Dissertations / Theses on the topic 'Glass transition temperature'
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1
Berglund, Peter. "The glass transition in high-temperature superconductors." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-26388.
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In high-temperature superconductors a large region of the magnetic phase diagram is occupied by a vortex phase. This vortex phase can be divided into two regions. At lower temperatures the vortices are in a truly superconducting solid phase. At higher temperatures the solid changes to a dissipative vortex liquid. The transition between the two phases depends of the disorder in the material. If there is no or low disorder the transition is a first order transition but if there are a lot of disorder the vortex solid is called a vortex glass and the transition is a second order transition. To describe this theoretically there are two kinds of models. First introduced was the so called vortex glass model with its characteristics of diverging time and length scales. Later was thevortex molasses scenario introduced, where only a diverging time scale can be observed. The task of this thesis is to try to distinguish between the two kinds of models. This was carried out by sensitive R(T) measurements. The experiment was based on single crystals of YBa2Cu3O7-(YBCO). An unambiguous result could not be obtained, further experiments would have to be conducted to make definite conclusions.
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Guan, Qing. "Sodium diffusion in soda-lime-silicate glass around the glass transition temperature /." The Ohio State University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487687115926219.
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Zhang, Yuwei. "A study of the measurement of glass transition temperature." Thesis, University of Bristol, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.508077.
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Hsu, Chuan-liang. "Influence of cooling rate on glass transition temperature and starch retrogradation during low temperature storage /." free to MU campus, to others for purchase, 1998. http://wwwlib.umi.com/cr/mo/fullcit?p9924889.
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Juang, Yi-Je. "Polymer professing and rheological analysis near the glass transition temperature." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1302020366.
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Juang, Yi-Je. "Polymer processing and rheological analysis near the glass transition temperature /." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486398195327065.
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Arab, B., A. Shokuhfar, and S. Ebrahimi-Nejad. "Glass Transition Temperature of Cross-Linked Epoxy Polymers: a Molecular Dynamics Study." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35102.
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Recently, epoxy polymers have been used in different applications and research fields due to their superior properties. In this study, the classical molecular dynamics (MD) was used to simulate formation of
the epoxy polymer from cross linking of the EPON 828 with DETA curing agent, and calculate the glass
transition temperature (Tg) of the material. A series of MD simulations were independently carried out on
the cross-linked epoxy polymer in a range of temperatures from 600 K down to 250 K, and the density of
the materials was calculated at the end of each run. Through the linear fitting between temperature and
density above and below the glass transition temperature, Tg was estimated. The glass transition temperature of the pure DGEBA were also estimated through the same procedure and compared with those of the
cross-linked polymer. Molecular simulations revealed significant increase in Tg of the cross-linked epoxy
polymer as a result of newly created covalent bonds between individual chains.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35102
8
Singh, Lovejeet. "Effect of Nanoscale Confinement on the Physical Properties of Polymer Thin Films." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4822.
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The behavior of polymeric systems confined into thin films is a situation that has numerous practical consequences. One particular application in which the properties of thin polymer films is becoming crucially important is in the design, formulation, and processing of photoresists for semiconductor microlithography. As devices continue to be scaled down into the nano-regime, the microelectronics industry will ultimately rely upon a molecular understanding of materials for process development. The majority of these devices are now confined in planar geometries; thus, thin films have played an ever-increasing role in manufacturing of modern electronic devices. This movement towards thinner resist films creates larger surface to volume ratios, and hence thin films can exhibit thermodynamic, structural, and dynamic properties that are different from those of the bulk material. It is thus extremely important to understand the properties of polymers when confined in such geometries for various applications including resists for lithographic patterning. In present work, the influence of a variety of factors including film thickness, molecular weight, and substrate interactions on the polymer thin film physical properties such as the glass transition temperature, coefficient of thermal expansion, dissolution rate, and diffusion coefficient was studied in detail using a combination of experimental characterization and molecular modeling simulation techniques.
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Mlynarczyk, Paul John. "The nature and determination of the dynamic glass transition temperature in polymeric liquids." Kansas State University, 2014. http://hdl.handle.net/2097/17782.
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Master of ScienceDepartment of Chemical Engineering
Jennifer L. Anthony
A polymer has drastically different physical properties above versus below some characteristic temperature. For this reason, the precise identification of this glass transition temperature, T[subscript]g, is critical in evaluating product feasibility for a given application. The objective of this report is to review the behavior of polymers near their T[subscript]g and assess the capability of predicting T[subscript]g using theoretical and empirical models. It was determined that all polymers begin to undergo structural relaxation at various temperatures both nearly above and below T[subscript]g, and that practical assessment of a single consistent T[subscript]g is successfully performed through consideration of only immediate thermal history and thermodynamic properties. It was found that the best quantitative structure-property relationship (QSPR) models accurately predict T[subscript]g of polymers of theoretically infinite chain length with an average error of less than 20 K or about 6%, while T[subscript]g prediction for shorter polymers must be done by supplementing these T[subscript]g (∞) values with configurational entropy or molecular weight relational models. These latter models were found to be reliable only for polymers of molecular weight greater than about 2,000 g/mol and possessing a T[subscript]g (∞) of less than about 400 K.
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Bouscarrat, David. "Time-dependent damage in woven-ply thermoplastic composites above glass transition temperature Influence of time-dependent phenomena on translaminar fracture of woven-ply C/PPS laminates above the glass transition temperature." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMIR29.
