examined by scanning electron microscopy (SEM) and the micrographs were analyzed to comment on the mechanical results.

Carbon nanotubes are known as ideal fillers for polymer systems; the main advantage of carbon nanotubes over other nano-reinforcing particles is the combination of superior strength and stiffness with large aspect ratio. Carbon nanotubes may improve the mechanical, electrical and thermal properties of polymers, but to realise their potential in polymer systems uniform dispersion, strong interfacial adhesion and alignment of nanotubes within the polymer matrix are necessary. These properties are not easy to achieve and they are key challenges in producing CNT/Polymer system. This research was carried out in an attempt to understand how the properties of CNT/Polymer composite can be optimised by manipulation of additives, compounding and postcompounding conditions. Polypropylene/Multi-Walled Carbon Nanotube (PP/MCNT) composites were prepared by conventional twin screw extrusion. Dispersants and compatibilisers were used to establish good interaction between filler and polymer. Several different extruder screw configurations were designed and the properties of PP/MCNT composite prepared by each configuration investigated. The results indicated that the addition of carbon nanotubes without additives enhanced mechanical, electrical and thermal properties of polypropylene polymer. Incorporation of compatibilisers into PP/MCNT improved the stiffness but decreased the strength of the nanocomposite, whilst addition of dispersants decreased the mechanical properties of the nanocomposite. Addition of both additives at high concentration improved electrical conductivity and induced electrical percolation in the nanocomposite. Extruder screw configuration was found to have significant effect on the electrical conductivity whilst only slightly affecting mechanical properties of the nanocomposite, possibly due to the competition between dispersion and degradation of polymer chains and possible reduction of carbon nanotube length by intensive shear during compounding. The use of screw configuration with high mixing intensity promoted the dispersion of nanotubes and favoured the conduction process in the nanocomposite. Finally in an attempt to improve dispersion and alignment of carbon nanotubes, compounded PP/MCNT composite was subjected to micromoulding, fibre spinning and biaxial stretching processes and the resultant properties investigated. Application of post-compounding process was found to have significant effect on mechanical and rheological properties of the nanocomposite. Stiffness and strength of the nanocomposites treated by post-compounding processes were found to increase by up to 160% and 300%, respectively. The reinforcement effect of carbon nanotubes in the stretched nanocomposites was found to be the greatest. Rheological analysis suggested that the application of post-compounding processes enhanced dispersion of carbon nanotubes within the nanocomposite. Overall, this finding of this research has shown that carbon nanotubes can be incorporated into polypropylene using conventional equipment to provide significant improvement in properties. By careful choices of additives, compounding and postcompounding conditions, specific properties can be further enhanced.

Molecular weights of 2,000, 6,000 and 10,000 of silane functionalized atactic polystyrene (aPS) and α,ω-divinyl functionalized polydimethylsiloxane (PDMS) were prepared via living anionic polymerization and bulk anionic ring opening polymerization respectively. Functionalization of the homopolymers was confirmed by FT-IR and 1H-NMR spectroscopy and their molecular weights were determined via 1H-NMR end group analysis. A hydrosilylation reaction between the functionalized homopolymers of different molecular weights produced nine polystyrene-block-polydimethylsiloxane-block-polystyrene (aPS-b-PDMS-b-aPS) triblock copolymers. Field emission scanning electron microscopy observations revealed the copolymers self-assemble into supramolecular structures. Dynamic Light Scattering measurements show only small increase in the order of nanometers of its hydrodynamic radius as the individual molecular weights of the homopolymers were increased. Nanocomposites of the copolymers were prepared by incorporating 1% of oxidized single walled carbon nanotubes (SWNTs) within the aPS-PDMS-aPS matrices via coagulation precipitation. Differential scanning calorimetry (DSC) thermal analysis shows the SWNT interacting with both aPS and PDMS constituting blocks. SWNTs interaction with aPS block either increases the polymer glass transition temperature (Tg) by restricting its segmental motion or decreases the Tg by a plasticization effect. Within the PDMS block the SWNTs act as nucleating sites accelerating the crystallization rate of the polymer. This is evident by the appearance of single and double melting endotherms in the DSC thermograms.

2011/2012
Nanotechnology underwent a very rapid development in the last decades, thanks to the invention of different techniques that allow reaching the nanoscale. The great interest in this area arises from the variety of possible applications in different fields, such as electronics, where the miniaturization of components is a key factor, but also medicine. The creation of smart systems able to carry out a specific task in the body in a controlled way, either in diagnosis or therapy or tissue engineering, is the ultimate goal of a newborn area of research, called nanomedicine. In fact, to reach such an outstanding objective, a nanometer‐sized material is needed and carbon nanotubes (CNTs) are among the most promising candidates. The aim of this thesis was to study this opportunity and, in particular, the possible application of carbon nanotubes for spinal network repairing. After a review of the main features of neuronal network systems and the most common techniques to study their functionality, possible applications of nanotechnology for nanomedicine purposes are considered, focusing the attention on CNTs as neuronal interface in nerve tissue engineering. The work can be divided into two big parts. In the first part the impact of carbon nanotubes on various neuronal systems was studied. Different form of carbonaceous materials (carbon nanotubes, nanohorns and graphene) were deposited in a homogeneous way on a glass surface playing with organic functionalization and different deposition techniques. Hippocampal neuronal cells were grown on their surface to better understand how morphology and conductivity of the material could influence the activity of the neuronal network evidencing how both these characteristics could affect the electrophysiological properties of neurons. Then, also spinal neurons were grown on carbon nanotubes network deposited on a glass substrate to evaluate, for the first time, the impact of carbon nanotubes on this kind of cells. The tight interaction between these two materials appeared to cause a faster maturation of the spinal neurons with respect II to the control grown on a glass substrate. The long-term impact on a complex tissue (spinal cord slice) grown on carbon nanotubes carpet was also studied. The intimate interaction between the two materials observed by TEM and SEM analysis caused an increase in dimensions and number of neuronal fibers that comes out from the body of a spinal cord slice. An increase in electrophysiological activity of all neuronal network of the slice was also reported. In the second part of the work different conductive biocompatible nanocomposite materials based on carbon nanotubes and “artificial” polymers (such as Nafion, PVA, PET, PEI, PDMS and PANI) were investigated. The idea is to test these materials as neuronal prosthesis to repair spinal cord damage. All the prepared scaffolds showed CNTs on the surface favoring CNTs-neurons interaction. To address this aim different techniques and different organic functionalizations of CNTs were utilized to control supramolecular interactions between the nanomaterial and polymers orienting the deposition of the CNTs and preventing their aggregation. After that, an innovative method to study the possible ability of this nanocomposite materials to transmit a neuronal signal between two portions of spinal cord was designed. Functionalization of gold surfaces with thiolated carbon nanotubes have been conducted in order to develop suitable devices for neuronal stimulation and consequent spinal cord lesions repairing. In particular thiol groups were introduced on the graphitic surface of carbon nanotubes by means of covalent functionalization. First of all, the interaction of CNTs with gold nanoparticles has been evaluated, then a gold surface has been coated by means of contact printing technique with a homogeneous film of CNTs. This hybrid material could be useful to produce innovative electrodes for neuronal stimulation
XXV Ciclo
1985

Le besoin de sources d’énergie autonomes connaît un regain d’intérêt de plus en plus important avec la multiplication des équipements portables et le développement des réseaux de capteurs. Au-delà de l’utilisation traditionnelle des batteries, il y a un intérêt évident à générer l’énergie électrique nécessaire au cœur du système lui-même en utilisant le gisement environnemental disponible : gradients thermiques, vibrations mécaniques….Ceci est également rendu possible par la réduction importante de la consommation des composants électroniques observés ces vingt dernières années. Parmi les dispositifs susceptibles d’exploiter le gisement vibratoire, les matériaux électro-actifs occupent une place de choix. Actuellement, on recherche des matériaux légers, pouvant se déposer sur des grandes surfaces et peu coûteux à la réalisation. Ceci ouvre des perspectives séduisantes à l’utilisation de polymères électro-actifs en lieu et place des matériaux céramiques piézoélectriques. Parmi les EAP disponibles, les polyuréthanes (PU) sont des élastomères thermoplastiques d'un grand intérêt pour une vaste gamme d'applications en tant que transducteurs ou actionneurs lorsque l'on considère leur importante déformation sous champ électrique, une énergie spécifique élevée, et leur réponse rapide De plus, ces matériaux sont légers, très souples, présentent de faibles coûts de fabrication, et peuvent être facilement moulés dans n'importe quelle forme souhaitable. Des travaux récents ont montré que l'énergie récoltée peut être augmentée en incorporant des nanotubes de carbone (NTC) dans une matrice de polyuréthane. Cependant, les nanocomposites peuvent ne pas avoir été optimisées, car il est bien connu que les NTC sont difficilement dispersées dans une matrice polymère et que la force d'adhérence interfaciale est généralement médiocre. Une solution pour améliorer à la fois la dispersion et l'adhérence peut consister en greffant des chaînes de polymère sur les surfaces de la NTC. L'objectif principal de cette thèse était de développer des polymères nanocomposites à haute efficacité pour la récupération d'énergie et d'actionnement. La motivation principal était d'utiliser des NTC greffé-polymère pour améliorer la dispersion, l'adhérence interfaciale dans PU, et de comprendre comment cela peut changer les propriétés électroactifs des nanocomposites PU / NTC. En d'autres termes, ce était un projet pluridisciplinaire, y compris une optimisation du processus d'élaboration, caractérisations physiques ˗ notamment les comportements de microstructure, électriques et mécaniques dans une large gamme de fréquences et températures ˗ et la détermination des propriétés électroactifs. Il s’agissait également de développer une modélisation des lois de comportements en s’aidant de l’analyse de la microstructure par imagerie
Harvesting systems capable of transforming dusty environmental energy into electrical energy have attracted considerable interest throughout the last decade. Several research efforts have focused on the transformation of the mechanical vibration into electrical energy. Most of these research activities deal with classical piezoelectric ceramic materials, but more recently, a promising new type of materials is represented by electroactive polymers (EAPs). Among the various EAPs, polyurethane (PU) elastomers are of great interest due to the significant electrical-field strains, and due to their attractive and useful properties such as flexibility, light weight, high chemical and abrasion resistance, high mechanical strength and easy processing to large area films as well as their ability to be molded into various shapes and biocompatibility with blood and tissues. In addition, it has recently been shown that the incorporation into a PU matrix of nanofillers, such as carbon nanotubes (CNTs), can greatly enhance the expected strain, or the harvested energy. However, it is well known that CNTs are hardly dispersed in a polymeric matrix, and that the interfacial adhesion strength is generally poor. An effective method to improves both dispersion and adhesion may consist in functionalizing CNTs by grafting polymer chains onto their surfaces. The main objective of this thesis was to develop high-efficiency polymers nanocomposites for harvesting energy and actuation. The key motivation was to use polymer-grafted CNTs to improve dispersion, interfacial adhesion in PU, and understand how this can change the electroactive properties of the PU/CNT nanocomposites. In other words, it was a pluridisciplinary project including an optimization of the elaboration process, physical characterizations ˗ including microstructural, electrical and mechanical behaviors in a wide range of frequencies and temperatures ˗ and the determination of the electroactive properties. A comprehensive study was then carried out first on pure PU to understand how their electroactive properties depend on their microstructure, and then on the nanocomposites to understand how the incorporation of functionalized CNT can improve the electromechanical properties

