Small concentrations of graphene can significantly alter the phase behavior and the mechanical and electrical characteristics of polymeric materials. In this Masters thesis, we present results from a hierarchical simulation methodology that leads to the prediction of the thermodynamic, conformational, structural, dynamic and mechanical properties of polymer nanocomposites. As a model system, we have chosen syndiotactic poly(methyl methacrylate) or sPMMA reinforced with uniformly dispersed graphene sheets. How graphene functionalization affects the elastic constants of the resulting nanocomposite is also examined. The simulation strategy entails three steps: 1) Generation of an initial structure which is subjected to potential energy minimization and detailed molecular dynamics (MD) simulations at T=500K and P=1atm, to obtain well relaxed melt configurations of the nanocomposite and to extract any interested properties. Furthermore, for the sPMMA/graphene nanocomposite: 2) Gradual cooling of selected configurations down to room temperature to obtain a good number of structures representative of its glassy phase, and 3) Molecular mechanics (MM) calculations of its mechanical properties following the method originally proposed by Theodorou and Suter. The MD simulations have been executed with the LAMMPS code using the all-atom DREIDING force-field. By analyzing MD trajectories under constant temperature and pressure, all nanocomposite systems were found to exhibit slower terminal and segmental dynamics than the unfilled ones. The addition of a small fraction of graphene sheets in the polymer matrix led to the enhancement of its elastic constants especially when functionalized graphene sheets were used. / Μικρές συγκεντρώσεις γραφενίου μπορούν να τροποποιήσουν σημαντικά τη φασική συμπεριφορά και τα μηχανικά και ηλεκτρικά χαρακτηριστικά των πολυμερικών υλικών. Στη παρούσα εργασία παρουσιάζουμε αποτελέσματα από μία ιεραρχική μεθοδολογία προσομοίωσης που οδηγεί στη πρόβλεψη των θερμοδυναμικών, δομικών, δυναμικών και μηχανικών ιδιοτήτων πολυμερικών νανοσύνθετων υλικών. Σαν σύστημα μοντελοποίησης, επιλέξαμε τον συνδιοτακτικό πολυμεθακρυλικό μεθυλεστέρα, syndiotactic poly(methyl methacrylate), ή sPMMA, ενισχυμένο με ομοιόμορφα διεσπαρμένα φύλλα γραφενίου. Επίσης εξετάζεται και το πώς η χημική τροποποίηση του γραφενίου επηρεάζει τις ελαστικές ιδιότητες του νανοσύνθετου υλικού. Η στρατηγική της προσομοίωσης των συστημάτων συνοψίζεται σε τρία βήματα: 1) Δημιουργία αρχικών απεικονίσεων οι οποίες υποβάλλονται σε ελαχιστοποίηση της δυναμικής τους ενέργειας και στη συνέχεια σε λεπτομερείς προσομοιώσεις Μοριακής Δυναμικής (MD) σε T=500K και P=1atm, ώστε να εξαγάγουμε πλήρως χαλαρωμένες διαμορφώσεις τήγματος του νανοσύνθετου υλικού και να υπολογίσουμε ιδιότητες που μας ενδιαφέρουν. Επιπλέον για τα νανοσύνθετα υλικά sPMMA/γραφενίου συνεχίζουμε με 2) Σταδιακή ψύξη επιλεγμένων ατομιστικών διαμορφώσεων σε θερμοκρασία δωματίου με σκοπό την εξαγωγή ενός ικανοποιητικού αριθμού δομών, αντιπροσωπευτικών της υαλώδους φάσης τους, και 3) Εφαρμογή της μεθόδου της Μοριακής Μηχανικής (MM) για τον υπολογισμό των μηχανικών ιδιοτήτων τους ακολουθώντας τη μέθοδο που προτάθηκε από τους Θεοδώρου και Suter. Οι προσομοιώσεις της Μοριακής Δυναμικής πραγματοποιήθηκαν με τη χρήση του κώδικα LAMMPS, εφαρμόζοντας το DREIDING πεδίο-δυνάμεων και υιοθετόντας το μοντέλο των διακριτών ατόμων για την περιγραφή των ατομιστικών αλληλεπιδράσεων των συστημάτων. Αναλύοντας τις τροχιές των ατόμων από τις προσομοιώσεις της Μοριακής Δυναμικής υπό σταθερή θερμοκρασία και πίεση, τα υπό μελέτη νανοσύνθετα συστήματα βρέθηκαν να παρουσιάζουν βραδύτερη ολική και τοπική δυναμική σε σχέση με το καθαρό πολυμερές. Η προσθήκη μικρών κλασμάτων φύλλων γραφενίου στην πολυμερική μήτρα οδήγησε στην ενίσχυση των ελαστικών ιδιοτήτων της και σε μία περαιτέρω βελτίωση αυτών, όταν χρησιμοποιήθηκαν χημικώς τροποιημένα φύλλα γραφενίου.

