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Influence d'une contrainte mécanique sur le vieillissement d'alliages Fe-Cr / Influence of a mechanical load on the ageing of Fe-Cr alloysDahlström, Alexander 19 September 2019 (has links)
L’acier inoxydable est un alliage important pour le développement technique d’une société moderne; cela a été découvert au début du 20ème siècle. Cependant, leur système d'alliage de base, Fe-Cr, est affecté par une lacune de miscibilité à basse température (<600 °C) présent dans le diagramme de phases. Les alliages présentant une lacune de miscibilité dans leur diagramme de phase ont tendance à se décomposer. Ce phénomène également connu sous le nom de "fragilisation à 475 °C", est d’une importance technique, car la décomposition modifie les propriétés mécaniques de ces alliages; dans ce cas présente, par la perte de ductilité et de résistance aux chocs. La tendance à la décomposition augmente avec la diminution de la température, ce qui limite la température de service supérieure à environ 300 °C, limitant ainsi la durée de vie de ces alliages. Étant donné que la fragilisation peut provoquer une défaillance soudaine de ces alliages, cet aspect nuit à leur utilisation en tant que composants structurels dans les secteurs du transport et de l’énergie. La décomposition des alliages Fe-Cr pose un défi aux techniques de caractérisation traditionnelles, car les variations de composition se produisent à l'échelle nanométrique. Par conséquent, la sonde atomique tomographique de pointe a été utilisée pour étudier ces variations de composition à l'échelle atomique en 3D. La modélisation atomistique corrélative a été utilisée pour améliorer davantage la compréhension du processus de décomposition dans ces alliages ; ce modèle était basé sur la théorie de la fonction de densité atomique. Pour émuler la décomposition améliorée du matériau, causée par la température et/ou une charge externe, la décomposition dans ce projet est stimulée par une température de service supérieure à la normale. Dont la nécessité de connaître la limite exacte de la lacune de miscibilité. Ainsi, la nécessité d'évaluer la limite supérieure de température de cette décomposition dans le système Fe-Cr est née de résultats non concluants des analyses de la littérature existant. Par conséquent, un four de haute précision en combinaison avec une sonde atomique tomographique a été utilisé pour étudier la décomposition et l’agglomération dans le système Fe-Cr d’une manière plus précise que jamais. En outre, d’explorer en détail l’emplacement de la limite de la lacune de miscibilité. La décomposition de ces alliages au cours du vieillissement modifie les propriétés mécaniques. Ainsi, en raison de leur utilisation en tant que composants structurels, le comportement de décomposition dû au vieillissement a été étudié, ainsi que le vieillissement dû à la charge externe. Cette dernière situation se rencontre également dans des applications réelles pendant le service, émulées par le vieillissement dû à la pression en utilisant une simple force de traction. Afin d'examiner en détail l'effet de la pression externe, l'orientation du grain par rapport à la direction de traction a été prise en compte lors d'un simple vieillissement thermique et lors de l’application d’une force de traction continue. Ainsi, l'orientation cristallographique et les niveaux de charge ont été pris en compte pour leur effet sur le processus de décomposition/dégradation. / Stainless steel is an important alloy for the technical development of a modern society, they were discovered in the early 20th century. However, their base alloying system, Fe-Cr, is affected by a low temperature (<600°C) miscibility gap present in the phase diagram. Alloys with a miscibility gap in their phase diagram tend to decompose. This phenomenon is also known as the “475°C embrittlement”, it is of technical importance as decomposition alters the mechanical properties of these alloys, in this specific case, by loss of ductility and impact toughness. The tendency to decompose increases with decreasing temperature, restricting the upper service temperature to around 300°C and limiting the service lifetime of these alloys. Because embrittlement can cause sudden failure of these alloys, this phenomenon is detrimental to their use as structural components in transportation and energy industry. The decomposition of Fe-Cr alloys poses a challenge for traditional characterisation techniques, as composition variations occur at the nanoscale. Therefore, the state-of-the-art atom probe tomography have been utilised to study these composition variations at the atomic scale in 3D. Correlative atomistic modelling has been used to further enhance the understanding of the decomposition process in these alloys, this model was based on atomic density function theory. To emulate enhanced decomposition of the material, caused by temperature and/or an external load, decomposition in this work is stimulated by a higher than the normal service temperature. Hence, a need to know the exact limit of the miscibility gap. Thus, a need to evaluate the upper-temperature limit of this decomposition in the Fe-Cr system arose from inconclusive results in the literature. Hence, a high precision furnace in combination with atom probe was utilised to study decomposition and clustering in the Fe-Cr system more accurately than ever before. Furthermore, to explore in detail the location of the limit of the miscibility gap. The decomposition of these alloys during ageing alter the mechanical properties. Thus, due to their use as structural components, the decomposition behaviour during ageing was investigated, as well as ageing during external load. This last situation is also encountered in real applications during service, mimicked by stress-ageing using a simple tensile force. In order to in detail investigate the effect of the external stress, grain orientation with respect to the tensile direction was considered during simple thermal ageing, and during the constantly applied tensile force. Thus, crystallographic orientation and load levels were considered for their effect on the decomposition process.