This thesis presents the study of nanocomposites based on immiscible polymer blend of polycarbonate and acrylonitrile-butadiene-styrene (PC/ABS) filled with multi-walled carbon nanotubes (MWCNT). The aim is to achieve an improvement of mechanical properties and electrical conductivity of the nanocomposites. In an initial stage, a twin-screw extruder was used to obtain nanocomposites by melt compounding. Three methods of carbon nanotubes addition were studied: direct addition, dilution from a masterbatch and feeding of MWCNT suspension in ethanol. For each method, the influence of nanofiller content and processing parameters on morphology and final properties of the nanocomposite was analyzed. Furthermore, the influence of two types of carbon nanotubes modifications was studied: covalent modification by surface-oxidation (MWCNT-COOH) and non-covalent modification by an addition of surfactant promoting the nanofiller-matrix interactions. A good dispersion of the MWCNT was obtained for masterbatch dilution and suspension feeding. Both methods showed preferential localization of carbon nanotubes in polycarbonate phase (PC). Samples processed by masterbatch dilution showed the 30 % increase of rigidity and a decrease of ductility of PC/ABS for 0.5 wt. % MWCNT. Electrical conductivity was influenced by processing temperature and carbon nanotubes type. The percolation threshold value was 2.0 wt. % for pristine MWCNT and 1.5 wt. % for modified MWCNT-COOH. Better balance of mechanical properties and electrical conductivity was achieved in the samples obtained by the masterbatch route. These properties were studied in a subsequent phase, when the extruded nanocomposite was injection molded in order to obtain a defined geometry.
Wegrzyn, M. (2014). Nanocomposites of Multiphase Polymer Blend Reinforced with Carbon Nanotubes: Processing and Characterization [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/36869
TESIS

The research work presented in this thesis deals with carbon nanotubes (CNTs), an allotrope of carbon with a cylindrical structure consisting of a rolled up graphene sheet. CNTs are generally produced by the decomposition of a carbon source in the presence of a metal catalyst at elevated temperatures. CNTs have outstanding properties and have attracted immense attention in both industry and academia. However, the development of commercial applications of CNTs is slow due to limitations in the large scale production of CNTs and their high cost. Another limitation is the interface resistance generated by external catalyst nanoparticles used in traditional CNT growth methods. In order to eliminate the interface resistance and simultaneously provide CNT growth over large surfaces and varying geometries, a method called direct CNT growth is established to enable the extraction of the CNT structure directly from the metal surface. The novel process for the production of CNTs developed in the present thesis is applied to planar surfaces and spherical particles made of stainless steel (SS) 304. The method is based on the establishment of nanometer scale structures at the surface which act as catalyst nanoparticles while at the same time being integral parts of the material. It uses first a mild chemical etching of the surface, followed by a specific heat treatment performed using either standard chemical vapour deposition (standard-CVD) or fluidized bed CVD (FBCVD) techniques. Acetylene (C2H2) is used as the carbon source and SS 304 acts as both the catalyst and the substrate in the growth process. This direct CNT growth with this substrate dual function eliminates the need of external catalyst nanoparticles deposited onto the surface. The active sites necessary for CNT growth are tailored on the SS itself by means of the two-step treatment process. MWNTs of 20-70 nm in diameter are produced. The CNTs are characterized by Raman Spectroscopy, Thermogravimetric analysis (TGA), Transmission Electron Microscopy (TEM) and sonication. CNT purity up to 84% is attained and the catalyst is determined to be the faced-centred cubic structure of Fe in the austenite form (γ Fe). In the case of the FBCVD technique, there are at least 30 mg of CNTs produced per total gram of sample made of CNT-coated SS particles. In addition, the recovery and reuse of the SS particles is demonstrated for a second growth sequence in the FBCVD setup. Detailed characterizations of the SS surface includes X-Ray Photoelectron Spectroscopy (XPS), grain size analysis, Atomic Force Microscopy-Kelvin Probe (AFM/Kelvin) and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). In summary, XPS reveals that the etching process partially removes the Cr2O3 passive oxide layer and results in the formation of Fe2O3. Also, Fe3C is found on the surface beneath the CNTs. This iron carbide "cementite" phase is formed during the CNT growth process. Recrystallization occurs during the heat treatment step of the method and is followed by grain growth. The AFM study confirms that the etching process creates ripple-like features on the surface, which are 10-30 nm wide. In order to stabilize mechanically and structurally the CNT growth structure on the metallic support, the production of novel Diamond-like Carbon (DLC) / CNT and Titanium Nitride (TiN) / CNT nanocomposites having a porous three-dimensional architecture is also accomplished here. The "felt-like" CNTs produced in the first part of the thesis are "frozen" in DLC or TiN by Physical Vapour Deposition (PVD). The TiN/CNT nanocomposites are characterized by nanoindentation and contact angle measurements. An increase in contact stiffness values with TiN coating time is observed. The TiN coating on the non-wetting CNTs resulted in a wetting nanocomposite surface. The wetting property was found to be a function of the TiN coating thickness on the CNT structure.
La croissance des nanotubes de carbone (NTC) sur des surfaces métalliques est étudiée dans cette thèse. En général, les NTC sont synthétisés par la décomposition d'un gaz riche en carbone en présence d'un catalyseur métallique à des températures élevées. Les propriétés exceptionnelles des NTC génèrent un immense intérêt autant au niveau de la recherche que sur le plan industriel. Par contre, le développement d'applications commerciales des NTC reste limité par les contraintes de production à grande échelle et leur prix élevé. Une autre contrainte est la résistance d'interface générée par les nanoparticules de catalyseur utilisé par les méthodes de croissance traditionnelles. Afin d'éliminer la résistance d'interface et simultanément produire une croissance des NTC sur des grandes surfaces et géométries variable, une méthode de synthèse simple et directe est développée. Cette méthode est établie pour permettre l'extraction de la structure du NTC directement à partir de la surface du métal. Le nouveau procédé de synthèse des NTC développé dans cette thèse est utilisé avec des surfaces d'acier inoxydable 304 planes et des particules sphériques. La méthode développée consiste à créer des structures nanométriques à la surface du métal qui agissent comme des particules catalytiques, tout en faisant partie intégrales de cette surface. Le procédé utilise d'abord une gravure de la surface, puis un traitement thermique réalisé soit dans un réacteur de dépôt chimique en phase vapeur traditionnel (standard-CVD), ou en lit fluidisé (FBCVD). Le gaz carboné est l'acétylène (C2H2) et le catalyseur/support combiné est l'acier inoxydable 304. Cette méthode de croissance directe des NTC avec un substrat à double fonction élimine la nécessité de déposer des nanoparticules de catalyseur sur la surface du support, les sites actifs requis pour la croissance des NTC étant produits directement sur la surface de l'acier inoxydable. La méthode optimisée produit des nanotubes multi-parois avec diamètres de 20-70 nm. Les NTC sont caractérisés par spectroscopie Raman, analyse thermogravimétrique, microscopie électronique en transmission et par une étude d'adhérence. La pureté des NTC produits atteint 84%. Des mesures de diffraction électronique sur les régions catalytiques indiquent une zone riche en fer correspondant à la structure cubique face centrée de l'austénite (γ Fe). Dans le cas du réacteur FBCVD, 30 mg de NTC sont générés pour chaque gramme de produit brut (NTC + particules d'acier inoxydable). De plus, la récupération et réutilisation des particules d'acier inoxydable pour un deuxième cycle de croissance dans le réacteur FBCVD est démontrée. La surface de l'acier inoxydable est caractérisée par plusieurs méthodes. En résumé, les analyses XPS indiquent que la couche d'oxyde de chrome (Cr2O3) est partiellement enlevé par la gravure à l'acide, et de l'oxyde de fer (Fe2O3) se forme sur la surface de l'acier inoxydable. Du carbure de fer (Fe3C) est observé sur la surface de l'acier sous les zones de croissance des NTC. Ce carbure, de la cémentite, est en fait produit durant la croissance des NTC. Le traitement thermique produit une recristallisation de la surface suivit par une croissance des grains. L'étude par AFM démontre que la gravure à l'acide génère des ondulations topographiques à une échelle de 10-30 nm sur la surface de l'acier inoxydable. Les structures de NTC sur substrat métalliques sont utilisés pour produire un nano-composite formant une structure 3-D ouverte de NTC recouverts et retenues par une couche de carbone adamantin (DLC) ou de nitrure de titane (TiN). Ces couches sont faites par dépôt physique en phase vapeur (arc-PVD). Un nombre limité d'échantillons de DLC/NTC est étudié, et une étude détaillée est effectuée pour les nano-composites TiN/NTC. Cette dernière structure est caractérisée par nano-indentation et par mesure d'angle de contact.

The focus of this study was to explore process-structure-property relationships in biodegradable polymer nanocomposite films in order to eliminate the commonly used trial and error approach to materials design and to enable manufacturing of composites with tailored properties for targeted applications. The nanofiller type and concentration, manufacturing method and compounding technique, as well as processing conditions were systematically altered in order to study the process-structure-property relationships. Polylactic acid (PLA) was used as the polymer and exfoliated graphite nanoplatelets (GNP), carbon nanotubes (CNT), and cellulose nanocrystals (CNC) were used as reinforcement. The nanocomposite films were fabricated using three different methods: 1) melt compounding and melt fiber spinning followed by compression molding, 2) solution mixing and solvent casting, and 3) solution mixing and electrospinning followed by compression molding. Furthermore, the physical properties of the polymer, namely the crystallization characteristics were altered by using two different cooling rates during compression molding. The electrical response of the composite films was examined using impedance spectroscopy and it was shown that by altering the physical properties of the insulating polymer matrix, increasing degree of crystallinity, the percolation threshold of the GNP/PLA films is significantly reduced. Additionally, design of experiments was used to examine the influence of nanofiller type (CNT versus GNP), nanofiller content, and processing conditions (cooling rate during compression molding) on the elastic modulus of the composite films and it was concluded that the cooling rate is the primary factor influencing the elastic modulus of both melt compounded CNT/PLA and GNP/PLA films. Furthermore, the effect of nanofiller geometry and compounding method was examined and it was shown that the high nanofiller aspect ratio in the CNT/PLA films led to decreased percolation threshold compared to the GNP/PLA films. The melt compounded GNP/PLA films displayed a lower percolation threshold than the solution cast GNP/PLA films most likely due to the more homogeneous distribution and dispersion of GNP in the solution cast films. Fully biodegradable and biorenewable nanocomposite films were fabricated and examined through the incorporation of CNC in PLA. Through the addition of CNC, the degree of crystallinity of the matrix was significantly increased. Focusing the design space through investigation of process-structure-property relationships in PLA nanocomposites, can help facilitate nanocomposites with tailored properties for targeted applications.