Dans l'industrie du pneumatique, l'incorporation de nanoparticules de silice dans les élastomères permet d'obtenir des pneumatiques avec des propriétés mécaniques améliorées. D'un point de vue fondamental, deux contributions sont communément invoquées pour expliquer ces changements : (i) une contribution du réseau de charges, fortement dépendante de leur état de dispersion, (ii) une contribution des chaines dont la conformation est potentiellement modifiée en présence du réseau de charges. Cependant, les mécanismes permettant de relier cette structure nanométrique aux propriétés macroscopiques du matériau sont encore mal compris. Dans ce contexte, nous avons synthétisé des systèmes SBR/Silice modèles constituant une première approche de systèmes industriels plus complexes. En modifiant les conditions de dispersion au moyen d'agent de greffage, nous avons obtenu des nanocomposites avec des dispersions variées et reproductibles, avec des organisations multi-échelle. Celles-ci ont été caractérisées finement par l'utilisation combinée de la Diffusion de Rayons X aux Petits Angles (DXPA) et de la Microscopie Electronique en Transmission (MET). La conformation des chaines, déterminée expérimentalement par Diffusion de Neutrons aux Petits Angles (DNPA), n'est pas affectée par un effet à longue distance des charges. La caractérisation quantitative de la dispersion a permis de mettre en évidence le rôle prépondérant de la compacité des agrégats de silice et de la densité de leur réseau sur le renforcement dans le régime élastique.

In this work the electrical insulating properties of the nanocomposite materials based on poly(ethylene-co-butyl acrylate) filled with alumina nanoparticles are studied. The dielectric properties chosen for the evaluation are the dielectric permittivity and loss as well as the breakdown strength and the pre-breakdown currents. The reason for choosing these particular properties is partly due to the importance of these for the general electrical applications and partly due to the uncertainties involved for these particular properties of the nanocomposite materials. The importance of moisture absorption for the dielectric properties is outlined in this work. All measurements were performed in both dry conditions and after conditioning of the materials in humid environment until saturation. The data for moisture absorption was taken from the water absorption study performed at the Department of Fibre and Polymer Technology, KTH. The dielectric spectroscopy in frequency domain was employed for measuring dielectric permittivity and loss. Havriliak-Negami approximation was used for characterization of the measurement data and at the same time ensuring the fulfillment of the Kramers-Kronig relations. Results from the dielectric spectroscopy study in dry conditions suggest that dielectric spectroscopy can be used for evaluating nanoparticle dispersion in the host matrix, based on correlation between the morphology data obtained from SEM investigation and the scatter in the dielectric loss. The dielectric spectroscopy study performed on the nanocomposites after conditioning in humid environment showed that absorbed moisture has a distinct impact on the dielectric loss. Especially pronounced is its’ influence on the frequency behavior, when the dielectric loss peaks are shifted towards higher frequencies with increased moisture content. The nanocomposite materials characterized by higher specific surface area generally exhibit higher dielectric losses. Surface functionalization of the nanoparticles does not seem to have much influence on the dielectric loss in dry conditions. After conditioning in humid environment, however, the surface modification was shown to have a significant impact. Temperature is another significant factor for the frequency behavior of the dielectric loss: it was found that the studied nanocomposites can be characterized by Arrhenius activation. The breakdown strength and pre-breakdown currents study outlined the influence of moisture as well. The study indicated that surface treatment of the nanoparticles can enhance properties of the nanocomposite materials, namely aminopropyltriethoxy silane was an especially successful choice: • The highest breakdown strength was determined by the study for NDA6 material formulation in dry conditions. • After conditioning in humid environment the NDA6 material continued showing the best breakdown strength among the nanocomposite mate rials, as well as this value was close to the breakdown strength of the reference unfilled material. This study confirms the existence of the optimal nanofiller content or rather optimal specific surface area of the dispersed nanoparticles in the host matrix. The latter is supported by the comparison between the nanocomposites based on nanoparticles with two different specific surface areas, which shows that the dielectric properties worsen, i.e. the dielectric losses increase and the influence of absorbed moisture on the breakdown strength becomes more pronounced, for nanomaterials with larger specific surface area. The pre-breakdown currents were found to follow space-charge limited conduction mechanism reasonably well. The following conduction regimes were identified: constant region (likely due to measurement difficulties at low field strengths), Ohm’s regime, trap-filled-limit regime and trapfree dielectric regime. The breakdown usually occurred either during the trap-filled-limit regime, when the current increased dramatically for the small change in electric field, or during the trapfree dielectric regime. The threshold values between different conduction regimes seem to correlate well with the oxidation induction times (OIT), which in turn depend on the total specific surface area. The pre-breakdown currents tend to be highest for the materials filled with the untreated nanoparticles. Increased absorbed moisture content causes higher pre-breakdown currents for the nanocomposite materials, while for the reference unfilled material the pre-breakdown currents do not show such tendency. Generally it can be said that the repeatability in the measured data is higher for the nanocomposite materials in comparison to the unfilled host material, as was demonstrated by both dielectric spectroscopy and breakdown studies. / <p>QC 20130207</p>