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Numerical modeling of the surface and the bulk deformation in a small scale contact: application to the nanoindentation interpretation and to the micro-manipulationBerke, Peter 19 December 2008 (has links)
<p align='justify'>L’adaptation des surfaces pour des fonctions prédéterminées par le choix des matériaux métalliques ou des couches minces ayant des propriétés mécaniques avancées peut potentiellement permettre de réaliser des nouvelles applications à petites échelles. Concevoir de telles applications utilisant des nouveaux matériaux nécessite en premier lieu la connaissance des propriétés mécaniques des matériaux ciblés à l’échelle microscopique et nanoscopique. Une méthode souvent appliquée pour caractériser les matériaux à petites échelles est la nanoindentation, qui peut être vue comme une mesure de dureté à l’échelle nanoscopique.</p><p><p align='justify'>Ce travail présente une contribution relative à l'interprétation des résultats de la nanoindentation, qui fait intervenir un grand nombre de phénomènes physiques couplés à l'aide de simulations numériques. A cette fin une approche interdisciplinaire, adaptée aux phénomènes apparaissant à petites échelles, et située à l’intersection entre la physique, la mécanique et la science des matériaux a été utilisée. Des modèles numériques de la nanoindentation ont été conçus à l'échelle atomique (modèle discret) et à l'échelle des milieux continus (méthode des éléments finis), pour étudier le comportement du nickel pur. Ce matériau a été choisi pour ses propriétés mécaniques avancées, sa résistance à l'usure et sa bio-compatibilité, qui peuvent permettre des applications futures intéressantes à l'échelle nanoscopique, particulièrement dans le domaine biomédical. Des méthodes avancées de mécanique du solide ont été utilisées pour prendre en compte les grandes déformations locales du matériau (par la formulation corotationelle), et pour décrire les conditions de contact qui évoluent au cours de l'analyse dans le modèle à l'échelle des milieux continus (traitement des conditions de contact unilatérales et tangentielles par une forme de Lagrangien augmenté).</p><p><p align='justify'>L’application des modèles numériques a permis de contribuer à l’identification des phénomènes qui gouvernent la nanoindentation du nickel pur. Le comportement viscoplastique du nickel pur pendant nanoindentation a été identifié dans une étude expérimentale-numérique couplée, et l'effet cumulatif de la rugosité et du frottement sur la dispersion des résultats de la nanoindentation a été montré par une étude numérique (dont les résultats sont en accord avec des tendances expérimentales).</p> <p><p align='justify'>Par ailleurs, l’utilisation de l’outil numérique pour une autre application à petites échelles, la manipulation des objets par contact, a contribué à la compréhension de la variation de l’adhésion électrostatique pendant micromanipulation. La déformation plastique des aspérités de surface sur le bras de manipulateur (en nickel pur) a été identifiée comme une source potentielle d’augmentation importante de l'adhésion pendant la micromanipulation, qui peut potentiellement causer des problèmes de relâche et de précision de positionnement, observés expérimentalement.</p><p><p align='justify'>Les résultats présentés dans cette thèse montrent que des simulations numériques basées sur la physique du problème traité peuvent expliquer des tendances expérimentales et contribuer à la compréhension et l'interprétation d'essais couramment utilisé pour la caractérisation aux petites échelles. Le travail réalisé dans cette thèse s’inscrit dans un projet de recherche appelé "mini-micro-nano" (mµn), financé par la Communauté Française de Belgique dans le cadre de "l'Action de Recherche Concertée", convention 04/09-310.</p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished
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Phase Dynamics and Physico-Mechanical Behaviors of Electronic Materials: Atomistic Modeling and Theoretical StudiesHong Sun (9500594) 16 December 2020 (has links)
<p></p><p>Global demand for high performance, low cost, and eco-friendly
electronics is ever increasing. Ion/charge transport ability and mechanical
adaptability constitute two critical performance metrics of battery and
semiconductor materials, which are fundamentally correlated with their
structural dynamics under various operating conditions. It is imperative to
reach the mechanistic understanding of the structure-property relationships of
electronic materials to develop principles of materials design. Nevertheless,