PVDF, Poly(vinylidene fluoride), is a polymer that has been studied for over four decades due to its good electromechanical properties, stability, and durability in various environments. Currently, PVDF is the only commercially available piezoelectric polymer. PVDF is a polymorph, which indicates the presence of several crystalline phases such as α, β, γ, and δ-phase. Oriented β-phase PVDF exhibits ferroelectric properties and displays the largest piezoelectricity amongst the four phases, which makes it the most desirable phase. Preparing oriented β-phase PVDF is a multi-step process, which is cost intensive, due to the time, labor and energy utilized. The main goal of this work is to prepare oriented β-phase PVDF using the electrospraying technique in a one step process. During the electrospraying process a polymer jet is ejected. This jet disintegrates into droplets due to overwhelming surface tension, resulting in a sprayed coating on the collector substrate. Because of the combination of jet ejection and the high voltage applied between the needle tip and the substrate, the droplets can be stretched and the polymer chains can be oriented. Both the stretching and the high electric field are required for the transformation of α-phase to the oriented β-phase. This study proposes that by using the electrospraying technique it is possible to transform the α-phase to the β-phase in a one step process starting from solution. This research focuses on the processing and characterization of electrosprayed PVDF as well as electrosprayed PVDF/carbon nanotubes (PVDF/CNT) nanocomposites. The specific tasks are to determine the changes to the PVDF phases due to the electrospraying technique, and to determine the changes in the PVDF morphology due to the addition of carbon nanotubes to the polymer matrix.PVDF with two different molecular weights were electrosprayed using different solvents and parameters. Initial observations after electrospraying were that, high boiling point solvents resulted in the spraying of the solution and forming films, whereas a low boiling point volatile solvent such as acetone resulted in the spinning of the solution thus forming non-woven fiber mats. The thermal and electrical properties of the electrosprayed PVDF and PVDF/CNT composites are measured using several characterization techniques, including Modulated Differential Scanning Calorimetry (MDSC), Dielectric spectroscopy, Thermally Stimulated Current (TSC), Fourier Transform Infrared Spectroscopy (FT-IR), and X-Ray Diffraction (XRD). MDSC results show that electrosprayed PVDF has a lower melting point temperature than that of PVDF commercially available pellets. In addition, electrosprayed PVDF/CNT nanocomposites show a linear increase in the percentage of crystallinity with the increase of CNT concentration in the composite. Dielectric spectroscopy results indicate that by increasing the CNT concentration in the composite, the dielectric constant and the polymer conductivity increase.From the four characterizing techniques used, two of them, FT-IR and XRD, show that it is possible to transform α-phase to β-phase PVDF in a one-step process using electrospraying. The other two techniques, TSC and dielectric spectroscopy, show α-phase for the electrosprayed samples without CNT, and some β-phase formation with samples electrosprayed with CNT. These last two techniques; TSC and dielectric spectroscopy have results that differ from the FT-IR and XRD techniques. This contradiction may be a result of the small amounts of β-phase in the sample, which cannot be detected using these techniques. Another reason may be due to the difference in the probing levels between these techniques. XRD and FT-IR probe at the molecular level, whereas TSC and dielectric probe at a much larger scale, which may make it hard to detect small amounts of β-phase.

Thesis (M. S.)--Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Kumar, Satish; Committee Member: Bucknall, David; Committee Member: Griffin, Anselm; Committee Member: Shofner, Meisha; Committee Member: Yushin, Gleb

Cette thèse traite de la modification de surface des nanotubes de carbone avec des polymères Le chapitre I présente l'état de l'art des matériaux hybrides associant des liquides ioniques avec des nanotubes de carbone (NTC) ou du graphenes. Le chapitre II commence par un aperçu général de l'adsorption non-covalente de polymères sur la surface de NTC, suivi d'une description détaillée de l'étude réalisée sur la fonctionnalisation non covalente des nanotubes de carbone avec divers liquides ioniques polymérisable (LIP) à base d'imidazolium. Dans ce cadre, nous avons comparé deux méthodes expérimentales: la polymérisation in situ et le mélange en solution. Une des applications les plus importantes des NTC se situe dans le domaine des nanocomposites polymères/NTC. Le chapitre III décrit la formation de composites polyetherimide/NTC à partir des NTC-LIP obtenue dans la chapitre II. La préparation des composites en utilisant la méthode dite « solvent casting » est détaillée. Les NTC bruts, oxydés à l'acide nitrique et fonctionnalisé par le LIP ont été comparés. Des mesures mécaniques, thermiques et électriques de ces composées ont été aussi réalisées. Le dernier chapitre, divisé en deux sections, traite de la fonctionnalisation covalente des nanotubes de carbone avec une variété de polymères en utilisant deux approches différentes: "grafting from" et "grafting to". En utilisant la première approche, nous avons réalisé la croissance de chaînes de polyamide (PA) à partir de la surface de nanotubes de carbone fonctionnalisés avec le caprolactame par polymérisation anionique par ouverture de cycle. Les propriétés de traction des composites à base de PA ainsi préparées ont été étudiées. La polymérisation radicalaire de monomères vinyliques à base de LI de type imidazolium greffés à la surface de NTC est également présentée dans cette partie. Dans la deuxième partie du chapitre IV, nous présentons plusieurs stratégies de fonctionnalisation, y compris l'addition radicalaire et le greffage sur les défauts de NTC, pour la préparation des NTC fonctionnalisés de manière covalente avec des polymères compatibles avec des matrices époxy
This thesis deals with the surface modification of multi-walled carbon nanotubes with polymers with the aim to achieve a high level of dispersion in polymer matrices. Chapter I gives a comprehensive review of the state of the art of hybrids of ionic liquids with carbon nanomaterials, particularly, nanotubes and more recently, graphene. Chapter II starts with a general overview of the non-covalent adsorption of polymers onto the CNT surfaces followed by a detailed description of the study carried out on the non-covalent functionalization of CNTs with various imidazolium based polymerized ionic liquids (PIL). For this purpose, we further compare the two experimental methods: in situ polymerization and solution mixing. One of the most important applications of CNT is in polymer/CNT composites. Chapter III describes the formation of polyetherimide/CNT composites starting from PIL-CNT hybrids obtained in Chapter II. The preparation and characterization of composites using solvent casting methods have been detailed. Pristine, acid oxidized and PIL functionalized CNTs have been compared. Mechanical, thermal and electrical property measurements on these composites have also been described. The last chapter – Chapter IV, divided into two sections, discusses the covalent functionalization of CNTs with a variety of polymers using two main approaches: “grafting from” and “grafting to”. Using the first approach we have grown polyamide (PA) chains from the surface of caprolactam grafted CNTs by anionic ring opening polymerization. The tensile properties of the PA based composites prepared therefrom containing pristine, amine- and PA-functionalized CNTs have been investigated. The radical polymerization of vinyl imidazolium based IL monomers attached to the activated CNT surface is also given in this section. In the second part of Chapter IV, we have reported several “grafting to” functionalization strategies including radical addition and “defect site” grafting used for the preparation of CNTs covalently attached with polymers intended to blend well with epoxy matrices

L’utilisation de composites à matrice thermodurcissable et fibres continues est en constante progression dans le secteur aéronautique, ferroviaire, et automobile. Afin d’améliorer les composites obtenus, notamment leur résistance à l’impact et leur conductivité électrique, des nanocharges organiques ou inorganiques peuvent être ajoutées. Les nanotubes de carbone (CNT) font partie des candidats les plus prometteurs pour le renforcement de composites à multi-échelle. Cependant, il s’avère difficile de contrôler la dispersion, la répartition et l’orientation des CNT, après les avoir mélangés aux prépolymères. Une nouvelle stratégie d’insertion des CNT dans un composite consiste à combiner des fibres de CNT avec des fibres de carbone. L’orientation et l’organisation structurelle des CNT au sein de la fibre permettent d’obtenir d’excellentes propriétés mécaniques et électriques. Dans notre étude, les propriétés de fibres contenant exclusivement des CNT, obtenues par direct spinning, ont été comparées à celles de fibres de carbone (non-ensimées, ensimées, et CNT en surface). Différentes interfaces entre les fibres de CNT, fibres de carbone et deux types de matrices époxy (de TG très différentes) ont été générées et testées par des essais de fragmentation de fibre dans la matrice. La contrainte de cisaillement interfaciale fibre/matrice a été évaluée afin de déterminer l’influence des diverses fibres et ensimages sur les performances mécaniques de composites à matrice organique et à fibres continues. En outre, la nature de l’adhésion et la qualité de l’interphase entre la matrice et la fibre ont été caractérisées par plusieurs techniques d’analyses et d’observations à multi-échelles
Nowadays, polymer-matrix composites reinforced with carbon fibers are increasingly used in the whole transport sector (aerospace, automotive and railway industries). However, the obtained parts still suffer from low impact resistance and low damage tolerance. To improve these properties, the matrix precursors have to be combined with organic or inorganic compounds to lead to multi-phased matrices. Among them, carbon nanotubes (CNT) are especially promising for targeting multi-scale reinforcement. Since high quality of the parts are required, continuous-fibers-reinforced composites can be produced by resin transfer molding (RTM) which also offers a reduced cost if compared with high temperature- and high pressure-based processes. However, RTM requires a very low viscosity of the polymer precursors and CNT-filled precursors are far too viscous to be injected on dry performs. In addition, this strategy does not allow for a control of the CNT location and orientation in the final part. In this study, innovative ways have been developed to insert CNT in the preform with local positioning and defined orientation. Deliveries of CNT in the matrix, from a neat carbon multi-nanotubes fiber produced by direct spinning, or from a CNT grown on carbon fiber were investigated in two types of epoxy matrices (with very different TG). Different polymer matrix/fiber interfaces have been generated using neat carbon multi-nanotubes fiber, CNT grown on carbon fiber and conventional carbon fiber, with or without sizing. A fine mechanical characterization of various fibers and particularly the measurement of single fiber interfacial properties have been performed in order to determine mechanical performance of continuous fiber reinforced composites. In addition, the nature of adhesion and quality of matrix/fiber interface have been fully evaluated by different multi-scale analyses and suitable microstructural observations

