The advancement of each component of aerospace vehicles is necessary as the continual demand for more aggressive missions are created. Improvements in propulsion and guidance system electronics are invaluable; however without material development to protect the vehicle from its environment those advances will not have a practical application. Thermal protection systems (TPS) are required in both external applications; for example on reentry vehicles, as well as in internal applications; to protect the casing of rockets and missiles. This dissertation focuses on a specific type of internal solid rocket motor TPS, ablatives. Ablatives have been used for decades on aerospace vehicles. To protect the motor from the hostile environment, these materials pyrolyze and char. Both of these mechanisms produce a boundary between the combustion gases and the motor as well as release the heat that the decomposed material has absorbed. These sacrificial materials are intended to protect the casing that it is attached to. With the development of polymer nanocomposites (PNCs) in the last couple of decades, it is of interest to see how these two fields can merge. Three different nanomaterials (carbon nanofibers, multiwall carbon nanotubes, and nanoclays) are examined to observe how each behaves in environments that simulate the motor firing conditions. These nanomaterials are individually added to a thermoplastic polyurethane elastomer (TPU) at different loadings, creating three distinct families of polymer nanocomposites. To describe a materials ablative performance, a number of material properties must be individually studied; such as thermal, density, porosity, char strength, and rheology. Different experiments are conducted to isolate specific ablative processes in order to identify how each nanomaterial affects the ablative performance. This dissertation first describes each material and the ablative processes which are characterized by each experiment. Then basic material properties of each family of materials are described. Degradation and flammability experiments then describe the degassing processes. Studies of the material char are then performed after full blown rocket experiments are done. These tests have shown that of the three nanomaterials, nanoclay enhances the TPU ablative performance the most while the CNF provides the least enhancement. / text

One of the important dynamic parameter characterizing the properties of polymer nanocomposite is viscosity. It is a quantity of interest on macroscopic scale also. A thorough study of viscosity in case of polymer nanocomposite has not been carried out in the existing literature. In this work we used atomic force microscope, force-distance spectroscopy to experimentally measure the viscosity of polymer and polymer nanocomposite thin films. In particular we try to tune viscosity by changing the nature of interface of polymer grafted nanoparticle and polymer melt. The interface nature in varied by changing the miscibility parameter ( f ), defined as the ratio of grafted chain length to the matrix chain length. Using coarse-grained molecular dynamic simulations, dynamics at the nanoparticle-matrix interface is explored by calculating slip length and mobility at the interface. Equilibrium molecular dynamic simulation is employed to calculate the viscosity of nanocomposite. Chapter 1 We introduce some basic models for polymer chain conformation and dynamics. The known facts about the structural and dynamics of polymer grafted nanoparticle are also described. Chapter 2 We present our experiment method and results for various nanocomposite systems for two different volume fractions of nanoparticles and for two different thicknesses. We show that introduction of nanoparticles causes reduction in viscosity of thin film with respect to the neat polymer films. Further for the low volume fraction system (0:5%) the extent of reduction decreases with increasing f -value and almost matching the neat system at the highest f . At high volume fraction (1%), for lower f we observe a reduction in viscosity and for highest f surprisingly there is an increase in viscosity of nanocomposite with respect to the neat system with a cross-over for intermediate f . We attribute the effects to possible slip at the nanoparticle-matrix interface. A rough estimation of slip length from the measured value of viscosity of nanocomposite and pure polymer is provided which strongly supports our idea of slip at the interface Chapter 3 Briefly discusses some basic aspects of molecular dynamic simulation. Chapter 4 Using MD simulation we calculate the slip-length at the grafted nanoparticle-matrix interface for various systems with different f values. A spherical core grafted with atoms same as the matrix is kept fixed at the canter of simulation box. The particle is rotated for calculating slip length. We also look at the mobility variation of matrix chains as a function of radial distance from the centre of nanoparticle. From both slip-length and mobility calculation we observe that slip length as well as mobility is higher for lower f systems as compared to higher f thus supporting our assertion of slip as the most likely cause for our experimental observations. Chapter 5 Now instead of single grafted nanoparticle we have multiple nanoparticles which are free to move in the matrix. Using Green-Kubo formalism we calculate the equilibrium viscosity for pure polymer and nanocomposite systems from MD simulations. We observe increase in viscosity for nanocomposite system as compared to the pure polymer system. We also look at various structural and dynamical changes, that occurs in the filled system with respect to neat system, that leads to such increase in viscosity.