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Dans les composites associant matrice organique et renfort fibreux, le couplage entre comportements visqueux (viscoélasticité, viscoplasticité) et mécanismes d’endommagement est très peu étudié à l’échelle mésoscopique et se limite principalement à des analyses post-mortem. Pour des applications aéronautiques à haute température (e.g., nacelle de moteur d’avion), la problématique est encore plus complexe. Notamment au sein de stratifiés à matrice thermoplastique haute performance PPS renforcés par des tissus de fibres de carbone. Ces matériaux sont caractérisés par des zones riches en matrice dont les comportements visqueux sont amplifiés pour des températures d’utilisation en service (i.e., 120°C) supérieures à la température de transition vitreuse de la matrice (environ 95°C). La question fondamentale qui se pose alors est de comprendre comment mettre en évidence et quantifier l’endommagement d’origine visqueuse lorsque le comportement de stratifiés C/PPS est piloté par la réponse mécanique de la matrice. Pour apporter des réponses à cette problématique, on peut évaluer : (1) l’influence de la viscosité de la matrice sur le comportement en rupture translaminaire - (2) le visco-endommagement lors de chargements de type fluage-recouvrement. Ces deux axes d’étude reposent notamment sur la mise au point de protocoles expérimentaux adaptés à des essais mécaniques à haute température. Ainsi, l’originalité de ces travaux est de combiner différentes techniques complémentaires (émission acoustique, réplique de bords, analyse fractographique, tomographie) qui permettent une analyse in-situ en temps réel des mécanismes d’endommagement qui coexistent et inter-agissent lors des différentes phases du chargement. En utilisant le protocole mis au point dans des conditions de température supérieure à la Tg du matériau, ces techniques apportent des informations pour quantifier et dissocier les différents comportements matériaux (viscoélasticité, viscoplasticité, endommagements) ainsi que des effets structures (rotation des fibres). Des analyses d’images basées sur des algorithmes de dilatation/érosion implémentées dans Matlab permettent d’évaluer la densité de fissuration (intra- et inter-torons) surfacique à partir des répliques de bords. A l’échelle macroscopique, la réponse thermomécanique du C/PPS est peu influencée par les comportements visqueux du C/PSS que ce soit pour des stratifiés quasi-isotrope (comportement majoritairement piloté par les fibres à 0°) ou à plis orientés (comportement majoritairement piloté par la matrice PPS). Enfin, la rupture translaminaire ductile est caractérisée par l’évolution de l’énergie acoustique cumulée en fonction du taux de restitution d’énergie. L’instabilité de la rupture translaminaire ne permet pas d’évaluer l’influence des effets visqueux sur la ténacité en mode I du matériau à l’initiation. Aux échelles micro- et mésoscopiques, les résultats obtenus montrent clairement le visco-endommagement au sein de stratifiés C/PPS à plis orientés sollicités en fluage à T > Tg. En mettant en œuvre ce protocole, la pertinence/complémentarité démontrées de l’émission acoustique associée à la quantification de la densité de fissuration permettent d’envisager l’étude du couplage entre effets visqueux et endommagement au sein de stratifiés C/PPS soumis à des chargements à haute température. Cette problématique est essentielle du point de vue de la durabilité des structures composites dans un environnement moteurIn fiber-reinforced polymer matrix composite materials, the coupling between viscous behaviour (viscoelasticity, viscoplasticity) and damage mechanisms is very little studied at the mesoscopic scale and is mainly limited to port-mortem analyses. For high-temperature aeronautical applications (e.g., aircraft engine nacelle), the problem is even more complex within high performance thermoplastic matrix laminates PPS (Polyphenylene Sulfide) reinforced with carbon fiber fabrics. Indeed, these materials are characterized by matrix-rich zones whose viscous behaviors are exacerbated for service temperatures (i.e., 120°C) higher than the matrix glass transition temperature (about 95°C). It is therfore necessary to develop specific experimental procedures to highlight and quantify the viscous damage when the behaviour of C/PPS laminates is driven by the mechanical response of the matrix. In order to provide answers to this problem, one can evaluate : (1) the influence of the matrix viscosity on the translaminar fracture behaviour - (2) the time-dependent damage during creep-type loading. These two lines of study are based on the development of experimental protocols adapted to high temperature mechanical testing. Thus, the originality of this work is to combine different complementary techniques (acoustic emission, edge replication, fractographic analysis, tomography) which allow in-situ and in real time analyses of the damage mechanisms that coexist and interact during the different loading phases. Using the protocol developed under conditions of temperature higher than the Tg of the material, these techniques provide information to quantify and dissociate the different material behaviours (viscoelasticity, viscoplasticity, damage) as well as structural effects (fibre rotation). Image analyses based on dilatation/erosion algorithms implemented in Matlab allow the evaluation of the surface cracking density (intra- and inter-strand) from edge replicas. On a macroscopic scale, the thermomechanical response of C/PPS is little influenced by the viscous behaviour of C/PSS, whether for quasi-isotropic laminates (behaviour mainly driven by 0°fibres) or with oriented plies (behaviour mainly driven by the PPS matrix). Finally, the ductile translaminar fracture is characterized by the evolution of the cumulative acoustic energy as a function of the energy restitution rate. The instability of the translaminar fracture does not allow the quantification of the influence of viscous effects on the mode I toughness of the material at initiation. At micro and mesoscopic scales, the results obtained clearly show time-dependent damage within oriented plies C/PPS laminates subjected to creep loadings at T > Tg. By implementing this protocol, the demonstrated relevance/complementarity of the acoustic emission associated with the quantification of the cracking density allows the study of the coupling between viscous effects and damage within C/PPS laminates subjected to high temperature loading. This problem is essential from the point of view of the durability of composite structures in an engine environment
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Espinosa, Arronte Beatriz. "Resistivity and the solid-to-liquid transition in high-temperature superconductors." Doctoral thesis, KTH, Microelectronics and Applied Physics, MAP, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4251.
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In high-temperature superconductors a large region of the magnetic phase diagram is occupied by a vortex phase that displays a number of exciting phenomena. At low temperatures, vortices form a truly superconducting solid phase which at high temperatures turns into a dissipative vortex liquid. The character of the transition between these two phases depends on the amount and type of disorder present in the system. For weak point disorder the vortex solid-to-liquid transition is a first-order melting. In the presence of strong point disorder the solid is thought to be a vortex-glass and the transition into the liquid is instead of second order. When the disorder is correlated, like twin boundaries or artificially introduced columnar defects, the transition is also second order, but has essentially different properties. In this work, the transition between the solid and liquid phases of the vortex state has been studied by resistive transport measurements in mainly YBa2Cu3O7-[delta](YBCO) single crystals with different types of disorder.
The vortex-glass transition has been investigated in an extended model for the vortex-liquid resistivity close to the transition that takes into account both the temperature and magnetic field dependence of the transition line. The resistivity of samples with different properties was measured with various contact configurations at several magnetic fields and analyzed within this model. For each sample, attempts were made to scale the transition curves to one curve according to a suitable scaling variable predicted by the model. Good scaling was found in a number of different situations. The influence of increasing anisotropy and angular dependence of the magnetic field in the model were also considered.
The vortex solid-to-liquid transition was also studied in heavy-ion irradiated YBCO single crystals. The ions create columnar defects in the sample that act as correlated disorder. A magnetic field was applied at a tilt angle with respect to the direction of the columns. At the transition the resistance disappears as a power law with different exponents in the three orthogonal directions considered. This provides evidence for a new type of critical behavior with fully anisotropic critical scaling properties not previously found in any physical system.