Orientador: Prof. Dr. Daniel Zanetti de Florio
Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, 2015.
O trabalho realizado mostra a influência do aumento da concentração de nanotubos de carbono sobre a propriedade de impedância, em um nanocompósito a base de policarbonato e nanotubos de paredes múltiplas. Neste trabalho, o polímero policarbonato (PC) foi misturado em diversas concentrações com nanotubos de carbono de paredes múltiplas (MWCNT) do tipo "não purificado" formando nanocompósitos. As amostras foram preparadas por dissolução do PC em clorofórmio, seguido pela adição de MWCNT e surfactante. As misturas foram dispersas em banho de ultrassom, o solvente foi extraído por evaporação, as amostras foram moídas, desumidificadas, extrudadas em plastômetro e preparadas para a caracterização. Foi realizada análise por meio de microscópia eletrônica de varredura, ensaios de tração e termogravimetria. Uma amostra foi exposta ao contato com álcool para verificar a possível sensibilidade a esta substância. Foi realizada medição da condutividade e da espectroscopia de impedância na faixa de frequência entre 1 MHz a 1 Hz, variando-se as tensões alternadas entre 10 mV e 500 mV. Entre os principais resultados observaram-se dois comportamentos possíveis que modelam os resultados de impedância. Em menores concentrações de MWCNT, as amostras podem ser representadas por um circuito composto por dois resistores (R1, R2) e um capacitor (CP), sendo que o conjunto R2 e CP (ligados entre si em paralelo) está ligado em série com R1. Para amostras com maiores concentrações de MWCNT, o circuito equivalente pode ser representado por apenas um resistor simples. Observa-se que com o incremento da concentração de MWCNT a resistência elétrica dos nanocompósitos é reduzida. Uma das amostras, após ser exposta ao etanol, apresentou um aumento no valor da impedância elétrica, o que se caracteriza como uma "resposta" elétrica à exposição química.
The work shows the influence of the concentration of carbon nanotubes on the impedance property in a nanocomposite based polycarbonate and multi-walled nanotubes. In this work, polycarbonate polymer (PC) was mixed at various concentrations with multi-walled carbon nanotubes (MWCNT) type "as grown" forming a nanocomposite. The samples were prepared by dissolving the PC in chloroform, followed by addition of MWCNT and surfactant. The mixtures were dispersed in an ultrasound bath, the solvent was removed by evaporation, the samples were ground, dried, extruded in plastometer and prepared for characterization. Analysis was performed using scanning electron microscopy, tensile and thermogravimetry tests. A sample was exposed to contact with alcohol to verify the possible sensitivity to this substance. Conductivity and Impedance spectroscopy measurements were conducted in the frequency range from 1 MHz to 1 Hz by varying alternating voltages between 10 mV and 500 mV. The main results were observed two possible behaviors that model the impedance results. At lower concentrations of MWCNT samples may be represented by a circuit composed of two resistors (R1, R2) and a capacitor (CP). The group R2 and CP, connected in parallel, is connected in series with R1. For samples with higher concentrations of MWCNT the equivalent circuit can be represented by just a single resistor. It is observed that with increasing concentration MWCNT the electrical resistance of the nanocomposite is reduced. One of the samples after being exposed to ethanol, showed an increase in the value of electrical impedance, which is characterized as an electrical "response" to the chemical exposure.

Les composites renforcés avec des nanotubes de carbone présentent un réel potentiel en terme de renforcement mécanique, d’amélioration de conductivités électrique et thermique des matériaux cependant les effets toxicologiques des nanotubes de carbone sur la santé humaine sont toujours à l’étude, et tout laisse à penser que ceux-ci feront prochainement l’objet de normes et autres législation. C’est pourquoi les fabricants de composites renforcés nanotubes de carbone ont tout intérêt à prendre les devants sur de futures législations en contrôlant le relargage de nanotubes isolés lors de différentes sollicitations de ces matériaux telles que la casse ou l’abrasion. Un bon état de dispersion des nanotubes au sein de la matrice est un paramètre qui améliore les performances du composite et que l’on suppose faire baisser le relargage de nanotubes de carbone isolé dans l’environnement. Le but final de cette étude est donc ici de savoir si la qualité de l’état de dispersion des nanotubes influe sur la nature des particules relarguées suite à une dégradation d’un composites. Il faut savoir si l’on a relargué des nanotubes isolés, ou bien des particules de polymère dans lesquelles des nanotubes seraient complètement enrobés, d’où l’intérêt de bien maitriser cette étape de dispersion. Pour contrôler la dispersion des nanotubes de carbone dans un système polymère, différentes méthode peuvent être utilisées, notamment la microscopie électronique (MEB et MET), mais également des méthodes telles que la caractérisation des propriétés mécaniques, la conductivité électrique, thermique ou encore la rhéologie des suspensions. Ces différentes méthodes étant plus ou moins efficaces et simple à mettre en œuvre pour indiquer si les nanotubes sont individuellement dispersés, en fagots, voire en agglomérats. Une fois l’état de dispersion des composites biens caractérisés, il s’agit de le corréler avec une prédisposition plus ou moins prononcée de ce nanocomposite au relargage. La théorie prédit que l’interface entre un nanotube et le polymère est supposé bien plus forte que celle entre un nanotube entouré par d’autres nanotubes au sein d’un agrégat. Des observations microscopiques de fractures ainsi que la caractérisation des particules relarguées lors des tests en abrasion standardisés (mesures granulométriques combinées à des observations par microscopie électronique) menées sur ces matériaux modèles permettent alors de confirmer les prédictions théoriques et de caractériser les particules relarguées en termes de taille, nombre et nature. Les résultats ne permettent pas d’affirmer que des nanotubes de carbone isolés sont relargués pendant la sollicitation mécanique des nanocomposites, quel que soit l’état de dispersion des nanotubes de carbone. En revanche, les interactions entre les particules de matrice polymère et les nanotubes de carbone observés sur celles-ci, apparaissent extrêmement dépendantes de cet état de dispersion
Carbon nanotubes (CNT) reinforced polymer-based composites represent a significant opportunity in terms of mechanical reinforcement and electrical and thermal conductivity improvements. However specific issues for nanotubes and related composites on human health are still under studied. It is strongly expected that standards and regulations on carbon nanotubes and on carbon nanotubes composites should appear soon. Due to their high aspect ratio they could migrate into breathing apparatus (because of their small diameter) and remain stuck to the walls (due to their length) causing damages like pulmonary fibrosis or cancer. Exposition of human people to carbon nanotubes must be controlled and an occupational exposure limit must be defined. That is why suppliers of carbon nanotubes have large interest to predict rules in controlling carbon nanotube release during the use of materials prepared from nanotubes, especially under abrasion or other cyclic mechanical solicitations. A key point is to check if a good dispersion state is a required condition to decrease isolated carbon nanotubes release. As the dispersion state of carbon nanotubes in polymer-based nanocomposites was known and controlled, standardized abrasion tests were performed in a glove box in order to simulate the wear use of a nanocomposite during its lifecycle, i.e. to generate particles. Released particles were collected on TEM grids and by particle sizing devices and these ones were analyzed in term of number, size and nature thanks to different characterization methods. Granulometric data, TEM micrographs and EDX measurements were all performed and founded to be influenced by several parameters amongst which the carbon nanotubes dispersion state. Carbon nanotubes were found in the abraded particles but never isolated from other polymer particles but could be linked to released polymer particles via Van der Waals interactions and physical entanglement. It clearly appears that the dispersion state of CNT has an influence on the shape and the aspect of released particles

Ce travail de thèse porte sur les relations entre les paramètres de mise en œuvre à l’état fondu et les propriétés d’un composite hybride à matrice thermoplastique. Les charges étudiées sont les fibres de verre courtes (échelle micrométrique) et les nanotubes de carbone (NTC) (échelle nanométrique) dispersées dans une matrice thermoplastique thermostable, le poly(éther imide) (PEI). Nous avons montré que les fibres de verre participent fortement à la structuration du réseau de NTC et que la conductivité électrique du composite hybride est plus élevée que celle des nanocomposites. Les paramètres de mise en œuvre et notamment le paramètre Energie Mécanique Spécifique (EMS) a une forte influence sur les propriétés des composites hybrides et notamment sur la conductivité électrique. Il a été montré que les variations de conductivité électrique sont la conséquence d’un changement d’état de dispersion des NTC. Le taux de fibres de verre introduit dans le nanocomposite PEI/NTC a une forte influence sur la conductivité du composite hybride. Il est possible de contrôler la conductivité électrique du composite multi-échelles en modifiant le taux de fibres de verre introduit notamment pour des concentrations en NTC proche du seuil de percolation
This PhD work deals with the relationship between the processing parameters at the melt state and the polymer matrix hybrid composite material’s properties. The fillers studied are short glass fibres (micrometric scale) and carbon nanotubes (CNT) (nanometric scale) dispersed in a high temperature polymer matrix, the poly(etherimide) (PEI). We showed that glass fibres strongly participate in the CNT network structuration and that electrical conductivity of multiscale composite materials is higher than the one of nanocomposite materials. The combination of the two fillers allows obtaining a synergy effect for the mechanical properties especially for the elongation at break which is due to a preferential localization of CNT at the PEI/glass fibres interfaces. The study of the influence of processing parameters on the properties of nanocomposite materials and hybrid composite materials showed that Specific Mechanical Energy (SME) has a strong influence on the hybrid composite material properties and especially on the electrical conductivity. These variations are the consequences of CNT network modifications. Glass fibres concentration has also a strong influence on the electrical conductivity of the hybrid composite materials. It is possible to adjust the electrical conductivity with modifying the concentration of glass fibres especially for the CNT amount closed to the electrical percolation threshold

La thèse concerne les synthèse et caractérisation de composites polymères nanostructurés à base d’esters de cyanates de bisphénol a (DCBA) ou à base d’oligomères cycliques de butylène téréphtalate (CBT) et de nanotubes de carbone multi-parois (MWCNTS). L’effet catalytique des nanotubes de carbone sur la polycyclotrimerisation de DCBA et aussi sur la polymérisation du CBT est observé. L’augmentation de la température de cristallisation a été fixée pour tous les échantillons de nanocomposites à base de polybutylène téréphtalate (cPBT). L’effet de la méthode de mise en forme de cPBT/MWCNTS sur ses propriétés thermiques et électriques a été établi. Il est observé que le traitement thermique additionnel des échantillons (recuit) à des températures inférieures à celle de la fusion du cPBT cause la réagglomération des MWCNTS dans le système. Il est établi que l’ajout de très bas taux de MWCNTS (0.03-0.06 pour cent en masse) dans la matrice de polycyanurate (PCN) augmente les valeurs de résistance à la flexion (64-94 pour cent). De même l’ajout de 0.01 pourcent de MWCNTS en masse dans le CBT augmente considérablement le module d'élasticité des nanocomposites cPBT. Cet effet a été expliqué par la dispersion efficace de cette faible quantité de nanocharges pendant la synthèse in situ de la matrice de cPBT et est confirmée par les clichés en microscopie. Il est déterminé que les propriétés électriques des nanocomposites à base d’esters hétérocycliques et MWCNTS peuvent varier de matériaux isolants aux matériaux conducteurs. Les seuils de percolation des deux systèmes sont très bas (0.22 et 0.38 pourcent pour nanocomposites à base de cPBT et PCN respectivement). La conductivité des composites conducteurs est particulièrement stable sur un large domaine de température ce qui laisse présager des applications intéressantes dans le domaine de la microélectronique et pour des pièces d’avion et de navettes spatiales
The thesis relates to synthesis and investigation of nanostructured polymer composites based on oligomers of cyanate esters of bisphenol a (DCBA) or cyclic butylene terephthalate (CBT) and multiwalled carbon nanotubes (MWCNTS). Catalytic effect of mwcnts in process of DCBA polycyclotrimerization as well as in cbt polymerization has been observed. Significant increase in crystallization temperature of nanocomposites based on polybutylene terephthalate (cPBT) with adding of MWCNTS is observed. The effect of processing method of cpbt/mwcnts nanocomposites on its electrical properties has been found. It has been established that the additional heating of the samples (annealing) at temperatures above melting of cPBT leads to reagglomeration of MWCNTS in the system. It is established that reagglomeration of MWCNTS results in increase of conductivity values of nanocomposites due to formation of percolation pathways of MWCNTS through polymer matrix. In the case of polycyanurate matrix (PCN), it is found that addition of small mwcnts contents (0.03-0.06 weight percents) provides increasing tensile strength by 62-94 percents. It has been found that addition of even 0.01 weight percents of MWCNTS provides significant increase in storage modulus of cPBT matrix. This is explained by effective dispersing of small amount of the nanofiller during in situ synthesis of pcn or cpbt matrix that is confirmed by microscopy techniques. It has been established that the properties of the nanocomposites based on heterocyclic esters and MWCNTS can be varied from isolator to conductor and has low percolation thresholds (0.22 and 0.38 weight percents for cPBT and PCN nanocomposites respectively). The conductivity of samples is particularly stable on a very large range of temperature from 300 to 10 degrees Kelvin that make these materials perspective for practical applications in microelectronics, as parts of aircraft and space constructions