<p>This work reports the chemical synthesis, characterisation and electrochemical application of titanium dioxide (TiO2) and iron oxide (Fe2O3) nanoparticles in the determination of phthalates. The other part of this work involved electrochemical polymerization of aniline doped with titanium and iron oxide nanoparticles for the sensor platform in the electrolytic determination of phthalates. The TiO2 and Fe2O3 nanoparticles were prepared by sol gel and hydrothermal methods respectively. Particle sizes of 20 nm (TiO2) and 50 nm (Fe2O3) were estimated from transmission electron microscopy (TEM) The other technical methods used in this study for the characterization of the TiO2 and iron oxide Fe2O3 NPs were SEM, XRD and UV- visible spectroscopy. Cyclic voltammetry, square wave voltammetry and electrochemical impedance spectroscopy (EIS) were used to study the electrochemical properties of the nanoparticles. These electrochemical studies of the nanoparticles were performed with a Fe2O3 or TiO2/nafion/glassy carbon membrane electrode in 0.1 M phosphate buffer (pH 7.0) and 0.1 M lithium perchlorate (pH 6.8) under an aerobic condition.</p>

Ultrathin film nanocomposites are becoming increasingly important for specialized performance of commercial coatings. Critical challenges for ultrathin film nanocomposites include their synthesis and characterization as well as their performance properties, including surface roughness, optical properties (haze, refractive index as examples), and mechanical properties. The objective of this work is to control the surface roughness of ultrathin film nanocomposites by changing the average particle size and the particle volume fraction (loading) of monomodal particle size distributions. This work evaluated one-layer and two-layer films for their surface properties. Monodispersed colloidal silica nanoparticles were incorporated into an acrylate-based monomer system as the model system. Ultrathin nanocomposites were prepared with three different size colloidal silica (13, 45, and 120 nm nominal diameters) at three different particle loadings (20, 40, and 50 vol. % inorganic solids). Silica particles were characterized using DLS and TEM. AFM was used to measure the root mean square roughness (Rq), ΔZ, and location-to-location uniformity of one-layer and two-layer nanocomposite coatings. Developing an understanding about the properties affected by the type and amount of particles used in a nanocomposite can be used as a tool with nanocharacterization techniques to quickly modify and synthesize desired ultrathin film coatings.