The effect on the vortex solid-to-liquid transition of high magnetic fields applied parallel to the superconducting layers of underdoped YBCO single crystals was also studied. Some novel features were observed: a sharp kink appearing close to Tc at high magnetic fields and a triple dip in the angular dependence of the resistivity close to B||ab in some regions of the phase diagram.
I högtemperatursupraledare består en stor del av det magnetiska fasdiagrammet av en vortexfas som uppvisar ett flertal spännande fenomen. Vid låga temperaturer bildar vortexarna en fast vortexfas utan elektriskt motstånd. Vid högre temperatur övergår denna fas till en dissipativ vortexvätska. Egenskaperna hos denna fasövergång beror på oordningen i form av defekter. Vid svag punktoordning är fasomvandlingen mellan det fasta och flytande vortextillståndet en första ordningens smältövergång. Vid stark punktoordning anses den fasta fasen vara ett vortexglas och övergången till vortexvätskan är istället av andra ordningen. När oordningen är korrelerad, som för tvillinggränser eller artificiellt skapade kolumndefekter, är övergången också av andra ordningen men med väsentligt annorlunda egenskaper. I detta arbete har övergången mellan det fasta och det flytande vortextillståndet studerats med resistiva transportmätningar i framförallt enkristaller av YBa2Cu3O7-[delta] (YBCO) med olika typer av oordning.
Vortexglasövergången har undersökts i en utvidgad modell för resistansen i vortexvätskan nära fasövergången där hänsyn tas till såväl temperatur- som fältberoendet. Resistansen hos prover med olika egenskaper mättes i varierande magnetfält och i flera kontaktkonfigurationer och analyserades inom denna modell. Övergångskurvorna skalades till en kurva med en skalningsvariabel som givits av modellen. God skalning uppnåddes i flera olika fall. Effekten av ökande anisotropi och vinkelberoendet i modellen undersöktes också.
Vortexövergången mellan det fasta och det flytande vortextillståndet undersöktes även i enkristaller av YBCO bestrålade med tunga joner. Jonerna skapade kolumndefekter som fungerar som korrelerad oordning. Vinkeln mellan pålagt magnetfält och dessa kolumndefekter varierades. Vid fasövergången avtar resistansen som en potenslag med olika exponenter i de tre undersökta ortogonala riktningarna. Detta ger experimentell belägg för en ny typ av kritiskt beteende med fullständigt anisotropa kritiska skalningsegenskaper.
Egenskaparna hos på vortexövergången mellan fast och flytande fas vid höga magnetfält parallella med de supraledande lagren hos underdopade YBCO enkristaller undersöktes också. Några nya effekter observerades: en skarp knyck uppstod nära Tc vid höga magnetfält och en tredubbel dipp i den vinkelberoende resistiviteten nära B||ab i några regioner av fasdiagrammet.
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Chandrasekaran, Gurucharan. "Material Characterization and Modeling of Strain Induced Crystallization in PET above the Glass Transition Temperature." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1218053145.
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Lu, Xiaolin. "The study of polymers in geometrically confined states by the thermal analysis, the spectroscopic study, and the morphological investigation /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?CENG%202004%20LU.
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Le, Baut Nicolas. "Physical and adhesive properties of some materials made by "click" chemistry." Access electronically, 2005. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20060712.161329/index.html.
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Gao, Yongxiang. "Direct observation of correlated motions in colloidal gels and glasses." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=115677.
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Dynamical heterogeneity (DH) has been observed in many systems approaching the glass or jamming transition. Whether DH has a structural origin is under heated debate. To provide a deeper understanding, in this thesis I investigate the microscopic dynamics in weakly attractive colloidal systems by confocal fluorescence microscopy. The van Hove density-density correlation function is applied to our systems. Separable fast and slow populations emerge in the self part (svH), while the distinct part shows a strong signature of DH close to the gel transition. At intermediate time, svH shows a purely exponential tail, mainly arising from the fast population. I show that this broad tail is a direct consequence of the occurrence of rare large jumps that are statistically distributed. The slow population tends to form a space-spanning backbone, and its mean squared displacement close to the gel transition exhibits a plateau, whose height is consistent with the range of attraction, suggesting a bonding mechanism for the dynamical arrest. I further examine various quantities characterizing local structure and local dynamics and a strong correlation is identified between them. Subsequently, I develop order parameters for quantifying amorphous structure and apply them to our systems. I find that attractive colloidal systems exhibit higher order under higher attraction tension, while hard spheres become more ordered under higher compression. Finally, I investigate the effect of the range of attraction on the structure and dynamics of attractive colloidal systems. I observe that the system with shorter range of attraction forms a denser and more heterogeneous structure. Meanwhile, I observe an even stronger dynamical heterogeneity. These observations provide further evidence of a connection between structural heterogeneity and dynamical heterogeneity in these systems, providing guidance for a theoretical description of the dynamical arrest as well as the relaxation mechanisms upon gelation and its relation to solidification in glasses.In order to do all of this, I first implemented full 3D subpixel resolution localization of particles and improved particle tracking algorithms tailored for the sorts of heterogenous dynamics these systems exhibit, that otherwise confounds existing methods such that the very relaxation mechanisms would be missed. This allows us to obtain unprecedented precision in positions of all of the particles and complete tracking, both of which are essential for correctly determining system properties that depend on measured particle dynamics.
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Dupaix, Rebecca B. (Rebecca Brown) 1976. "Temperature and rate dependent finite strain behavior of poly(ethylene terephthalate) and poly(ethylene terephthalate)-glycol above the glass transition temperature." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/7972.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.Includes bibliographical references (p. 333-348).
Poly(ethylene terephthalate) is widely used for consumer products such as drawn fibers, stretched films, and soda bottles. Much of its commercial success lies in the fact that it crystallizes at large strains during warm deformation processing. The imparted crystallinity increases its stiffness and strength, improves its dimensional stability, and increases its density. The crystallization process and the stress-strain behavior above the glass transition depend strongly on temperature, strain rate, strain magnitude, and strain state. A robust constitutive model to accurately account for this stress-strain behavior in the processing regime is highly desirable in order to predict and computationally design warm deformation processes to achieve desired end product geometries and properties. This thesis aims to better understand the material behavior above the glass transition temperature in the processing regime. It examines the strain rate, strain state, and temperature dependent mechanical behavior of two polymers: PET and PETG, an amorphous non-crystallizing copolymer of PET, in order to isolate the effects of crystallization on the stress-strain behavior. Experiments over a wide range of temperatures and strain rates were performed in uniaxial and plane strain compression. A constitutive model of the observed rate and temperature dependent stress-strain behavior was then developed. The model represents the material's resistance to deformation with two parallel elements: an intermolecular resistance to flow and a resistance due to molecular network interactions.