Composites based on ICP with conductive (SWCNT and Te) and insulating fillers (TiO2 and CuO and insulating polymers with conducting fillers (rGO, modified rGO, and SWCNT) were prepared and their thermoelectric properties were investigated. Attempts to enhance the thermoelectric properties of PEOT:PSS composites did not bring about a significant change. But, the attempts to modify rGO brought about a considerable improvement in the thermoelectric properties. At the end, the use of SWCNT provided the maximum ZT in case of insulating polymer composites. Eventually, SEBS/4 wt% SWCNT with a ZT of 0.0017 and SBS/0.5 wt% SWCNT with a ZT 6  10-6 stood out as the best p-type and n-type thermoelectric material, respectively, in this work. This success paved the way to build 2 modules of thermoelectric generators which generated a maximum potential of 93.2 mV at a temperature difference of 40 K.

No description available.

Nanostructured porous materials generally, and nanoporous noble metals specifically, have received considerable attention due to their superior chemical and physical properties over nanoparticles and bulk counterparts. This dissertation work aims to develop well-established strategies for the preparation of multifunctional nanostructured porous materials based on the combination of inorganic-chemistry, organic-chemistry and electrochemistry. The preparation strategies involved one or more of the following processes: sol-gel synthesis, co-electrodeposition, metal ions reduction, electropolymerization and dealloying or chemical etching. The study did not stop at the preparation limits but extended to investigate the reaction mechanism behind the formation of these multifunctional nanoporous structures in order to determine the different factors controlling the nanoporous structures formation. First, gold-silica nanocomposites were prepared and used as a building blocks for the fabrication of high surface area gold coral electrodes. Well-controlled surface area enhancement, film thickness and morphology were achieved. An enhancement in the electrode’s surface area up to 57 times relative to the geometric area was achieved. A critical sol-gel monomer concentration was also noted at which the deposited silica around the gold coral was able to stabilize the gold corals and below which the deposited coral structures are not stable. Second, free-standing and transferable strata-like 3D porous polypyrrole nanostructures were obtained from chemical etching of the electrodeposited polypyrrole-silica nanocomposite films. A new reaction mechanism was developed and a new structural directing factor has been discovered for the first time. Finally, silver-rich platinum alloys were prepared and dealloyed in acidic medium to produce 3D bicontinuous nanoporous platinum nanorods and films with a nanoporous gold-like structure. The 3D-BC-NP-Pt displayed high surface area, typical electrochemical sensing properties in an aqueous medium, and exceptional electrochemical sensing capability in a complex biofouling environment containing fibrinogen. The 3D-BC-NP-Pt displayed high catalytic activity toward the methanol electro-oxidation that is 30 times higher that of planar platinum and high volumetric capacitance of 400 F/cm3. These findings will pave the way toward the development of high performance and reliable electrodes for catalysis, sensing, high power outputs fuel cells, battery-like supercapacitors and miniaturized device applications.

Ce travail concerne l'étude du comportement rhéologique de nanocomposites modèles à base de Laponite dans du polyoxyde d'éthylène ou des mélanges polyoxyde d'éthylène avec du polyméthacrylate de méthyle. L'influence des paramètres moléculaires, masse molaire de la matrice et mode de protection des particules sur les propriétés rhéologiques a été étudiée. La meilleure dispersion est obtenue à partir d'une solution, la dilution d'un mélange maître conduisant à des matériaux hétérogènes. Les mélanges POE/PMMA sont compatibles à l'état fondu dans toute la gamme de concentrations mais hétérogènes à température ambiante au-dessus de 30% en poids de particules. En diluant un mélange Laponite/PEO dans le PMMA, nous avons montré que ces domaines se concentrent en particules en dessous de 30% de PEO et qu'une cocontinuité de phases PEO contenant les particules et PMMA essentiellement pur est formée au-dessus de 30% de PEO. La présence des particules diminue fortement la cristallinité. / This study concerns model nanocomposites based on Laponite and polyethylene oxide, alone or blended with polymethylmethacrylate. We studied the influence of the parameters on rheological properties of model PEO/Laponite nanocomposites such as matrix molecular weight, preparation method. The best dispersion state of the particles is obtained from solution. Melt dispersion leads to a low frequency modulus which depends on the length and grafting density of the particles. Heterogeneous materials are obtained from melt dispersion of a master batch. PMMA/PEO blends appear to be homogeneous at room temperature only for PEO concentration less than 30wt%. Laponite particles are concentrated in small domains where most of PEO has been extracted. At higher concentrations of PEO, a continuous phase containing PEO and Laponite above percolation concentration is observed, leading to an elastic modulus at low frequency. The presence of Laponite decreases significantly the crystallinity of PEO.