The thesis relates to synthesis and investigation of nanostructured polymer composites based on oligomers of cyanate esters of bisphenol a (DCBA) or cyclic butylene terephthalate (CBT) and multiwalled carbon nanotubes (MWCNTS). Catalytic effect of mwcnts in process of DCBA polycyclotrimerization as well as in cbt polymerization has been observed. Significant increase in crystallization temperature of nanocomposites based on polybutylene terephthalate (cPBT) with adding of MWCNTS is observed. The effect of processing method of cpbt/mwcnts nanocomposites on its electrical properties has been found. It has been established that the additional heating of the samples (annealing) at temperatures above melting of cPBT leads to reagglomeration of MWCNTS in the system. It is established that reagglomeration of MWCNTS results in increase of conductivity values of nanocomposites due to formation of percolation pathways of MWCNTS through polymer matrix. In the case of polycyanurate matrix (PCN), it is found that addition of small mwcnts contents (0.03-0.06 weight percents) provides increasing tensile strength by 62-94 percents. It has been found that addition of even 0.01 weight percents of MWCNTS provides significant increase in storage modulus of cPBT matrix. This is explained by effective dispersing of small amount of the nanofiller during in situ synthesis of pcn or cpbt matrix that is confirmed by microscopy techniques. It has been established that the properties of the nanocomposites based on heterocyclic esters and MWCNTS can be varied from isolator to conductor and has low percolation thresholds (0.22 and 0.38 weight percents for cPBT and PCN nanocomposites respectively). The conductivity of samples is particularly stable on a very large range of temperature from 300 to 10 degrees Kelvin that make these materials perspective for practical applications in microelectronics, as parts of aircraft and space constructions.

Des films à base de nanotubes de carbone et d'oxyde de graphène reduit ont été préparés sur des électrodes d'or de microbalances et testées dans différents électrolytes tels que LiCl, NaCl et KCI. Le stockage de charge au sein de ces films a été étudié par ac-électrogravimétrie, couplage entre une microbalance à quartz rapide (QCM) et la spectroscopie d'impédance électrochimique (EIS). La nature chimique et le rôle de chaque espèce, anion, cation, cation solvaté, solvant libre, impliquée dans le mécanisme de stockage de charge, ont été clairement identifiés au cours de la polarisation cathodique et anodique par ces mesures d'ac-électrogravimétrie pour la première fois. Les résultats d'ac-électrogravimétrie confirment que les cations sont en majorité électroadsorbés lorsque la surface est chargée négativement, tandis que les anions sont électroadsorbés lorsque la surface est chargée positivement. Des films nanocomposites, SWCNT/Bleu de Prusse et de SWCNT/Polypyrrole ont aussi été électrochimiquement examinés. La nature chimique et le rôle de chaque espèce impliqués dans les processus faradiques et capacitifs ont été mis en évidence par ac-électrogravimétrie. La méthodologie adaptée pour caractériser des électrodes à base de carbone peut être proposé comme un outil de diagnostic de référence pour étudier la relation pore/taille des ions, la concentration et les effets de solvant, la dynamique des interactions des ions au niveau des interfaces (électroadsorption et/ou processus faradique). Cela peut permettre d'obtenir des matériaux d'électrode ouvrent la voie vers des systèmes électrode/électrolyte plus performants dans les dispositifs de stockage d'énergie
Carbon nanotubes (CNTs) and Electrochemically Reduced Graphene Oxide films were prepared on gold electrodes of microbalance and tested in different electrolytes such as LiCl, NaCl and KCl. The capacitive charge storage of carbon-based film electrodes were investigated by ac-electrogravimetry which couples fast quartz crystal microbalance (QCM) and electrochemical impedance spectroscopy (EIS). The chemical nature and the role of each species, anion, cation, solvated cation, free solvent, involved in the charge storage mechanism, have been clearly identified during the cathodic and anodic polarization through ac-electrogravimetry measurements for the very first time. The ac-electrogravimetric results confirm that the cations are predominantly electroadsorbed when the surface is negatively charged while the anions are electroadsorbed when the surface is positively charged. Nanocomposite films, namely SWCNT/Prussian Blue and SWCNT/Polypyrrole were electrochemically examined. The main idea was to emphasize the capacitive and faradic behavior of these different films by combining two materials. The chemical nature and the role of each species involved in the pseudo-capacitive and capacitive processes were highlighted by the ac-electrogravimetry. The methodology adapted to characterize carbon based electrodes can be suggested as a baseline diagnostic tool to study the pore/ion size relationship, the concentration and the solvent effects, the dynamics of the ions interactions at the interfaces (electroadsorption and/or faradaic process) of the electrode materials which may pave the way towards more performant electrode/electrolyte systems in energy storage devices

L'objectif de cette thèse est l'identification de couplages (nanoparticules / matrice de poly(methyl-methacrylate) PMMA) qui renforcent la rigidité de surface du PMMA tout en conservant le maximum de transparence. Le choix s'est porté sur trois type de nanoparticules carbonées : du graphène multicouches (FLG), de l'oxyde de graphène (GO) et des nanotubes de carbones (MWCNT). Une première décrit la préparation et la fonctionnalisation de ces trois types de nanoparticules pour assurer une meilleure dispersion dans la matrice. Deux méthodes ont été retenues pour réaliser ces matériaux composites : la polymérisation en masse et le mélange en solution. Une seconde partie présente la caractérisation des propriétés mécaniques de ces revêtements en trois étapes : en volume, en surface et sous forme de revêtement en couches minces (15-20µm). Les résultats majeurs montrent que les nano-composites réalisés retardent l'apparition de la plasticité comparé à un PMMA pur, même à faible pourcentage, et permettent ainsi de limiter les effets de rayures de surfaces. Le faible pourcentage de renfort permet de conserver la transparence et plus l'épaisseur diminue plus on peut augmenter ce taux de renfort sans dégrader les propriétés mécaniques du revêtement. Les nanoparticules choisies comme agents de renfort de la matrice polymère s'avèrent être également de très bons candidats pour la diminution du frottement comparée à un plastifiant type Erucamide
The goal of this thesis is the identification of couplings (nanoparticles / matrix poly (methyl methacrylate) PMMA) which ensure PMMA surface rigidity while maintaining maximum transparency. The choice fell on three types of carbonaceous nanoparticles: Few layer graphene (FLG), graphene oxide (GO) and carbon nanotubes (MWCNT). A first part describes the preparation and functionalization of these three types of nanoparticles to provide a better dispersion in the matrix. Two methods were used to prepare nanocomposite materials: bulk polymerization and solution blending. A second part presents the characterization of the mechanical properties of these coatings in three stages: volume, surface and thin layer coating (15-20μm). The main results show that nanocomposites made delay the onset of plasticity compared with pure PMMA, even at a low percentage, and help to limit the effects of surface scratches. The small percentage of reinforcement keeps the transparency and the more the thickness decreases the more the rate of reinforcement can increase without degrading the mechanical properties of the coating. Moreover, nanoparticles chosen as the polymer matrix of reinforcing agents prove to be very good candidates for reduction in friction compared to a plasticizer such Erucamide

In this study, we propose a multi-walled carbon nanotube epoxy composite sensor for force and pressure sensing in the range of 50 N–2 kN. A manufacturing procedure, including material preparation and deposition techniques, is proposed. The electrode dimensions and the layer thickness were optimized by the finite element method. Temperature compensation is realized by four nanocomposites elements, where only two elements are exposed to the measurand. In order to investigate the influence of the filler contents, samples with different compositions were prepared and investigated. Additionally, the specimens are characterized by cyclical and stepped force/pressure loads or at defined temperatures. The results show that the choice of the filler content should meet a compromise between sensitivity, temperature influence and noise behavior. At constant temperature, a force of at least 50N can be resolved. The measurement error due to the temperature influence is 150N in a temperature range of –20°C–50°C.

The use of graphene and conductive polyaniline nanomaterials in the field of electrochemistry is increasing due to their excellent conductivity, rapid electron transfer and high specific surface area. However, these properties are strongly dependent on the preparation processes. To accelerate the development of advanced electrochemical sensors for the simultaneous detection of trace amounts of heavy metal ions, two facile and green methods are proposed to improve their performance in this thesis. The first one was dedicated to make graphene-carbon nanotube hybrid nanocomposites. The introduction of carbon nanotubes not only greatly enhances the conductivity of graphene but also suppresses, to some degree, the aggregation between graphene nanosheets. Another method proposed in this thesis work was to synthesize a phytic acid doped polyaniline nanofiber based nanocomposite. The synergistic contribution from polyaniline nanofibers and phytic acid enhances the accumulation efficiency and the charge transfer rate of metal ions during the differential pulse anodic stripping voltammetry analysis. The above-mentioned nanocomposite modified electrodes were all successfully applied to real samples for the simultaneous detection of Cd2+ and Pb2+ with good recovery rates. Meanwhile, corrosion protection is another important branch in the field of electrochemistry. In this direction, an active alkyd-polyaniline composite coating with self-healing functionality was prepared. The polyaniline used in this thesis was doped with p-toluene sulfonic acid, which was employed to increase the conductivity of polyaniline, and 1 wt.% of as-prepared polyaniline nanoparticles were found to offer an effective conductive network for anticorrosion. Finally, the reasons that such low loading levels of nanomaterials can result in significantly reinforced properties in nanocomposites were studied with combined atomic force microscopy (AFM) techniques. The results demonstrated that the interphase for a 40-nm-sized silica particle could extend to 55–70 nm in poly(ethyl methacrylate) (PEMA) and poly(isobutyl methacrylate) (PiBMA) polymer matrix, and the interphase exhibited a gradient distribution in surface nanomechanical properties.