(cont.) The model predicts the temperature and rate dependence of many stress-strain features of PET and PETG very well, including the initial modulus, flow stress, initial hardening modulus, and dramatic strain hardening. The modeling results indicate that the large strain hardening behavior of both materials can only be captured by including a critical orientation parameter to halt the molecular relaxation process once the network achieves a specific level of molecular orientation. This suggests that much of the strain hardening in PET is due to molecular orientation and not to strain-induced crystallization. An example blow molding process is simulated to demonstrate the industrial applicability of the proposed model.
by Rebecca B. Dupaix.
Ph.D.
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Liu, Dehua. "Thermodynamic and glass transition behavior in CO2-Polymer systems emphasizing the surface region." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1149020480.
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Sarmadi, Abdolmajid. "Effect of heat treatment on dyeability, glass transition temperature, and tensile properties of polyacrylonitrile fibers (orlon 42)." Diss., Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/49836.
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Deniers of treated and untreated fibers were determined and the „
results were used in calculations of tenacity and initial modulus.
Tensile properties were measured on a constant—rate—of—extension
machine. Shrinkage of treated and untreated fibers were measured
after they were boiled in water for 15 min. The glass transition
temperatures (Tg) were obtained by differential scanning calorimetry.
The ratio of the intensities of the CN/CH stretching bands were found
by infrared spectroscopy, using the KBr methodPh. D.
incomplete_metadata
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Vogtmann, Dana E. "Stress relaxation in poly(methyl methacrylate) (PMMA) during large-strain compression testing near the glass transition temperature." Connect to resource, 2009. http://hdl.handle.net/1811/36980.
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Truong, Vinh. "Modelling of the glass transition temperature of sugar-rich foods and its relation to spray drying of such products /." [St. Lucia, Qld.], 2003. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe17253.pdf.
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Chen, Kai. "Thermal behavior of model polystyrene materials exploring nanoconfinement effect /." Birmingham, Ala. : University of Alabama at Birmingham, 2007. https://www.mhsl.uab.edu/dt/2009r/chen.pdf.
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Thesis (Ph. D.)--University of Alabama at Birmingham, 2007.Title from PDF title page (viewed Jan. 28, 2010). Additional advisors: Derrick R. Dean, Wiliam K. Nonidez, Andrei Stanishevsky, Charles L. Watkins. Includes bibliographical references.
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Black, Victoria J. "High temperature supercapacitors." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12490.
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The scientific objective of this research program was to determine the feasibility of manufacturing an ionic liquid-based supercapacitor that could operate at temperatures up to 220 °C. A secondary objective was to determine the compatibility of ionic liquids with other cell components (e.g. current collectors) at high temperature and, if required, consider means of mitigating any problems. The industrial motivation for the present work was to develop a supercapacitor capable of working in the harsh environment of deep offshore boreholes. If successful, this technology would allow down-hole telemetry under conditions of mechanical vibration and high temperature. The obstacles, however, were many. All supercapacitor components had to be stable against thermal decomposition up to T ≥ 220 °C. Volatile components had to be eliminated. If possible, the finished device should be able to withstand voltages greater than 4 V, in order to maximise the amount of stored energy. The internal resistance should be as low as possible. Side reactions, particularly faradaic reactions, should be eliminated or suppressed. All liquid components should be gelled to minimise leakage in the event of cell damage. Finally, any emergent problems should be identified.
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Nieves, Ian Ivan. "Effects of Electron Irradiation and Percent Composition on the Glass Transition Temperature and Damping of Boron-Epoxy Composites." W&M ScholarWorks, 1996. https://scholarworks.wm.edu/etd/1539626045.
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Alvarez, Donado René Alberto 1989. "Estudo de propriedades dinâmicas e termodinâmicas de líquidos formadores de vidros metálicos através de simulações computacionais." [s.n.], 2016. http://repositorio.unicamp.br/jspui/handle/REPOSIP/305733.
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Orientador: Alex AntonelliDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
Made available in DSpace on 2018-08-30T22:57:05Z (GMT). No. of bitstreams: 1 AlvarezDonado_ReneAlberto_M.pdf: 4171490 bytes, checksum: e9cef25e59956ed4e6201f408c88c61c (MD5) Previous issue date: 2016
Resumo: Através de simulações de dinâmica molecular (MD) estudou-se o comportamento da viscosidade como função da temperatura para a liga Cu46Zr47Al7 que apresenta uma transição dinâmica frágil - forte. A interação entre as partículas foi modelada pelo potencial Modified Embeddded Atom Method (MEAM). As simulações de dinâmica molecular foram feitas usando as equações de Nosé-Hover e a viscosidade foi calculada pela fórmula de Green-Kubo. Observou-se que para uma temperatura reduzida (Tg/T ) de 0.8, o comportamento da viscosidade muda de frágil para forte. Usando a equação de Vogel-Fulcher-Tammann (VFT) em nossos resultados da simulação, observou-se que os valores da viscosidade calculados acima de 0.8 não são bem descritos por este ajuste, o que pode ser entendido como uma mudança no comportamento da viscosidade depois de atingir essa temperatura. A regressão feita usando a equação do VFT deu um valor limitante inferior para a temperatura de transição vítrea de 650K, o qual é um valor próximo da temperatura de transição vítrea reportada para estas ligas
Abstract: By means of molecular dynamic simulation (MD) we studied the behavior of the viscosity of a Cu46Zr47Al7 alloy, as a function of temperature, which displays a fragile - strong transition. Interactions between particles are modeled using the Modified Embedded Atom Method (MEAM). For the molecular simulations, we used the Nosé-Hoover equations, while the Green-Kubo formula gave us the viscosity. It was observed that, for a reduced temperature (Tg/T ) of 0.8, the behavior of the viscosity changes from fragile to strong. Using the Vogel-Fulcher-Tammann (VFT) equation in our results from the simulation, we noticed that the viscosity values above of 0.8 reaching this temperature. The regression achieved by VFT equation gave us a lowerbound value of 650K for the glass transition, which is very close to the glass transition temperature reported for this kind of alloys
Mestrado
Física
Mestre em Física
1370420/2014
CAPES
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Duki, Solomon Fekade. "Topics in Hard and Soft Condensed Matter Physics." Case Western Reserve University School of Graduate Studies / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1232737384.
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Wen, Chengyuan. "Computational Studies of Polyetherimides: Beyond All-Atom Molecular Dynamics Simulations." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/104205.