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

The current study discusses the preparation and long-term performance of polymer composites used for various purposes under different ageing conditions. The first part deals with the preparation and characterization of polymer nanocomposites based on poly(ethylene-co-butyl acrylate) (EBA–13 and EBA–28 with 13 and 28 wt % butyl acrylate, respectively) and 2–12 wt % (0.5–3 vol %) of aluminum oxide nanoparticles (two types with different specific surface areas and different hydroxyl-group concentrations; uncoated and coated with, respectively, octyltriethoxysilane and aminopropyltriethoxysilane). The nanocomposite with EBA–13 showed better overall nanoparticle dispersion while EBA–28 resulted in poor dispersion, probably due to insufficiently high shear forces acting during extrusion mixing which were unable to break down nanoparticle agglomerates. The activity of hindered phenolic antioxidant (0.2 wt%) in all EBA nanocomposites was assessed by determining the oxidation induction time using DSC. The composites containing uncoated aluminium oxide nanoparticles showed a much shorter initial OIT than the pristine polymer with the same initial concentration of antioxidant, indicating adsorption of antioxidant onto the nanoparticle surfaces. Composites containing coated nanoparticles showed a significantly smaller decrease in the initial OIT, suggesting the replacement of hydroxyl groups with organic silane tails, decreasing the concentration of available adsorption sites on the nanoparticle surfaces. The decrease in OIT with increasing ageing time in dry air at 90 °C of the nanocomposites was slower than that of the unfilled pristine polymer, suggesting a slow release of antioxidant from adsorption sites. The EBA nanocomposites exposed to liquid water at 90°C showed faster decrease of OIT than samples exposed to dry or humid air. The migration rate of antioxidant was controlled by the boundary conditions in the case of ageing in humid air and liquid water. The antioxidant diffusivity was lower for the composites containing uncoated ND than for the composites containing ND coated with octyltriethoxysilane or aminopropyltriethoxysilane. The migration and chemical consumption of deltamethrin DM, (synthetic pyrethroid) and synergist piperonyl butoxide from molded polyethylene sheets was also studied. Deltamethrin and piperonyl butoxide are often used for food  storage and insect control purposes. DM showed no signs of crystallization and remained in a liquid state after being cooled to room temperature. Exposure of polyethylene compound sheets to liquid water (at 80 &amp; 95 °C), caused degradation and hydrolysis of the ester bond in the DM, present in the prepared material, and generated species containing hydroxyl groups. Liquid chromatography and infrared spectroscopy showed a significant migration of the active species in liquid water, whereas in air at 80 °C (60 and 80 %RH) the loss of DM and PBO was negligible over 30 days. The long-term performance of medium-density polyethylene stabilized with six different phenolic antioxidants (0.1 wt%) in aqueous chlorinated media at 70 °C was studied. The results were compared with data for previously studied solutions of antioxidants in squalane (a liquid, low molar mass analogue of polyethylene). A linear relationship was established between the time to reach antioxidant depletion in polyethylene tape samples and the time in squalane samples. Infrared spectroscopy and scanning electron microscopy of drawn samples revealed the onset of surface oxidation and surface embrittlement in tape samples exposed beyond the time for antioxidant depletion. / <p>QC 20121109</p> / Cable insulation materials / Loss of deltamethrin and pipronyl butoxide from polyethylene / long-term performance of polyethylene in chlorine dioxide water