the intricate atomic structure and elusive phase behaviors in the operation of
devices challenge direct experimental observations. Herein, we employ a
spectrum of modeling methods, including quantum chemistry, ab-initio modeling,
and molecular dynamics simulation, to systematically study the phase dynamics
and physico-mechanical behaviors of multiple electronic materials, ranging from
transition-metal cathodes, polymer derived ceramics anodes, to organic
semiconductor crystals. The multiscale atomistic modeling enriches the
fundamental understanding of the electro-chemo-mechanical behaviors of battery
materials, which provides insight on designing state-of-the-art energy
materials with high capacity and high structural stability. By leveraging the
genetic-algorithm refined molecular modeling and phase transformation theory,
we unveil the molecular mechanisms of thermo-, super- and ferroelastic
transition in organic semiconductor crystals, thus promoting new avenues of
adaptive organic electronics by molecular design. Furthermore, the proposed
computational methodologies and theoretical frameworks throughout the thesis
can find use in exploring the phase dynamics in a variety of environmentally
responsive electronics.</p><p></p>
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Modellering med differentialekvationer : Synliggörandet av olika delprocesser i matematisk modellering i kursplaner för blivande gymnasielärare i matematik / Modelling with differential equations : The visibility of different sub-processes in mathematical modelling in curricula for prospective upper secondary school teachers in mathematicsRexhaj, Behar, Teklu, Daniel January 2022 (has links)
Inom matematikdidaktik beskrivs matematisk modellering som en process bestående av olika delprocesser. Forskare inom området menar att ett holistiskt förhållningssätt behövs i undervisningen för att alla delprocesser i modelleringsprocessen ska kunna utvecklas. Syftet med denna studie är att undersöka kursplaners synliggörande (intended curriculum) av olika delprocesser vid matematisk modellering med differentialekvationer i svenska lärosätens ämneslärarprogram för gymnasiet med matematik som huvudämne. För att analysera kursplanerna används ett teoretiskt ramverk formulerat av Blomhøj & Jensen (2003). Resultatet visar stora skillnader i vilka delprocesser som synliggörs. Från nästan alla kursplaner som analyserades kunde man tydligt utläsa att i kursplanen synliggjordes delprocesser om matematisering av modelleringsproblem samt undersökning och lösning av uppkomna matematiska problem, medan andra delprocesser som speglar identifiering av ett verklighetsnära modelleringsproblem och tolkning av beräkningsresultatsynliggörs i mycket liten utsträckning. Delprocessen om analys av modellens giltighet synliggjordes i några enstaka kursplaner. En slutsats är att alla delprocesser inte synliggörs i kursplaner för matematikkurser i ämneslärarprogram för gymnasiet som behandlar modellering med differentialekvationer. Studien belyser behov av fortsatt forskning inom området, till exempel av det tillämpade genomförandet eller det uppnådda kursresultatet. / In mathematics education, mathematical modelling is described as a process consisting of different sub-processes. Researchers in the area believe that a holistic approach needs to be included in teaching where all sub-processes in the modelling process can be developed. The aim of this study is to investigate the visibility of different sub-processes in mathematical modelling in curricula (intended curriculum) with differential equations for Swedish teachers’programme with mathematics as core subject. To analyse the curricula, a theoretical framework formulated by Blomhøj & Jensen (2003) is used. The results show that there is a difference in the visibility of the sub-processes. From almost all curricula that were analysed, sub-processes on mathematization of modelling problems and investigation and solution of emerging mathematical problems could be clearly seen, while other sub-processes such as identification of a realistic modelling problem, interpretation and analysis of results could be seen to a lesser extent. The sub-process of analysing the validity of modelswas visible in a few curricula. Hence possible conclusions can be drawn, one is that curricula in modelling with differential equations for Swedish secondary education teacher programme in mathematics do not showcase all modellingsub-processes. The thesis highlights further need in studies of the implemented and attained curricula.