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Polyetherimides are an important class of engineering thermoplastics used in a broad range of industries and applications because of their high heat resistance and stability, high strength and moduli, excellent electrical properties over a wide range of temperatures and frequencies, good processability, good adhesive properties, and chemical stability. All-atom molecular dynamics (MD) simulation is a useful tool to study polymers, but the accessible length and time scales are limited. In this thesis, we explore several computational methods that go beyond all-atom MD simulations to investigate polyetherimides. First, we have developed a transferable coarse-grained MD model of polyetherimides that captures their mechanical and thermal expansion properties. Our results show that in order to make the model transferable, it is critical to include an entropic correction term in the coarse-grained force field and require the coarse-grained model to capture the thermal expansion property of polyetherimides. Secondly, we have constructed a predictive model of the glass transition temperature (Tg) for polyimides by using machine-learning algorithms to analyze existing data on Tg reported in the literature. The predictive model is validated by comparing its predictions to experimental data not used in the training process of the model. We further demonstrate that the diffusion coefficients of small gas molecules can be quickly computed with all-atom MD simulations and used to determine Tg. Finally, we have developed a Monte Carlo (MC) program to model the polymerization process of branched polyetherimides and to compute their molecular weight distribution for a wide range of systems, including fully reacted, partially reacted, stoichiometric, and nonstoichiometric ones. The MC results are compared to the predictions of the Flory-Stockmayer theory of branched polymers and an excellent agreement is found below the gel point of the system under consideration. Above the gel point, the Flory- Stockmayer theory starts to fail but the MC method can still be used to quickly determine the molecular weight distribution of branched polyetherimides under very general conditions.Doctor of Philosophy
Polyetherimides are an important category of engineering plastics with wide applications in many fields because of their superior mechanical, thermal, chemical, and electrical properties. All-atom molecular dynamics simulations serve as a useful tool to study the properties of polyetherimides in silico. However, such simulations are computationally expensive and therefore limited to small system sizes and short time scales. To overcome these issues, we employed various computational techniques in this thesis to model polyetherimides. First, we have developed a coarse-grained model of polyetherimides where atoms are grouped into beads. We show that molecular dynamics simulations on the basis of the coarse-grained model can be used to provide a reasonable description of the mechanical and thermal expansion properties of polyetherimides. Secondly, we have constructed a predictive model of the glass transition temperature, which is the temperature at which a material enters a glassy state when cooled rapidly, of polyimides using machine-learning algorithms. This model is capable of estimating the glass transition temperature of polyimides within an accuracy of ± 15 K even for those not synthesized yet. We further show that the diffusion coefficients of gas molecules, in addition to the polymer density, can be computed accurately with all-atom molecular dynamics simulations and used to determine the glass transition temperature of polyimides. Finally, we have developed a Monte Carlo scheme to efficiently model the polymerization and compute the chain-length distribution of branched polyetherimides under very general conditions. The results from Monte Carlo simulations are compared to the predictions of the Flory-Stockmayer theory of branched polymers. The range of applicability of the theory is revealed. Overall, we have demonstrated several computational techniques that can be used to efficiently model polyetherimides, potentially other polymers as well, beyond the widely-used all-atom molecular dynamics simulations.
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Pedoto, Giuseppe. "Characterization and Modelling of the Thermomechanical and Ageing Behavior of PEKK and C/PEKK Composites for Aircraft Applications at High Temperatures (above the Glass Transition Temperature) Characterization of the mechanical behavior of PEKK polymer and C/PEKK composite materials for aeronautical applications below and above the glass transition temperature." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2020. http://www.theses.fr/2020ESMA0011.
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La sensibilisation accrue aux questions environnementales concerne aujourd'hui les structures aéronautiques en termes d'impact environnemental et traitements de fin de vie. Dans cette optique,la possibilité de remplacer, dans les composites à matrice organique (CMO) utilisés pour des applications aéronautiques, leur matrice thermodurcissable non recyclable par une matrice thermoplastique recyclable est étudiée. En outre, les polymères thermoplastiques, tels que le PEKK, ont la possibilité d'être utilisés dans des structures plus chaudes (par exemple le pylône d'un avion), faisant l'objet de sollicitations de longue durée (fluage). Les températures de service de ces structures plus élevées que celles de la température de transition vitreuse du PEKK : il en découle, dans le matériau, une perte de propriétés due au changement d'état de solide à caoutchoutique, et éventuellement l'activation de phénomènes de cristallisation etde dégradation, qui pourraient également interagir. Ce travail vise à identifier et à modéliser ces mécanismes caractérisant le comportement du PEKK, dans ces conditions extrêmes particulières.Ceci est réalisé à partir de l'analyse des résultats des essais thermomécaniques, physico-chimiques et thermomécaniques couplés avec l’oxydation. Le modèle analytique 1-D du comportement duPEKK qui résulte de l’analyse des essais est étendu en 3-D et implémenté dans une méthode d'homogénéisation/localisation semi-analytique multi-échelle pour simuler le comportement dans mêmes conditions de composites stratifiés à matrice PEKK, en faisant varier l'orientation des plis et la séquence d'empilementThe nowadays increased awareness towards environmental issues concerns aircraft structures in terms of environmental impact and end-of-life disposal. In this optics, the possibility of replacing in the organic matrix composites (CMO) employed for aircraft applications the non-recyclable thermosetting matrix with a recyclable thermoplastic one is investigated. Moreover, thermoplastic polymers, such PEKK, have the possibility of being employed in warmer structures (e.g. the aircraft pylon), undergoing long duration solicitations (creep).The service temperatures for those structures are higher than the PEKK glass transition temperature, provoking, in the material, a loss of properties deriving from a change of state from solid to rubber, and possibly the activation of crystallization and degradation phenomena, which could also interact. This work aims to identify and model the mechanisms characterizing PEKK behavior, under the structure operative service conditions. This is achieved from the analysis of the results of thermomechanical, physical-chemical and coupled thermomechanical/oxidation tests. The resulting 1-D analytical model of the PEKK behavior, is extended in 3-D and implemented in a multi-scale semi-analytical homogenization / localization method to simulate PEKK based composites under the same conditions, varying the plies orientation and stacking sequence
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Gauthier, Mario. "The effects of matrix glass transition temperature and polarity, and ionic group spacers on ion aggregation in styrene ionomers /." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75935.