QC 20170315

Los nanomateriales, especialmente las nanopartículas, se convierten en una de las áreas más atractivas no sólo en la investigación científica, sino también en las aplicaciones industriales. En esta tesis se ha estudiado la preparación de nanopartículas de magnetita, sus nanocompuestos relacionados y la aplicación de los nanomateriales obtenidos. Las nanopartículas core-shell de Fe3O4@SiO2 se sintetizaron mediante métodos de microemulsión inversa estándar y de microondas. Las nanopartículas obtenidas se caracterizaron con diferentes técnicas de laboratorio y se estudiaron los diferentes efectos al cambiar algunos parámetros (temperatura, concentración, tiempo) de la reacción. Las nanopartículas se utilizaron como soporte de catalizadores de Ag y los nanocompuestos sintetizados mostraron una buena propiedad catalítica y una alta capacidad de reciclaje. También se prepararon nuevas nanocápsulas de Fe3O4@GNF@SiO2 mediante la formación in situ de nanopartículas de magnetita y el proceso de cobertura de sílica. Los nanocapsulados obtenidos tienen una buena estabilidad incluso en ambientes ácidos. También se estudió la posible aplicación de estas nanocápsulas por resonancia magnética. Por otra parte, se estudió la citotoxidad e interacción del core-shell Fe3O4 @ SiO2 de las nanopartículas unidas a células, para asegurarse una posible aplicación en investigación biomédica obteniendo un resultado favorable y de baja toxicidad. A continuación, las nanopartículas Fe3O4 @ SiO2 se decoraron añadiendo biomoléculas tales como MC540 y L-tiroxina las cuales muestran una posible aplicación en el estudio de biosensores.
Nanomaterials especially nanoparticles become one of the most attractive area not only in scientific research but also in industrial applications. In this thesis, the preparation of magnetite nanoparticles, their related nanocomposites and the application of those obtained nanomaterials have been studied. The Fe3O4@SiO2 core-shell nanoparticles were synthesized via normal and microwave assistance reverse microemulsion methods. The obtained nanoparticles were fully characterized with different laboratory techniques and the effect of reaction parameters on final products was also studied. These nanoparticles were used as a support of Ag catalysts nanoparticles and the as synthesized nanocomposites shown nice catalytic property and high recyclability. A novel Fe3O4@GNF@SiO2 nanocapsulates were also prepared via in situ formation of magnetite nanoparticles and silica coverage process. The obtained nanocapsulates have nice stabilities even in the acid environments. The potential application of these nanocapsulates in magnetic resonance imaging research was also studied. On the other hand, the cytotoxity and interaction with cell of Fe3O4@SiO2 core-shell nanoparticles were studied which indicate the possibility of using them in biomedical research. Then, the Fe3O4@SiO2 core-shell nanoparticles were further decorated with biomolecules such as MC540 and L-thyroxine. The Fe3O4@SiO2 core-shell nanoparticles with the surface functionalized with molecule imprinted polymers also suggested the potential application in biosensor research.

The current state of wireless sensing technologies possesses a good reliability in terms of time response and sensing on movable parts or in embedded structures. Nevertheless, these tech- nologies involve energy supply such as battery and suffer from low resolution and bulky signal conditioning system for data processing. Thus, a RFID passive wireless sensor is a good candidate to overcome these issues. The feasibility of implementing microstrip patch antennas for sensing application were successfully investigated; however, low sensitivity was always a big issue to be concerned. Sensors based on nanocomposites attracted a lot of attention because of their excellent performance in term of light weight, high sensitivity, good stability and high resistance to corrosion but it lacks the capability of high conductivity, which limit their implication into RFID applications. This work introduces a novel high sensitive passive wireless strain and temperature sensors based on nanocomposites as sensing layer. To accomplish this, intrinsically conductive polymer based on carbon nanofillers nanocomposites are deeply studied and characterized. Then it’s performance is evaluated. Among them a novel tertiary nanocomposite is introduced, which opens the gate to new nanocomposite applications and thus broad- ens the application spectrum. Understanding the transport mechanism to improve the conductivity of the nanocomposite and extracting individually different models based on physical explanation of their piezoresistivity, and behavior under temperature and humidity have been developed. Afterwards, selected nanocomposites based on their high sensitivity to either strain or temperature are chosen to be used as sensing layer for patch antenna. The fabricated patch antenna has only one fundamental frequency, by determining the shift in its resonance frequency as function of the desired property to be measured; the wireless sensor characteristics are then examined. For strain sensing, the effect of strain is tested experimentally with the help of end-loaded beam measurement setup. For temperature sensing, the sensors are loaded in a controlled temperature/humid chamber and with the help of a vector network analyzer, the sensitivity of the antennas are extracted by acquiring the shift in the resonance frequency. The fabricated wireless sensors based on patch antenna are fabricated on very low lossy material to improve their gain and radiation pattern. This approach could be expanded also to include different type of substrates such as stretchable substrates i.e. elastomer polymer, very thing substrates such as Kapton, paper-based substrates or liquid crystal polymer.

Orientador: Nelson Eduardo Duran Caballero
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química
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Resumo: Esse trabalho avaliou o efeito da adição de nanotubos de carbono de paredes múltiplas (NTC) nas propriedades térmicas e mecânica, morfologia e hidrofobicidade do poli(3-hidroxibutirato-co-3-hidroxivalerato), o PHBV. A adição de nanotubos de carbono poderia implicar em melhora das propriedades do PHBV, um poliéster natural que devido à sua biodegradabilidade e biocompatibilidade possui um grande potencial de aplicação. Assim, nanocompósitos de PHBV/NTC foram produzidos por mistura em solução, seguida de evaporação do solvente. Na produção dos PHBV/NTC, avaliou-se a utilização de banho de ultrassom, processador ultrassônico e a funcionalização dos NTC por reações de oxidação. Primeiramente, foi realizada a caracterização e a funcionalização dos NTC por dois métodos: oxidação com ácido nítrico (HNO3) e oxidação com peróxido de hidrogênio (H2O2), variando-se o tempo de reação. Após oxidação, os NTC foram abreviados como NTCOOH e caracterizados quanto à presença de grupos funcionais em sua superfície e danos causados em sua estrutura. Os NTCOOH obtidos na oxidação com HNO3 mostraram uma maior estabilidade térmica em comparação àqueles obtidos na oxidação com H2O2. A produção de carbono amorfo variou em função do tempo de oxidação para HNO3 e permaneceu constante para H2O2. Não foi verificada diferença significativa na quantificação de hidroxilas, carbonilas e carboxilas na superfície dos NTCOOH. A oxidação com HNO3 3 mol L por 12 horas mostrou-se mais apropriada para a produção dos nanocompósitos de PHBV/NTCOOH. Posteriormente, nanocompósitos de PHBV/NTC e PHBV/NTCOOH com 0,05 % (m/m) de NTC e de NTCOOH, respectivamente, foram produzidos utilizando banho de ultrassom. As análises de DSC mostraram que os NTC e NTCOOH agem como agentes nucleantes no processo de cristalização do PHBV e que o PHBV/NTC e PHBV/NTCOOH possuem o mesmo comportamento térmico. As micrografias de SEM mostraram uma boa adesão interfacial dos NTC e NTCOOH com a matriz de PHBV, e a formação de aglomerados menores no caso dos PHBV/NTCOOH, indicando que a oxidação dos NTC melhorou sua dispersão na matriz de PHBV. Finalmente, nanocompósitos de PHBV/NTC contendo 0,05, 0,50, 1,00, 1,50 e 2,00 % (m/m) de NTC e PHBV/NTCOOH 2,00 % (m/m) foram produzidos, utilizando processador ultrassônico para a dispersão dos NTC. Verificou-se que o efeito nucleante do NTC foi proporcional ao aumento de sua concentração nos PHBV/NTC e que o pequeno aumento de estabilidade térmica (~7 ºC) verificada não variou com a concentração de NTC. A utilização do processador ultrassônico melhorou acentuadamente a dispersão dos NTC nos nanocompósitos e a hidrofobicidade das superfícies dos PHBV/NTC aumentou em função da concentração de NTC. O nanocompósito de PHBV/NTC 1,50 % (m/m) apresentou os melhores resultados nos ensaios mecânicos de tração, com aumento de 48 % no módulo de elasticidade, 49 % na tensão na força máxima e menor perda de alongamento (37 %) em comparação ao PHBV puro. Essas melhorias não foram verificadas para o PHBV/NTC 2,00 % (m/m), mas foram verificadas para PHBV/NTCOOH 2,00 % (m/m), indicando que a oxidação dos NTC permitiu a obtenção de boas propriedades mecânicas para maiores concentrações de NTC. Um resultado muito importante desse trabalho foi a sua baixa adesão a coágulos sanguíneos (baixa Trombogenicidade) verificada para o PHBV/NTC, o que amplia a possibilidade de aplicação desses nanocompósitos na área médica
Abstract: This work has evaluated the effect of addition of multi walled carbon nanotubes (NTC) in the thermal and mechanical properties, morphology and hydrophobicity of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), the PHBV. The addition of carbon nanotubes could result in an improvement of PHBV properties, a natural polyester that due to its biodegradability and biocompatibility has an important application potential. Thus, nanocomposites of PHBV/NTC were produced by solution mixing, and then solvent casting. In the production of PHBV/NTC, we have evaluated the use of ultrasonic bath, ultrasonic processor and the functionalization of NTC by oxidation reactions, in the NTC dispersion in the PHBV matrix. First, we have performed the NTC characterization and functionalization by two methods: oxidation with nitric acid (HNO3) and oxidation with hydrogen peroxide (H2O2), at different reaction times. After oxidation, NTC (abbreviated as NTCOOH) were characterized for the presence of functional groups on their surface and the damage of their structure. The NTCOOH obtained from oxidation with HNO3 showed a higher thermal stability compared to those obtained in the H2O2 oxidation. The amorphous carbon production varied with the oxidation time to HNO3 and remained constant for H2O2. There was no significant difference in the quantification of hydroxyl, carbonyl and carboxyl groups on the surface of NTCOOH. The oxidation with HNO3 3 mol L for 12 hours was more suitable for the production of nanocomposites PHBV/NTCOOH. Subsequently, nanocompósitos of PHBV/NTC and PHBV/NTCOOH were produced using ultrasonic bath with 0.05 % (m/m) of NTC and NTCOOH, respectively. The DSC analysis showed that the NTC and NTCOOH act as nucleating agents and that the PHBV/NTC and PHBV/NTCOOH have the same thermal behavior. The SEM micrographs showed a good interfacial adhesion between the NTC and NTCOOH with PHBV matrix, and the formation of smaller agglomerates in the case of PHBV/NTCOOH indicated that oxidation of NTC improved their dispersion in the PHBV matrix. Finally, nanocomposites PHBV/NTC with 0.05, 0.50, 1.00, 1.50 and 2.00 % (m/m) of NTC and PHBV/NTCOOH with 2.00 % (w/w) were produced using ultrasonic processor for the NTC dispersion. It was found that the nucleating effect of NTC was proportional to increase of its concentration in the PHBV/NTC and the small increase observed in the thermal stability (~7°C) did not depended on the concentration of NTC. The use of ultrasonic processor greatly improved the dispersion of NTC in the nanocomposites and the hydrophobicity of the PHBV/NTC increases with increasing concentration of NTC. The nanocomposite of PHBV/NTC 1.50 % (w/w) showed the best results in tensile test, with 48 % increase in elastic modulus of, 49 % in maximum tensile strength and smaller decrease on elongation (37 %) compared to the pure PHBV. These improvements were not observed for PHBV/NTC 2.00 % (m/m) but were observed for PHBV/NTCOOH 2.00 % (m/m), indicating that oxidation of NTC allowed to obtain better mechanical properties for higher concentrations of NTC. A very important result in this work was the low adherence to blood clots (low thrombogenicity) verified for the PHBV/NTC 2.00 % (w/w), which extends the application of these nanocomposites in the medical field
Doutorado
Físico-Química
Doutor em Ciências