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Deformation of a Graphene Sheet Driven by Lattice Mismatch with a Supporting SubstrateStanek, Lucas James 20 November 2018 (has links)
No description available.
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Frictional Anisotropy of Graphene and Graphene Based MaterialsBarabanova, Liudmyla 10 June 2016 (has links)
No description available.
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Atomistic and molecular simulations of novel acid-base blend membranes for direct methanol fuel cellsMahajan, Chetan Vasant 04 February 2014 (has links)
One of the main challenges to transform highly useful Direct Methanol Fuel Cells (DMFC) into a commercially viable technology has been to develop a low cost polymer electrolyte membrane (PEM) with high proton conductivity, high stability and low methanol crossover under operating conditions desirably including high temperatures. Nafion, the widely used PEM, fails to meet all of these criteria simultaneously. Recently developed acid-base polymer blend membranes constitute a promising class of PEMs alternative to Nafion on above criteria. Even though some of these membranes produce better performance than Nafion, they still present numerous opportunities for maximizing high temperature proton conductivity and dimensional stability with concomitant minimization of methanol crossover. Our contribution embarks on the fundamental study of one such novel class of blend membranes viz., sulfonated poly (ether ether ketone) (SPEEK)(95 % by weight) blended with polysulfone tethered with base (5 % by weight) such as 2-aminobenzimidazole (ABIm), 5-amino-benzotriazole (BTraz) and 1H-perimidine (PImd), developed by Manthiram group at The University of Texas at Austin.
In this work, we report extensive all-atom classical as well as ab-initio molecular dynamics (MD) simulations of such water-methanol solvated blend membranes (as well as pure SPEEK and Nafion) the first time. Our approach consists of three steps: (1) Predict dynamical properties
such as diffusivities of water, methanol and proton in such membranes (2) Validate against experiments (3) Develop understanding on the
interplay between basic chemistry, structure and properties, the knowledge that can potentially be used to develop better candidate membranes.
In particular, we elucidate the impact of simple, fundamental physiochemical features of the polymeric membranes such as hydrophilicity,
hydrophobicity, structure or the size of the base on the structural manifestations on the bigger scale such as nanophase segregation, hydrogen bonding or pore sizes, which ultimately affect the permeant transport through such systems. / text
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Development of scale-bridging methodologies and algorithms founded on the outcome of detailed atomistic simulations for the reliable prediction of the viscoelastic properties of polymer melts / Ανάπτυξη μεθοδολογιών και αλγορίθμων πρόβλεψης της ρεολογίας πολυμερικών τηγμάτων βασιζόμενοι στα αποτελέσματα λεπτομερών ατομιστικών προσομοιώσεωνΣτεφάνου, Παύλος 11 August 2011 (has links)
In this thesis we design and develop algorithms for predicting the rheological behavior of polymer melts based on the results of detailed atomistic simulations and guided by theories of the Dynamics of Polymers and fundamental Principles of Science of the Non-Equilibrium Thermodynamics. More specifically:
1) We propose a new rheological constitutive model for the time evolution of the tensor conformation tensor C of chains in a polymer melt (and hence the stress tensor τ) using the generalized bracket formalism of Beris and Edwards. The new constitutive model includes terms that describe a whole range of phenomena and are successfully used to describe the rheological properties of commercial polyethylene resins.