This work describes the production and characterization of colloidal solution of silver nanoparticles (AgNPs) and insertion of this colloidal solution in a polymeric ma-trix of epoxy resin. The first stage of this work was the preparation of AgNPs in colloi-dal solution, using AgNO3 as the precursor, ethylene glycol as a medium and dispersant sodium citrate as reducing agent and stabilizer. Were also measured the temporal sta-bility of the solution of AgNPs for possible use over time. The colloidal solution of Ag-NPs was characterized by UV-Vis, DLS (dynamic light scattering) and Zeta potential and through its measures. We found that the colloidal solution of AgNPs is composed of stable nanoparticles, and spherical with average diameter around 10 to 12 nm. In the second stage the preparation and characterization of polymeric matrix of epoxy resin with different solution concentrations (2 ml, 5 ml, 8 ml and 10 ml) of AgNPs inseted manually into the matrix. Structural characterization of components of the polymeric matrix was performed using the techniques of FTIR spectroscopy (Fouri-er transform infrared) and Raman. The indication of the presence of AgNPs and their state of dispersion in the epoxy matrix was studied by UV-Vis spectroscopy and TEM (transmission electron microscopy), and through the results showed the presence of nanoparticles in a dispersed and an average size around 50 nm. Thermogravimetric analysis (TGA) to check the maximum thermal stability of nanocomposite were per-formed. The TGA results indicated that the degradation temperature of the polymer underwent a slight decrease with increasing the volume of solution to resin AgNPs in-serted. In addition, analysis was performed microhardness of the epoxy resin produced with different concentrations of AgNPs solution and subjected to heat treatment. Ac-cording to the microhardness tests, the presence of ethylene glycol in the epoxy matrix significantly altered their microhardness values, acting as a plasticizer. / Neste trabalho descreve-se a produção e caracterização de solução coloidal de nanopartículas de prata (AgNPs) e a inserção dessa solução coloidal em uma matriz polimérica de resina epóxi. A primeira etapa desse trabalho consistiu na síntese de AgNPs em solução coloidal, utilizando AgNO3 como o precursor, o etilenoglicol como meio dispersante e o citrato de sódio como agente redutor e estabilizante. Também foram realizadas medidas de estabilidade temporal da solução de AgNPs, para possí-veis usos ao longo do tempo. A solução coloidal de AgNPs foi caracterizada pela espec-troscopia UV-Vis, DLS (espalhamento dinâmico da luz) e potencial Zeta, e através de suas medidas, constatou que a solução coloidal de AgNPs foi composta de nanopartí-culas estáveis, esféricas e com diâmetro médio em torno de 10 12 nm.Na segunda etapa foi realizada a preparação e caracterização de matriz polimé-rica de resina epóxi com diferentes concentrações (2 ml, 5 ml, 8 ml e 10 ml) de solução de AgNPs inseridas manualmente à matriz. A caracterização estrutural dos componen-tes da matriz polimérica foi realizada utilizando-se as técnicas de espectroscopia por FTIR (infravermelho por transformada de Fourier) e Raman. A indicação da presença das AgNPs e do seu estado de dispersão na matriz epóxi foi estudado empregado a espectroscopia UV-Vis e MET (microscopia eletrônica de transmissão), e por meio dos resultados, constatou-se a presença das nanopartículas de forma dispersa e com um tamanho médio em torno de 50 nm. Foram realizadas análises termogravimétricas (TGA) para verificar a estabilidade térmica da resina epóxi. Os resultados de TGA indi-caram que a máxima temperatura de degradação do polímero sofreu uma leve redu-ção com o aumento do volume de solução de AgNPs inserida à resina. Além disso, também foram realizadas análises de microdureza Vickers da resina epóxi produzida com diferentes concentrações de solução de AgNPs e submetidas a tratamento térmi-co. De acordo com os ensaios de microdureza, a presença do etilenoglicol na matriz epóxi alterou significativamente seus valores de microdureza, atuando como plastifi-cante.

Title: Modification of polymeric substrates by means of non-equilibrium plasma Author: Anna Kuzminova Department: Department of Macromolecular Physics Supervisor of the doctoral thesis: doc. RNDr. Ondřej Kylián, Ph.D. Abstract: Processing of polymeric materials by means of non-equilibrium plasma is a topic that reaches increasing attention, which is due to the wide range of possible applications. As an example can be mentioned processing of polymeric foils used for food packaging, where plasma treatment enables to improve their functional properties (e.g. increase their printability or enhance their barrier properties). In the frame of this PhD. thesis two different strategies suitable for the modification of polymeric materials were followed. The first one was based on treatment of polymers by atmospheric plasma. The main attention was devoted to the investigation of influence of atmospheric pressure plasma on surface properties of 8 commonly used polymers, namely on their chemical composition, morphology and wettability. In addition, it was observed that plasma treatment causes also alteration of their mechanical properties, may lead to their substantial etching and in some cases improves their biocompatibility. The second studied strategy was based on coating of polymers with thin functional...