Les analogues du bleu de Prusse sont intéressants pour le stockage de l'information car ils présentent des propriétés de photo-commutation. Afin d'intégrer et d'exploiter ces propriétés photomagnétiques dans d'éventuelles applications, il est nécessaire de faire une étape de mise en forme. Cette dernière consiste à contrôler la taille, la forme ainsi que l'arrangement tridimensionnel des nanoparticules. Une stratégie consiste à élaborer des oxydes de silice nanostructurée par le procédé sol-gel. Une méthode a consisté faire précipiter les analogues du bleu de Prusse photomagnétiques dans la nanoporosité. Ainsi, il a fallu obtenir un monolithe ayant une unique organisation et non un mélange de phases. Il a été possible d'optimiser la méthode pour obtenir un monolithe hexagonal ayant des ions cobalt. Cette méthode a pu être étendue à différentes organisations : lamellaire, cubique, hexagonale, vermiculaire. Un traitement thermique permettant d'éliminer le copolymère afin de former le nanoréacteur. Une étude a permis de montrer que l'organisation etait conservée après un traitement thermique. Les ions cobalt subissaient une thermo hydrolyse durant le traitement thermique.Il a été possible de mettre en place une méthode d'imprégnation permettant d'obtenir différents nanocomposites CoFe et de contrôler la stœchiométrie des particules d'ABP confinées.Cette méthode a permis d'élaborer des nanocomposites CoFe sans cations alcalin et des nanocomposites CoFe contenant deux cations rubidium par maille. Les propriétés magnétiques ont permis de montrer l'effet de la mise en forme. De plus cette étude a permis de montrer que les propriétés de commuation sont concervées mêmes sur des nanoparticules de 5 nm.

Nanostructured materials are gaining an ongoing demand because of their exceptional chemical and physical properties. Due to complexities and costs of experimental studies at nanoscale, computer simulations are getting more attractive asexperimental alternatives. In this PhD work, we tried to use combination of atomistic simulations and continuum modeling for the evaluation of thermal conductivity and elastic stiffness of nanostructured materials. We used molecular dynamics simulations to probe and investigate the thermal and mechanical response of materials at nanoscale. The finite element and micromechanics methods that are on the basis of continuum mechanics theories were used to evaluate the bulk properties of materials. The predicted properties are then compared with existing experimental results.

Les nanotubes de carbone (NTC) ont été découverts en 1991 par Iijima. La réduction sélective de solutions solides d'oxydes (Al2-2xFe2xO3, Mg1-yMyAl2O4 et Mg1-zMzO avec M = Fe, Co, Ni ou alliages) par des mélanges H2-CH4 nous a permis d'obtenir des particules métalliques nanométriques à température élevée sur lesquelles la décomposition catalytique de CH4 permet la formation de NTC. Des poudres composites NTC-M-Oxyde sont ainsi préparées. L'étude des paramètres de synthèse est basée sur une caractérisation macroscopique s'appuyant sur des mesures de surfaces spécifiques, corrélée à des observations en microscopie électronique. Nous avons montré que les NTC se forment lors de la montée en température, à partir de 850°C. Les NTC préparés sont pour la plupart mono ou bi-feuillets et leurs diamètres internes sont compris entre 0,8 et 6 nm. Seules les particules suffisamment petites (£ 6 nm) conduisent à des NTC. Ceux-ci sont généralement regroupés en faisceaux dont le diamètre est inférieur à 50 nm et dont la longueur peut dépasser 100 μm. Des NTC isolés ont été obtenus par traitement acide de la poudre NTC-Co-MgO mais une partie des particules de cobalt subsiste, encapsulées dans des couches de graphène. L'oxydation ménagée de la poudre, préalablement au traitement acide, permet d'augmenter la teneur en carbone jusqu'à 94% at. Des composites massifs ont été préparés par frittage sous charge, et par extrusion à chaud dans le but d'aligner les NTC. L'extrusion est facilitée par la présence de métal, et plus encore par la présence conjointe de métal et de NTC. Ces derniers confèrent aux composites une conductivité électrique de l'ordre de 1 S.cm-1. L'effet d'alignement des NTC dans les échantillons extrudés est vérifié par une anisotropie de conductivité électrique. Les caractéristiques mécaniques (charge à la rupture et ténacité) des composites incluant des NTC sont comparables à celles des composites n'en contenant pas, bien que leur densification soit jusqu'à 10% plus faible. Mots-clés : nanotubes de carbone, nanocomposites, décomposition catalytique, solutions solides d'oxydes, extraction de nanotubes, extrusion à chaud.