2) We developed a new methodology that allows direct connection of the results of atomistic simulations with molecular reptation theory for entangled polymers. The final result of the methodology is the calculation of the function ψ(s,t) which expresses the probability that the segment s along the contour of the primitive path remain in the original tube after time t.
3) We extended the Rouse theory for systems without polymer chain ends, as the polymer rings. While there have been previous theoretical work, a comprehensive analysis of the Rouse model of cyclic polymers was still lacking; here we develop the theory in its entirety. / Στα πλαίσια της παρούσας διατριβής σχεδιάσαμε και αναπτύξαμε αλγορίθμους πρόβλεψης της ρεολογικής συμπεριφοράς πολυμερικών τηγμάτων βασιζόμενοι στα αποτελέσματα λεπτομερών ατομιστικών προσομοιώσεων, καθοδηγούμενοι όμως από Θεωρίες της Δυναμικής των Πολυμερών αλλά και από θεμελιώδεις αρχές της Επιστήμης της Θερμοδυναμικής Εκτός Ισορροπίας. Πιο συγκεκριμένα:
1) Προτείνουμε αρχικά ένα νέο ρεολογικό καταστατικό μοντέλο για τη χρονική εξέλιξη του τανυστή διαμορφώσεων C των αλυσίδων σε ένα πολυμερικό τήγμα (και κατ’ επέκταση για τον τανυστή των τάσεων τ) κάνοντας χρήση του φορμαλισμού των γενικευμένων αγκυλών των Beris και Edwards. Το νέο καταστατικό μοντέλο περιλαμβάνει όρους που περιγράφουν ένα ολόκληρο φάσμα φαινομένων και χρησιμοποιήθηκε με επιτυχία για την περιγραφή των ρεολογικών ιδιοτήτων εμπορικών ρητινών πολυαιθυλενίου.
2) Αναπτύξαμε μια καινούργια μεθοδολογία που επιτρέπει την άμεση σύνδεση των αποτελεσμάτων των ατομιστικών προσομοιώσεων με τη μοριακή θεωρία του ερπυσμού για διαπλεγμένα πολυμερή. Το τελικό αποτέλεσμα της μεθοδολογίας είναι ο υπολογισμός της συνάρτησης ψ(s,t) που εκφράζει την πιθανότητα το σημείο s κατά μήκος του περιγράμματος του πρωτογενούς δρόμου των αλυσίδων να παραμένει στον αρχικό σωλήνα μετά από χρόνο t.
Επεκτείναμε τη θεωρία Rouse και για συστήματα πολυμερικών αλυσίδων δίχως άκρα, όπως αυτά των πολυμερικών δακτυλίων. Παρότι στίγματα της θεωρίας είχαν παρουσιαστεί και σε προηγούμενες εργασίες από άλλους ερευνητές, στην παρούσα διατριβή αναπτύξαμε τη θεωρία στην ολότητά της.
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Σχέσεις δομής και ιξωδοελαστικών, μηχανικών και συγκολλητικών ιδιοτήτων πολυακρυλικών σε στερεά υποστρώματα μέσω ατομιστικών προσομοιώσεων / Structure-property (viscoelastic, mechanical, and adhesive) relationships in polyacrylic adhesives through atomistic simulationsΑναστασίου, Αλέξανδρος 27 August 2014 (has links)
The present Doctoral Thesis focuses on the investigation, characterization and influence of polyacrylic materials in different scientific and technological disciplines via a detailed computer simulation using the Molecular Dynamics (MD) technique, in conjunction with the very accurate, all-atom Dreiding force-field. The main research concepts and objectives are discussed and analyzed in three separate parts.