Du fait de leurs propriétés intrinsèques exceptionnelles, les nanotubes de carbone (CNTs) sont des matériaux bien adaptés pour renforcer les polymères thermodurcissables. Le nanocomposite multifonctionnel ainsi obtenu possède des propriétés électriques, thermiques et mécaniques sensiblement meilleures que le polymère seul, ce qui lui procure de nombreuses applications potentielles, et tout particulièrement dans le domaine de l’électronique ou de l’aéronautique. Le but de cette thèse de doctorat est orienté suivant deux axes. Il s’agit dans un premier temps de mettre au point un matériau nanocomposite avec des propriétés multifonctionnelles à partir de techniques d’élaborations efficaces. Puis dans un second temps, l’objectif consiste à proposer des alternatives permettant d’améliorer ces propriétés. Le premier chapitre de cette thèse établit une revue de l’état de l’art au sujet des matériaux qui ont été étudiés au cours de ce travail de recherche. Parmi ces matériaux, nous pouvons citer tout particulièrement les CNTs, les renforts hybrides nano/micrométriques constitués de CNTs et d’alumine, les polymères conducteurs électroniques et les polymères thermodurcissables. Il s’agit plus précisément de présenter pour chaque matériau les techniques d’élaboration, leurs structures et finalement leurs propriétés. Dans la seconde partie du manuscrit, nous décrivons en premier lieu les procédés d’élaboration permettant d’obtenir des nanocomposites conformes aux normes internationales. Ensuite, nous présentons les différentes techniques de caractérisation de ces nanomatériaux. Il s’agit notamment de déterminer les phénomènes de transports électriques et thermiques. Des techniques d’analyses supplémentaires permettent de mieux comprendre la structure des matériaux obtenus dans une gamme d’échelle allant de l’état macroscopique à l’atomique. Ainsi, nous avons eu recours à l’utilisation de la microscopie électronique à balayage et en transmission, et aussi la microscopie à force atomique (AFM). Différentes études spectroscopiques de types : Raman, perte d’énergie des électrons (EELS), photoélectrons X (XPS) fournissent des informations additionnelles sur ces matériaux. Les résultats obtenus sur ces nanocomposites en matière de transports électronique et thermique montrent que certaines améliorations sont nécessaires pour optimiser les propriétés multifonctionnelles de ces nanomatériaux. Nous avons concentré nos efforts sur les phénomènes physicochimiques à l’interface matrice/renfort. Par conséquent, nous avons décidé de modifier la surface des CNTs afin de favoriser la cohésion matrice/renfort, mais aussi et surtout, pour diminuer les résistances de contacts entre les CNTs lorsqu’ils sont distribués aléatoirement dans une matrice polymère. Le dernier chapitre de la thèse s’articule autour de la fonctionnalisation des CNTs par un polymère conducteur électronique (ECP). Dans un premier temps, nous avons mis au point des techniques électrochimiques permettant de déposer une couche homogène d’épaisseur nanométrique d’ECP à la surface des CNTs. Ce polymère conducteur et en même temps biocompatible est le polypyrrole (Ppy). La précision et l’efficacité de notre démarche sont démontrées par les différents outils de caractérisation, et tout particulièrement grâce à la microscopie électronique en transmission à haute résolution. Des études supplémentaires par AFM couplé à un résiscope ont montré l’évolution de la résistance électrique d’hybrides CNT-Ppy plus ou moins isolés. Dans une seconde partie, nous avons mis au point une méthode permettant de contrôler finement l’épaisseur de Ppy déposé à la surface des CNTs
Carbon nanotubes (CNTs) are ideal candidates to reinforce thermoset polymers due to their exceptional intrinsic properties. The resulting multifunctional nanocomposite has electrical, thermal and mechanical properties sensitively higher than pristine polymer. Therefore, this new material possesses various potential applications, and particularly in the domain of electronics and aerospace. The aim of this PhD thesis is oriented towards two directions. In the first one, we establish efficient techniques to produce composite materials with multifunctional properties. Then, the objective consists in the enhancement of these properties by proposing valuable alternatives to previous results cited in the litterature. In the first chapter, we present the state of the art research concerning the materials studied during this work. Among these, there are in particular: CNTs, hybrids constituted of CNTs and alumina microparticles, electronically conducting and thermoset polymers. Moreover, this chapter deals with the characteristics of each material, i.e. elaboration techniques, structures and properties. The second chapter of the manuscript contains first, the elaboration techniques allowing the synthesis of high quality nanocomposites according to international standards. Then, we analyze the properties of these nanomaterials, and particularly in terms of electrical and thermal transports. Further characterization procedures allow better understanding of the obtained structures in a domain ranging from macroscopic to atomic scales. This is realized using scanning/transmission electron microscopy, Raman spectroscopy, EELS, XPS, and AFM. Electrical and thermal conductivity measurements obtained on these new materials give prominence to the necessity of some improvements. Thereby, we have focused our research on the physico-chemical phenomena at the matrix/filler interface. We have proposed to modify the surface of CNTs, in order to favour the matrix/filler cohesion, but also and mainly to decrease contact resistances between the randomly distributed CNTs within the polymer matrix. Finally, the last chapter deals with the surface functionalization of CNTs using electrochemistry. First, we have implemented an accurate technique to deposit a nanometric layer of electronically conducting polymer on the surface of CNTs. This conducting polymer, namely polypyrrole (Ppy) is in the meantime biocompatible. The accuracy and efficiency of our approach are demonstrated through various characterization techniques, and particularly using transmission electron microscopy. Further studies using AFM coupled with a resiscope indicate the electrical resistance distribution performed on CNT-Ppy hybrids. In the second part of this chapter, we present our method to control precisely the thickness of the Ppy layer around the CNTs

Single walled carbon nanotubes (SWCNTs) are carbon based nanostructures with extraordinary electronical and mechanical properties. They are used in a wide range of applications, usually embedded in polymer as fillers to form polymer based nanocomposites, in order to affect the electronic behavior of the polymer matrix. However, as the nanotubes properties are directly dependent on their intrinsic structure, it is necessary to select specific nanotubes depending on the application. In addition, as randomly oriented CNTs (as Filler) embedded in the polymer matrix show lower electrical conductivity than expected, alignment of CNTs in the polymer matrix can help to improve the nanocomposite electrical conductivity. In this thesis, focus is placed on the electrical properties of the produced SWCNTs/Polymer nanocomposites. A simple patterning method called nanoimprint lithography is presented which allows the use of extremely low amounts of nanotubes in order to increase the electrical conductivity of isolated polymers such as polystyrene (PS). In addition, a flexible mold to pattern nanocomposite films, leading to the creation of conducting nanotube networks, resulting in Alignment of SWCNTs (from the bottom of the film to the top of the imprinted patterns) inside the polymer matrix. The project further investigated the effect of different imprint temperatures and pressures on the electrical conductivity of produced nanocomposite and a trend is found due to the variation of parameters. Finally an optimum imprint condition based on maximum achieved conductivity is suggested. During different steps of sample preparations, the samples were characterized by different microscopic and spectroscopic techniques such as Atomic Force Microscopy (AFM), optical microscopy, Spectroscopic Ellipsometer, electrical measurements and Raman spectroscopy.

Orientador: Eliana Aparecida de Rezende Duek
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: Nanocompósitos poliméricos exibem potencial para aplicações como biomateriais, pois podem melhorar as propriedades dos polímeros por meio da associação com nanoestruturas, resultando em um material com propriedades estruturais e funcionais superiores. O objetivo desse trabalho foi o desenvolvimento e posterior caracterização de nanocompósitos de poli (L-ácido lático) (PLLA) e nanotubos de carbono (NTC). Os NTC têm sido pesquisados para aplicações biomédicas devido às suas excelentes propriedades, entretanto, os NTC possuem características estruturais que podem causar toxicidade em ambiente biológico. Nesse trabalho, primeiramente foi aplicado um método para purificar os NTC por modificação química com objetivo de melhorar a dispersibilidade e diminuir os efeitos tóxicos. Posteriormente foram preparados os nanocompósitos na forma de membranas de PLLA com NTC em diferentes concentrações, utilizando o método de evaporação de solvente. Foram realizadas caracterizações morfológicas com microscopia eletrônica de varredura e microscopia de força atômica, estudo do comportamento térmico por calorimetria exploratória diferencial e microscopia ótica com luz polarizada, e ensaios mecânicos sob módulo de tração, análise dinâmico-mecânica e nanoindentação. Na última etapa foi realizado teste in vitro de cultura de células. Resultados indicaram aumento da rugosidade das amostras após a adição de NTC, o estudo do comportamento térmico revelou que o NTC atua como agente nucleante nos nanocompósitos, promovendo a formação de maior quantidade de núcleos cristalinos na matriz polimérica. As propriedades mecânicas indicaram aumento no módulo de elasticidade, alongamento e dureza nos nanocompósitos. Na análise biológica, os resultados obtidos comprovaram que, após a adição de NTC, as células foram capazes de aderir e sustentar a proliferação celular sobre as membranas, apresentando favorável citocompatibilidade
Abstract: Polymer nanocomposites exhibit potential for applications as biomaterials because they can improve the properties of polymers by combination with nanostructures, resulting in a material with superior structural and functional properties. The purpose of this work was the development and further characterization of poly (L-lactic acid) (PLLA) and carbon nanotubes (CNT) nanocomposites. CNTs have been investigated for biomedical applications due to their excellent properties, however, pristine NTC have structural characteristics that may cause toxicity in biological environment. In this work, a method to purify the NTC by chemical modification in order to improve the dispersibility and to reduce the toxic effects was firstly applied. Subsequently, PLLA/NTC nanocomposite membranes were prepared at different concentrations by solvent casting. Samples were characterized by scanning electron microscopy, atomic force microscopy, polarized optical microscopy, differential scanning calorimetry, dynamic mechanical analysis, tensile test, nanoindentation and X ray diffraction. In the last step, in vitro cell culture assay was performed. The results indicated an increase of the roughness of the samples after the addition of NTC. Thermal behavior study showed that the NTC act as a nucleation agent in nanocomposites, promoting the formation of a larger amount of crystal nucleous in the polymer matrix. Mechanical properties indicated an increase in elastic modulus, elongation and hardness in the nanocomposites. In biological testing, the results showed that, after addition of NTC, cells were able to adhere and sustain cellular proliferation on membranes and showed a favorable cytocompatibility
Doutorado
Materiais e Processos de Fabricação
Doutora em Engenharia Mecânica