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Matrix glass transition temperature depression through internal plasticization of a styrene-sodium methacrylate ionomer resulted in enhanced clustering at low plasticization levels (up to ca. 20 mole%). At higher plasticization levels, ion aggregation was strongly disrupted. Matrix polarity effects were studied by nitrating the styrene units of the same ionomer. A sample with a relaxed dielectric constant comparable to acrylate polymers showed no decrease in clustering. Similarly, plasticization with nitrobenzene resulted in typical nonpolar diluent behavior. Polarity was, therefore, not a significant parameter affecting ion aggregation. New styrene copolymers with substituents R = $-$(CH$ sb2$)$ sb{ rm n}$COOMe (n = 1, 5, 10) or R = $-$O(CH$ sb2$)$ sb{ rm n}$COOMe (n = 1, 4, 10) in the para- position were synthesized, to form a systematic investigation of ionic group spacing effects on the dynamic mechanical properties of ionomers. The results were rationalized in terms of bulkiness and rigidity of the units supporting the ionic groups, and polymer backbone immobilization efficiency. Ion solvation effects were also suggested for the ether derivatives.
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La, Fuente Arias Carla Ivonne. "Efeito da etapa de resfriamento sobre as caracterísitcas de crocância e cor na obtenção de banana nanica crocante por secagem com pulso a alta temperatura." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/256032.
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Orientador: Celso Costa LopesDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos
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Resumo: Neste trabalho estudou-se a secagem de banana Nanica empregando um pulso inicial a alta temperatura e curto tempo (150°C e 15 minutos), seguido de uma etapa de resfriamento e uma etapa de secagem convencional a ar quente a 70°C. Na primeira parte do trabalho, avaliou-se especificamente a etapa de resfriamento pós-pulso HTST quanto aos atributos de crocância, encolhimento e cor no produto terminado. Analisaramse também as mudanças estruturais através de microscopia ótica. Na segunda parte do trabalho, estudou-se a temperatura de transição vítrea, através de Calorimetria Diferencial de Varredura, em bananas submetidas a este processo de secagem. Os resultados mostraram que, na etapa de resfriamento, a redução gradual de temperatura associada com tempos longos foi importante para que o produto mantivesse a estrutura porosa e crocante, porém também ocasionou produtos com cor escura, com baixos valores de luminosidade. Em contraposição, a redução acelerada de temperatura na etapa de resfriamento ocasionou a perda da estrutura porosa, além de os produtos finais ficarem duros e encolhidos; no entanto, a degradação de cor foi menor. Uma redução gradual da temperatura, com amplitude de 10°C e período de 7,5 minutos, totalizando 75 minutos, mostrou-se adequada para a manutenção da estrutura porosa e crocante, com a menor degradação de cor. A temperatura de transição vítrea decresceu com o aumento do conteúdo de umidade, para todas as amostras, comprovando o efeito plasticizante da água. O início da crocância nas amostras, expressada em número de picos do gráfico força-deformação, foi identificada entre 11% e 6% de umidade (bu)
Abstract: This work studied the drying of banana Nanica employing an initial pulse at high temperature and short time (150°C and 15 minutes); a cooling stage and a final hot air drying at 70°C. In the first part of this work, it was analyzed the post-pulse stage, as attributes of crispness, shrinkage and color. The structural changes also had been analyzed with optical microscopy. In the second part of this work, glass transition temperature of banana, dried with the same process, was studied by Differential Scanning Calorimetry. The results showed that in the cooling stage, the gradual reduction of temperature with longer times, were important for the product retains the porous structure and crispness, but also caused the formation of dark color products with lowest values of brightness. On the other hand, the sudden reduction of temperature, in the cooling stage, caused the loss of the porous structure, and final products became harder and shrunken but with less color degradation. A gradual decrease of temperature with amplitude of 10°C and period of 7.5 minutes summarizing 75 minutes of the cooling stage, proved to be appropriate for the maintenance of porous and crispness structure, with less color degradation. The glass transition temperature decreased with increasing moisture content for all the samples, confirming the water plasticization effect. Crispness in the samples, expressed in peaks number in stress-strain graphs, was initially observed between 11% and 6% of moisture content (wb)
Mestrado
Engenharia de Alimentos
Mestre em Engenharia de Alimentos
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Xu, Shengyi. "Computational insight into kinetic control of star polymer structure and properties." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1499466088519005.
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Sills, Scott E. "Interfacial nanorheology : probing molecular mobility in mesoscopic polymeric systems /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/9832.
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Persson, Magnus. "Thermo-Oxidative Degradation of High Temperature Polyimide Composites : Characterization and Modeling of Composites Affected by an Extreme Environment." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-60494.
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Carbon fiber (CF) 8-harness satin weave, T650/Neximid system of [(+45/-45)/(0/90)]2S and [(0/90)]4S layup was manufactured using resin transfer molding (RTM). The material was cut into 3-point bending specimens and treated for 24 hours in a burn oven at T=(320,350,375,400,450 & 500)°C. The material was tested according to ASTM E1640-13 using dynamic mechanical thermal analysis (DMTA). Un-treated material showed Tg levels of 384°C and 392°C for the respective layups. It was found that pre-Tg treatment between 320-375°C affected this material parameter up to similar levels as previous studies of post Tg exposure for 2h to ~420°C [4]. Subjecting the material for post-Tg exposure at 400°C showed a rapid change up to ~480°C for [(0/90)]4S laminate. Indications that this resin system could reach levels above 500°C was found for [(+45/-45)/(0/90)]2S layup. However, one of these specimens were unfit for testing. DMTA tested material for 400°C showed indications of degradation, found by a broadening of the tan delta peak. This can be put in relation to epoxy where a similar behavior appear after 24h exposure at 150°C. Furthermore, it was showed that poor quality laminate, elevated mass loss at this temperature. When the material was subjected to as high temperatures as 450°C only remaining fibers were found. At 500°C these were almost fully oxidized. 