In the first part, atomistic configurations of two model pressure-sensitive acrylic adhesives (PSAs), the atactic homopolymer poly(n-BA) [poly(n-butyl acrylate)] and the atactic copolymer poly(n-BA-co-AA) [poly(n-butyl acrylate-co-acrylic acid)] in the bulk phase or confined between two selected substrates, glassy silica (SiO2) and metallic α-ferrite (α-Fe), were built and simulated by MD in the NPT statistical ensemble. First, an equilibration cycle consisting of temperature annealings and coolings was followed, in order to generate well-equilibrated configurations of the PSA systems. Detailed results from the atomistic simulations are presented concerning their volumetric behavior, glass transition temperature, conformational, structural, viscoelastic and dynamic properties. Particular emphasis was given to the analysis and characterization of the hydrogen bonds that form in the poly(n-BA-co-AA) system. By analyzing the MD trajectories, poly(n-BA-co-AA) was found to exhibit a higher density than poly(n-BA) by about 7% at all temperatures, to be characterized by smaller-size chains for a given molecular weight (MW), to exhibit significantly slower terminal and segmental dynamics properties, and to be characterized by a glass transition temperature that was approximately 40% higher than that of poly(n-BA). We also examined the type and degree of adsorption of the two acrylic systems on the selected substrates by analyzing the MD results for the local mass density as a function of distance from the solid plane and the distribution of adsorbed chain segments in train, loop, and tail conformations, and by computing the work of adhesion at the two substrates. The results revealed a stronger adsorption for both acrylics on the SiO2 surface due to highly attractive interactions between polymer molecules and substrate atoms, and as a consequence a higher value for the work of adhesion compared to that on the α-Fe surface. Furthermore, we have developed a generalized non-equilibrium molecular dynamics (NEMD) algorithm to simulate the mechanical response of the two adhesives under a uniaxial stretching deformation.
In the second part of the Thesis, results have been obtained from a hierarchical simulation methodology that led to the prediction of the thermodynamic, conformational, structural, dynamic and mechanical properties of two polymer nanocomposites based on syndiotactic poly(methyl methacrylate) or sPMMA. The first was reinforced with uniformly dispersed graphene sheets and the second with fullerene particles. How graphene functionalization affects the elastic constants of the resulting nanocomposite has also been examined. The phase behavior of the nanocomposite (in particular as we varied the relative size between the sPMMA chains and the diameter of fullerene molecules) has also been studied as a function of fullerene volume fraction. The simulation strategy entailed three steps: 1) Generation of an initial structure, which was then 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. 2) Gradual cooling of selected configurations down to room temperature to obtain a good number of structures representative of the glassy phase of the polymer nanocomposite. 3) Molecular mechanics (MM) calculations of its mechanical properties following the method originally proposed by Theodorou and Suter. By analyzing the results under constant temperature and pressure, all nanocomposite systems were found to exhibit slower terminal and segmental relaxation dynamics than the pure polymer matrices. The addition of a small fraction of graphene sheets led in all cases to the enhancement of the elastic constants; this was significantly more pronounced in the case of functionalized graphene sheets. We further mention that, for all polymer/fullerene nanocomposites addressed here, no phase separation or variation of polymer chain dimensions was observed as a function of fullerene size and/or fullerene volume fraction.