Orientadores: Ana Flavia Nogueira, Maria Isabel Felisberti
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica
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Resumo: Nanocompósitos poliméricos baseados em nanotubos de carbono possuem um dos mais elevados potenciais tecnológicos devido à possibilidade de produção de materiais com destacadas propriedades mecânicas, alta condutividade elétrica em baixos teores (baixos limites de percolação), e boa processabilidade. São sistemas versáteis que podem apresentar propriedades excepcionais, as quais podem ser controladas pela alteração na proporção de seus componentes, permitindo que sejam moldados para atender à aplicação exigida. Nesse trabalho, nanocompósitos de nanotubos de carbono de paredes múltiplas (MWCNTs) e um elastômero comercial (Kraton-D®), que é um copolímero em bloco de estireno-butadieno-estireno (SBS), foram preparados por extrusão e pela técnica de evaporação de solvente (casting). As propriedades térmicas, mecânicas, e elétricas desses materiais foram comparadas. A caracterização foi realizada através de medidas de condutividade elétrica (método de Coleman), microscopias eletrônicas de varredura e de transmissão (caracterização morfológica), termogravimetria (determinação do teor de cargas e estabilidade térmica), ensaios de tração e análise dinâmico-mecânica (propriedades mecânicas). Além disso, o potencial de aplicação dos compósitos em células solares de TiO2/corante (DSSC) e como materiais absorvedores de radiação (MAR) foi avaliado. Os resultados evidenciaram uma forte influência da metodologia de preparo nas propriedades finais dos compósitos, a qual é creditada a mudanças de morfologia do sistema em função das condições de preparação utilizadas. As amostras preparadas por casting apresentaram condutividades elétricas mais elevadas, enquanto as propriedades mecânicas foram superiores para os filmes extrudados, e ambas tiveram melhoria da estabilidade térmica. Os compósitos se mostraram promissores quanto ao uso em DSSC e como MAR, mas muitos estudos ainda são necessários para aprimorar sua eficiência nesses campos
Abstract: Polymeric nanocomposites based on carbon nanotubes (CNTs) have one of the highest technological potential due to the possibility of produce materials with improved mechanical properties, high electrical conductivity at low loadings (low percolation threshold), and good processability. These systems are versatile, may present astonishing properties, and are allowed to control them by changing the proportion of their components, being able to tailor these materials to suit a desired application. In this work, nanocomposites of multiwalled carbon nanotubes (MWCNTs) and a commercial elastomer (Kraton-D®), which is a block copolymer of styrenebutadiene- styrene (SBS), were prepared by extrusion and by casting. The thermal, mechanical, and electrical properties presented by these materials were compared. The characterization was performed by measurement of the electrical conductivity (Coleman¿s method), scanning and transmission electron microscopy (for morphologic characterization), thermogravimetry (for thermal stability and determination of the loading of filler), stress-strain tests and dynamic mechanical analysis (for the mechanical properties). Furthermore, the potential of application of the extruded composites in dye-sensitized solar cells (DSSC) and as radiation absorbing materials (RAM) was tested. The results showed a strong influence of the methodology of preparation upon the final properties of composites, which was attributed to changes in the morphology of the system with conditions used to prepare the samples. Composites made by casting showed a higher electrical conductivity than the extruded ones, although the latter presented better mechanical properties than the former ones. Despite the requirement of further studies to improve their efficiency in DSSC and as RAM, the composites were promising for these applications
Mestrado
Quimica Inorganica
Mestre em Química

Carbon nanotube–polymer nanocomposites have been the centre of intense studies for the past few years. With the superior properties of carbon nanotubes and the flexibility of polymers for different applications, extremely high expectations were set for this class of nanocomposites. Modelling studies showed significant potential, but the experimental investigations faced strict challenges to reach the predicted values. One of the main challenges is to obtain the optimum interaction between the nanotubes and the polymer matrix. The interaction influences the dispersion of nanotubes in the polymer and affects the overall properties of the nanocomposite. Therefore, the main objective of this research was to study the carbon nanotube–polymer interaction in nanocomposites. Based on a comprehensive review of the literature, molecular dynamics and atomic force microscopy were selected as the modelling and experimental techniques to study the interaction. In the modelling section, the interfacial properties of a single-walled carbon nanotube–poly(methyl methacrylate) nanocomposite were obtained through a three-phase simulation of a pull-out test. An interfacial binding energy of 0.39 kcal/molÅ2 was obtained from molecular dynamics simulation. On the other hand, in the experimental section, stepwise discretization method was proposed as a novel technique of interaction measurement using atomic force microscopy. Furthermore, a new interaction parameter, called interaction stress, was introduced to evaluate the interaction quality in nanocomposites. The stepwise discretization method was applied to a single-walled carbon nanotube–poly(methyl methacrylate) nanocomposite and a maximum interaction stress of 7 MPa was obtained. The results were, then, applied to classical contact theory and a nanoscale contact theory was developed. Furthermore, the interaction stress data were input to coarse grain simulations to obtain the interfacial properties of the nanocomposites. This new approach benefited from the flexibility of the coarse grain method and the reliability of the experimental data obtained from atomic force microscopy. Based on the results of the coarse grain simulations, the interfacial binding energy of a single-walled carbon nanotube–poly(methyl methacrylate) nanocomposite was estimated as 0.44 kcal/molÅ2. This value was then compared with the interfacial binding energy obtained from molecular dynamics results (i.e., 0.39 kcal/molÅ2). The good agreement between the results of modelling and experimental approaches demonstrated the validity of the work and the robustness of the proposed methods and parameters.
Les nanocomposites avec des polymères renforcés de nanotubes de carbone ont été le centre d'attention de nombreuses études dans les dernières années. Les propriétés supérieures des nanotubes de carbone et la flexibilité des polymères à être utilisés dans de diverses applications ont créé de grandes attentes pour cette classe de nanocomposites. Des études de modélisation ont démontré un fort potentiel pour ces matériaux, cependant la validation expérimentale de ces propriétés prédites reste un défi. Une des principales difficultés est l'obtention d'une interaction optimale entre les nanotubes et la matrice polymère. Cette interaction influence la dispersion des nanotubes dans le polymère et affecte les propriétés globales du nanocomposite. De ce fait, l'objectif principal de ce travail de recherche a été l'étude de l'interaction entre les nanotubes de carbone et le polymère dans les nanocomposites. A partir d'une revue détaillée de la littérature, la méthode de dynamique moléculaire et la microscopie à force atomique ont été choisies comme techniques numériques et expérimentales pour étudier l'interaction. Dans la partie de modélisation, les propriétés d'interface d'un nanotube à paroi simple avec du poly(methyl methacrylate) ont été obtenues à partir d'une simulation d'un test d'arrachement en trois phases. Une énergie de liaison d'interface de 0.39 kcal/molÅ2 a été calculée par la simulation de dynamique moléculaire. Dans la section expérimentale, une méthode de discrétisation par étapes a été proposée en tant que nouvelle technique de mesure de l'interaction par microscopie à force atomique. De plus, un nouvel paramètre d'interaction, appelé contrainte d'interaction, a été introduit pour évaluer la qualité de l'interaction dans les nanocomposites. La méthode de discrétisation par étapes a été utilisée pour le nanocomposite de poly(methyl methacrylate) avec un nanotube de carbone à paroi simple, et une interaction maximale de contrainte de 7 MPa a été obtenue. Les résultats ont été ensuite utilisés pour la théorie classique de contact et une théorie de contact à l'échelle nano. Les données sur les interactions de contraintes ont été aussi utilisées comme entrées pour des simulations de dynamique moléculaire «gros grains» afin d'obtenir les propriétés d'interface des nanocomposites. Cette nouvelle approche bénéficie de la flexibilité de la méthode de dynamique moléculaire «gros grains» et de la fiabilité des données expérimentales obtenues par la microscopie à force atomique. À partir des résultats de la méthode de dynamique moléculaire «gros grains», l'énergie de liaison d'interface d'un nanocomposite de nanotube de carbone–poly(methyl methacrylate) a été estimée à 0.44 kcal/molÅ2. Cette valeur a été comparée à l'énergie de liaison d'interface obtenue par la méthode de dynamique moléculaire (i.e., 0.39 kcal/molÅ2). La bonne corrélation entre les résultats basés sur des approches numériques et expérimentales démontre la validité de cette étude ainsi que la robustesse des méthodes proposées et des paramètres développés.

A commercial unsaturated polyester resin has been used in combination with commercial multiwalled carbon nanotubes (MWNTs) to study the effects of this nanofiller on the electrical properties of the mix in the liquid state, during the cure and in the solid state. The level of addition of the nanotubes ranged from 0.05 to 0.3 wt%. The dispersion of the filler particles in the matrix was carried out combining triple roll milling, horn sonication and high shear mixing. Qualitative optical and electronic microscopy characterisation supports the development of novel techniques for real-time quantitative assessments of dispersion quality. Fitting of shear dependent viscosity, measured between 0.1 and 100 s-1, to Carreau's model has been shown to provide an indicator of the state of nanotube dispersion in the mixture. Additionally, liquid electrical conductivity measurements offer the option of on-line monitoring, providing a promising tool for process optimisation. The formation of an effective conductive network of nanotubes during the cure was investigated by combining impedance spectroscopy measurements and equivalent circuit modelling with two parallel RC circuit in series with each other. This allows in-situ observation of the key phenomenon responsible for the electrical conductivity of the nanocomposite, namely the filler re-aggregation during cure. Optimisation of dispersion and cure parameters results in a nanocomposite showing conductive behaviour in the solid state, achieving DC conductivity of 0.13 S/m at 0.30 wt% loading. The percolation threshold was estimated to occur at 0.026 wt% filler loading. The conductivity achieved is comparable to state-ofthe-art epoxy thermosetting nanocomposites based on use of carbon nanotubes of equivalent quality. Successful laboratory scale trials demonstrated the suitability of the materials in copper electroplating and resistance heating. An industrial scale up trial of a 40 kg batch was carried out, using the dispersion and the monitoring techniques developed in the study.