400°C data was predicted by the use of activation energy along with TG extrapolation. It was possible to show that ~1/8 out of this 8-layered structure, (½ of each surface layer), was degraded after 400°C exposure for 24h, resulting in diffusion limited oxidation (DLO). Last but not least, DLO assumptions was used to predict the storage modulus change for thermo-oxidative degradation of 400°C samples with Classic Laminate Theory (CLT). A ~4% stiffness decrease was predicted by this method. The drop is regarded as a loss in tensile stiffness of the outer damaged layer. This was compared by 3-point bending DMTA data showing a ~7% decrease. This model could thus be regarded as a contributing factor for the stiffness decrease of this complex degradation process.Kolfiber, 8-harness satin väv, T650/NEXIMID system med [(+45/-45)/(0/90)]2S och [(0/90)]4S orientering, tillverkades via RTM. Från materialet tillverkades 3-punkts böjprover. Dessa behandlades i 24 timmar vid T=(320, 350, 375, 400, 450 & 500)°C, i en brännugn. Materialet testades i enighet med ASTM E1640-13 via DMTA. Obehandlat material visade Tg nivåer av 384°C och 392°C för de respektive uppläggningarna. Pre-Tg exponering, vid 320-375°C, påverkade Tg upp till liknande nivåer som tidigare studier, (post-Tg 2h), ~420°C [4]. När materialet utsätts för post Tg exponering under 24 timmar vid 400°C kunde man se en snabb förändring av Tg, upp till ~480°C för [(0/90)]4S laminatet. Från [(+45/-45)/(0/90)]2S laminatet kunde man dessutom se indikationer på att nivån kunde nå över 500°C. Däremot var en av dessa prov inte kvalificerad för test efter behandlingen. DMTA testat material för 400°C visade indikationer av nedbrytning, via en breddning av piken för tan-delta kurvan. Det var dessutom möjligt att se att laminat av sämre kvalitet påverkade viktminskningen signifikant högre vid denna exponering. När material utsattes för så höga temperaturer som 450°C var endas fiber kvar efter test, vilket vid 500°C nästan var fullt nedbrutna. 400°C data förutspåddes via extrapolering av TG och Arrhenius beräkning. Beräkningen ledde till en övre gräns för nedbrytningen. Vidare var det möjligt att visa att ~1/8 av dessa 8-lager bröts ner efter 24 timmars exponering vid 400°C. Nedbrytningen motsvarar ½ av vartdera ytlager via diffusions begränsad oxidation (DLO). Sist men inte minst, kunskapen om DLO användes för att förutspå styvhetsförändringen vid termo-oxiderande nedbrytning med hjälp av klassisk laminat teori (CLT). DLO antogs resultera i en volymfraktionsförändring i det yttersta lagret. Detta implementerades i CLT där man kunde beräkna en ~4% styvhetsminskning via denna modell där det yttre skadade lagret har en reducerad dragstyvhet. Från testade böjprover i DMTA kunde man se en verklig ~7% styvhetsminskning för samma exponeringsvillkor. Modellen kan därmed ses som en bidragande del av denna komplexa nedbrytningsprocess.
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Mapesa, Emmanuel Urandu. "Molecular dynamics of nanometric layers of glass formers in interaction with solid substrates." Doctoral thesis, Universitätsbibliothek Leipzig, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-155709.
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Broadband Dielectric Spectroscopy (BDS) in combination with a nanostructured electrode arrangement – which circumvents the conventional need to evaporate metal electrodes onto soft matter – is used to study the molecular dynamics of several glass forming materials
confined in nanometric (> 5 nm) layers. Other complementary experimental tools employed in this work include spectroscopic vis-Ellipsometry (SE), AC-chip calorimetry (ACC), X-ray reflectrometry (XRR), Differential Scanning Calorimetry (DSC) and Atomic Force Microscopy (AFM). The latter is used to characterize the topography of the samples and to determine their thicknesses. Under the conditions of annealing samples (Tg + 50K) in high oil-free vacuum (10E-6 mbars) for at least 12 h and carrying out measurements in inert (dry nitrogen or argon) atmosphere, it is found for all studied thin layers that the
structural relaxation, and hence the dynamic glass transition – in its mean relaxation times – remains within a margin ±3 K from the respective bulk behaviour. It is revealed, inter alia, that the one-dimensional confinement of thin films introduces restrictions on other (slower) molecular relaxation processes which manifest, depending on the specific system under investigation, as (i) an interruption of the end-to-end (normal mode) fluctuation of the chains, or (ii) a slowing down of the delta-relaxation when the system is cooled towards glass-formation. Furthermore, (iii) evidence is provided to show that the dimensionality of confinement plays a significant role in determining the resulting dynamics. A molecular understanding of these findings is given, and the discussion presented with respect to the
on-going international debate about dynamics in confinement.
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Wheeler, Megan Caroline. "Parameters Influencing the Corrosion Protection Service Life of Epoxy Coated Reinforcing Steel in Virginia Bridge Decks." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/9687.
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This study is an evaluation of epoxy coated reinforcing steel (ECR) and its ability to effectively provide corrosion protection in reinforced concrete highway bridge decks. An analysis was conducted on 10 bridge decks built in the state of Virginia between the years 1981 and 1995.
A total of 141 cores containing either ECR or bare steel were evaluated. A chloride solution was applied to the surface on a weekly cycle (for a total duration of 3.06 years) and a nondestructive electrochemical testing was performed on each core on a monthly cycle. Cores were also inspected for surface cracks, the thermal properties of the epoxy coating, and the concrete conditions at bar depth. The concrete was tested for saturation percentages, diffusion coefficients, and chloride contents, while the epoxy was tested for its glass transition temperature, moisture content, and amount of surface cracking.
The results indicate that the best predictor for estimating the times to corrosion initiation and cracking is the amount of chlorides present in the concrete encasing the ECR. The presence of chloride ions will have a determining effect on corrosion regardless of the epoxy coating condition. As a result, it is likely that ECR is not the solution to corrosion prevention and it is recommended that closer attention be given to improving concrete conditions that reduce the diffusion of chloride ions. The conclusion that ECR is an unreliable corrosion prevention method is in agreement with the results of previous studies.Master of Science
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Takeiti, Cristina Yoshie. "Estudo da influencia da transição vitrea sobre a instantaneização de maltodextrinas por processo de aglomeração umida." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/256350.