In the third part of the Thesis, and motivated by the use of acrylic polymers for the design of membranes with aligned carbon nanotubes (CNTs) for several separation technologies (such as water desalination and wastewater treatment), we report results from a detailed computer simulation study for the nano-sorption and mobility of four different small molecules (water, tyrosol, vanillic acid, and p-coumaric acid) inside smooth single-wall CNTs (SWCNTs). Most of the results have been obtained with the molecular dynamics (MD) method, but especially for the most narrow of the CNTs considered, the results for water molecule were further confirmed through an additional Grand Canonical (μVT) Monte Carlo (GCMC) simulation using a value for the water chemical potential μ pre-computed with the particle deletion method. Issues addressed in the Thesis include molecular packing and ordering inside the nanotube for the four molecules, average number of sorbed molecules per unit length of the tube, and mean residence time and effective axial diffusivities, all as a function of tube diameter and tube length. In all cases, a strong dependence of the results on carbon nanotube diameter was observed, especially in the way the different molecules are packed and organized inside the CNT. For water for which predictions of properties such as local structure and packing were computed with both methods (MD and GCMC), the two sets of results were found to be fully self-consistent for all types of SWCNTs considered. Water diffusivity inside the CNT (although, strongly dependent on the CNT diameter) was computed with two different methods, both of which gave identical results. For large enough CNT diameters (larger than about 13 Å), this was found to be higher than the corresponding experimental value in the bulk by about 55%. Surprisingly enough, for the rest of the (phenolic) molecules simulated in this Thesis, the simulations revealed no signs of mobility inside nanotubes with a diameter smaller than the (20, 20) tube. This has been attributed to strong phenyl-phenyl attractive interactions, also to favorable interactions of these molecules with the CNT walls, which cause them to form highly ordered, very stable structures inside the nanotube, especially under strong confinement. The interaction, in particular, of the methyl group (present in tyrosol, vanillic acid, and p-coumaric acid) with the CNT walls seems to play a key role in all these compounds causing them to remain practically immobile inside nanotubes characterized by diameters smaller than about 26 Å. It was only for larger-diameter CNTs that tyrosol, vanillic acid, and p-coumaric acid were observed to demonstrate appreciable mobility. / Η παρούσα Διδακτορική Διατριβή εστιάζει στη μελέτη της σχέσης μεταξύ δομής και μακροσκοπικών φυσικών ιδιοτήτων υλικών από πολυακρυλικά μέσω μίας λεπτομερούς προσομοίωσης στον υπολογιστή με τη μέθοδο της Μοριακής Δυναμικής (ΜΔ), σε συνδυασμό με ένα πολύ επακριβές πεδίο δυνάμεων (το Dreiding) σε ατομιστική λεπτομέρεια. Οι κύριες ερευνητικές έννοιες καθώς και οι στόχοι συζητιούνται και αναλύονται σε τρία ξεχωριστά μέρη. Στο πρώτο μέρος, ατομιστικές απεικονίσεις δύο προτύπων πίεσο-ευαίσθητων συγκολλητικών υλικών (acrylic pressure sensitive adhesives ή PSAs), του ατακτικού πολυ-βουτυλικού-ακρυλικού εστέρα (poly(n-BA)) και του συμπολυμερούς του με ακρυλικό οξύ (poly(n-BA-co-AA)), τόσο μακριά όσο και κοντά σε υποστρώματα σίλικας (SiO2) και α-φερρίτη (α-Fe), μελετήθηκαν στη βάση ενός φάσματος ιδιοτήτων (θερμοδυναμικές, δομικές, ιξωδοελαστικές, δυναμικές, και συγκολλητικές), όπως και η μηχανική τους απόκριση υπό συνθήκες μονοαξονικής εκτατικής παραμόρφωσης. Στο δεύτερο μέρος παρουσιάζονται τα αποτελέσματα που εξήχθησαν από μία ιεραρχική μεθοδολογία προσομοίωσης που οδήγησε στην πρόβλεψη της φασικής συμπεριφοράς και των μηχανικών ιδιοτήτων νανοσύνθετων πολυμερικών υλικών (polymer nanocomposites ή PNCs) βασισμένων στο συνδιοτατκτικό πολυ-μεθακρυλικό μεθυλεστέρα (syndiotactic poly(methyl methacrylate) ή sPMMA), ενισχυμένο με ομοιόμορφα διεσπαρμένα φύλλα γραφενίου (graphene sheets) ή σωματίδια φουλερενίου (fullerene particles). Στο τρίτο μέρος, υποκινούμενοι από τη χρήση των ακρυλικών πολυμερών στο σχεδιασμό μεμβρανών με ενσωματωμένους ευθυγραμμισμένους νανοσωλήνες άνθρακα (ΝΑ, carbon nanotubes ή CNTs) σε διάφορες τεχνολογίες διαχωρισμού μορίων (με έμφαση στον καθαρισμό του νερού), παρουσιάζουμε αποτελέσματα από προσομοιώσεις, για τη νανο-ρόφηση και την κινητικότητα τεσσάρων διαφορετικών μικρών μορίων (water, tyrosol, vanilic acid, και p-coumaric acid) στο εσωτερικό λείων μονο-στρωματικών ΝΑ (single-wall CNTs ή SWCNTs). Τα θέματα που εξετάζονται περιλαμβάνουν τη μοριακή διευθέτηση και τη διάταξη στο εσωτερικό Ν.Α. των τεσσάρων μορίων, το μέσο χρόνο παραμονής τους, καθώς και τους αξονικούς συντελεστές διάχυσής του, συναρτήσει της διαμέτρου και του μήκους των ΝΑ.
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