Organic-inorganic nanostructured composites are nowadays integrated in the field of material science and technology. They are used as advanced materials directly or as precursors to novel composites with potential applications in optics, mechanics, energy, catalysis and medicine. Many properties of these complex materials depend on conformational rearrangements in their inherently dynamic organic parts. The focus of this thesis is on the study of the molecular mobility in ordered nanostructured composites and lyotropic mesophases and also on the development of relevant solid-state NMR methodologies. In this work, a number of new experimental approaches were proposed for dipolar NMR spectroscopy for characterizing molecular dynamics with atomic-level resolution in complex solids and liquids. A new acquisition scheme for two-dimensional dipolar spectroscopy has been developed in order to expand the spectral window in the indirect dimension while using limited radio-frequency power. Selective decoupling of spin-1 nuclei for sign-sensitive determination of the heteronuclear dipolar coupling has been described. A new dipolar recoupling technique for rotating samples has been developed to achieve high dipolar resolution in a wide range of dipolar coupling strength. The experimental techniques developed herein are capable of delivering detailed model-independent information on molecular motional parameters that can be directly compared in different composites and their bulk analogs. Solid-state NMR has been applied to study the local molecular dynamics of surfactant molecules in nanostructured organic-inorganic composites of different morphologies. On the basis of the experimental profiles of local order parameters, physical motional models for the confined surfactant molecules were put forward. In layered materials, a number of motional modes of surfactant molecules were observed depending on sample composition. These modes ranged from essentially immobilized rigid states to highly flexible and anisotropically tumbling states. In ordered hexagonal silica, highly dynamic conformationally disordered chains with restricted motion of the segments close to the head group have been found. The results presented in this thesis provide a step towards the comprehensive characterization of the molecular states and understanding the great variability of the molecular assemblies in advanced nanostructured organic−inorganic composite materials. / <p>QC 20150225</p>

The potential use of Resadiye/Tokat bentonite as a reinforcement in polypropylene (PP) and linear low density polyethylene (LLDPE) polymer matrix nanocomposites filler was investigated. At first, organoclays (OC) were prepared by cation exchange reaction (CER) between the raw bentonite (RB) and three quaternary ammonium salts with long alkyl tails (QA): hexadecyl trimethyl ammonium bromide [HMA] [Br], tetrabutyl ammonium tetrafluoroborate [TBA] [BF4], tetrakisdecyl ammonium bromide [TKA] [Br] and one quaternary phosphonium (QP) salt: tetrabutyl phosphonium tetrafluroborate [TBP] [BF4]. Characterization of resulting materials by XRD, TGA, FTIR and chemical analysis confirmed the formation of organoclays. Ternary composites of PP/organoclay/ maleic anhydride grafted polypropylene (MAPP) were prepared with two different grades of PPs in a co-rotating twin screw extruder. Composites prepared with these organoclays and PPs showed microcomposite formation. In the second part of the study, raw bentonite was purified by sedimentation, and characterization of purified bentonite (PB) by XRD, cation exchange capacity (CEC) measurement and chemical analysis (ICP) confirmed the success of purification method. PB was then modified with two QA`s: dimethyl dioctadecylammonium chloride [DMDA] [Cl], tetrakis decylammonium bromide [STKA] [Br] and one QP: tributyl hexadecyl phosphonium bromide [TBHP] [Br]. Organoclays from PB were used with the PP with lower viscosity, and ternary nanocomposites (PP/Organoclay2/MAPP5) were prepared in the extruder followed by batch mixing in an intensive batch mixer. Use of DMDA and TBHP OCs resulted in nanocomposite formation, while STKA resulted in microcomposite formation as observed by XRD and TEM. Young`s modulus and yield stress of the samples were enhanced through nanocomposite formation. In the last part of the study, ternary composites of LLDPE/Organoclay/ compatibilizer, a random terpolymer of ethylene, butyl acrylate and maleic anhydride (E-BA-MAH, Lotader&reg / 3210), were prepared by melt compounding in the batch mixer at two different clay concentrations (2 and 5 wt %) and fixed compatibilizer/organoclay ratio (&alpha / =2.5). A commercial organoclay, I34, was also used in LLDPE based nanocomposites to make a comparison. XRD and TEM analyses of the compounds prepared by DMDA and TBHP showed mixed nanocomposite morphologies consisting of partially intercalated and exfoliated layers. Young`s modulus and tensile strength of nanocomposites prepared with DMDA and TBHP showed generally higher values compared to those of neat LLDPE, while results were the highest in the composites prepared with commercial organoclay I34. Parallel disk rheometry was used as a supplementary technique to XRD, TEM and mechanical characterizations, and it was shown to be a sensitive tool in assessing the degree of dispersion of clay layers in the polymer matrix.