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Orientadores: Fernanda Paula Collares, Theo Guenter KieckbuschTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos
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Resumo: Maltodextrinas são oligossacarídeos solúveis em água, provenientes da hidrólise de amidos. As condições da hidrólise permitem definir a distribuição de massa molecular das maltodextrinas e, conseqüentemente, suas características funcionais podem ser ajustadas para aplicações distintas e específicas. Estes ingredientes são empregados em formulações de pós alimentícios prontos para o consumo e, portanto, o conhecimento de atributos que afetam sua reconstituição em água é determinante para o desenvolvimento desses produtos. Maltodextrinas comerciais com diferentes graus de dextrose-equivalente (DE) e provenientes de três fábricas nacionais distintas foram avaliadas quanto à: morfologia das partículas, teor de umidade, massa molecular, diâmetro médio, densidade aparente e real, porosidade, tempo de molhamento, tempo de dissolução, grau de cristalinidade, isotermas de sorção de umidade e temperatura de transição vítrea (Tg). Os pós comerciais apresentaram características morfológicas distintas, o que influenciou o seu desempenho quanto às propriedades de reconstituição em água. Os produtos que apresentaram características intermediárias de reconstituição foram submetidos a um processo de aglomeração por jato a vapor em mini-instantaneizador para melhorar suas qualidades tecnológicas. As condições de operação foram otimizadas por metodologia de superfície de resposta. O produto aglomerado de maltodextrina com DE igual a 10 apresentou o melhor rendimento e excelentes propriedades instantâneas, enquanto que, a maltodextrina com maior grau de DE, isto é, com menor Tg apresentou o menor rendimento de processo e um produto com piores características de reconstituição. A tendência geral indica que a morfologia e características instantâneas dos aglomerados obtidos foram influenciadas pela temperatura de transição vítrea. Um estudo complementar realizado em leito fluidizado com paredes de acrílico, utilizando soluções de maltodextrina como ligante entre partículas sólidas inertes, avaliou as condições de solidificação das pontes vítreas. A relação umidade vs temperatura obtida confirmou que o processo de aglomeração é influenciado pela massa molecular das amostras e, conseqüentemente, por suas Tgs. Esses parâmetros devem ser considerados no dimensionamento e/ou condições de operação de aglomeradores
Abstract: Maltodextrins are water soluble oligossacharides produced by starch hydrolysis. Their functional characteristics depend on their molecular mass distributions which can be taylormade for specific applications through the control of the process conditions during hydrolysis. Maltodextrin are widely used as ingredient in instant food powder mixes and the knowledge of their reconstitution attributes would assist the development of new formulations. Commercial maltodextrins produced by three different Brazilian manufacturers with dextrose-equivalent (DE) degrees ranging from 5 to 20 were evaluated with respect to morphology, moisture content, molecular mass distribution, average particle diameter, bulk and true densities, void fraction, wetting and dissolution times, crystallinity degree, equilibrium isotherms and glass transition temperature (Tg). The maltodextrin powder showed distinct morphological features, which influenced their water reconstitution abilities. The products with moderate instant properties were submitted to a steam jet agglomeration process in a pilot plant instantiser in order to improve their technological qualities. The operational conditions were optimized by surface response methodology. The general trend indicated that the agglomerates morphology as well as their instant properties are influenced by the glass transition temperature. The DE10 maltodextrin agglomerates showed the best process yield and superior instant properties. The agglomerates of maltodextrin with the highest DE, which has the lowest Tg , showed the lowest yield and poor reconstitution properties. A complementary study, conducted in an Plexiglassÿ fluidized bed equipment using maltodextrin solutions as ligand, evaluated the formation of vitreous bridges between inert particles. The moisture content/temperature relations obtained supported the assumption that the agglomeration process is influenced by the molecular mass of the samples and, consequently, by their Tgs. These parameters should be considered in the design and /or operational conditions of agglomerators
Doutorado
Tecnologia de Alimentos
Doutor em Tecnologia de Alimentos
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Beena, Unni Aparna. "Structuration and glass transition temperature of the adsorbed polymer layer : some insights in the property deviations of the ultra-thin polymer film." Thesis, Lorient, 2016. http://www.theses.fr/2016LORIS416/document.
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La miniaturisation est un paramètre important lors de la fabrication d’un dispositif. Les films minces de polymère, qui sont des composants essentiels de beaucoup d’entre eux, montrent des propriétés anormales quand leur épaisseur est réduite jusqu’à produire un film confiné. Ce travail est dédié à la compréhension des effets de confinements et des propriétés des films ultra-minces de polymère. Dans un premier temps, nous avons observé l’évolution de la densité des films de polymère en fonction de leur épaisseur au moyen de nanoparticules d’oxyde de cérium adsorbées sur les surfaces polymères. La deuxième étude a mis en évidence les domaines de stabilité/instabilité de tels films, ce qui a conduit à une méthode pour fabriquer des films stables de moins de 7 nm d’épaisseur grâce au rinçage avec un solvant adéquat. Dans l’étude suivante, il a été montré qu’il y avait une influence significative du solvant utilisé pour le rinçage sur les caractéristiques de la couche résiduelle de polymère. Pour finir, la température de transition vitreuse de la couche résiduelle de polymère a été étudiée, montrant l’existence de deux températures de transition vitreuse, indiquant deux états physiques de la couche de polymère résiduelle. Au final, ce travail contribue à une meilleure compréhension de la densité, stabilité et des propriétés de transition vitreuse des films minces de polymère confinés par leur épaisseurSize reduction is one of the very important factors considered during the device fabrication. Polymer thin films, which is a crucial component of many devices, shows numerous anomalous behaviors when they are confined by their thickness. This work is dedicated to understand the confinement effects and properties of ultrathin polymer films. At the very outset we observed the density evolution of polymer films with the film thickness by means of adsorbing ceria nanoparticles onto the polymer surfaces. The second study threw light on the stability/instability domains of such films, which led to a method for fabricating stable films which are less than 7nm, by means of rinsing with a good solvent. In the following study, it was found that there is a significant influence of solvent used rinsing on the characteristics of the polymer residual layer. Finally the glass transition behavior of the polymer residual layer was analyzed, which showed multiple glass transition temperatures, that points to the existence of two physical states in the polymer residual layer. Altogether, this work contributes towards a better understanding of the density, stability and glass transition properties of polymer films confined by their thickness
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Liu, Yanchun. "Synthesis and Characterization of Amorphous Cycloaliphatic Copolyesters with Novel Structures and Architectures." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/77999.
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A series of random and amorphous copolyesters containing different cycloaliphatic rings within the polymer chains were prepared by melt polycondensaton of difunctional monomers (diesters and diols) in the presence of a catalyst. These polyesters were characterized by nuclear magnetic resonance (NMR), size exclusion chromatography (SEC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), tensile tests and/or dynamic mechanical analysis (DMA). The copolyester based on dimethyl bicyclo[2.2.2]octane-1,4-dicarboxylate (DMCD-2) was observed to have a higher Tg, about 115ºC, than the other copolyesters with the same compositions in this study. For copolyesters containing different compositions of dimethyl-1,4-cyclohexane dicarboxylate (DMCD) and DMCD-2, the Tg increased linearly with the increase of DMCD-2 mole content. DMA showed that all of the cycloaliphatic copolyesters had secondary relaxations, resulting from conformational transitions of the cyclohexylene rings. The polyester based on DMCD-3 in the hydrolytic tests underwent the fastest hydrolytic degradation among these samples.
A new triptycene diol (TD) was synthesized and incorporated into a series of cycloaliphatic copolyester backbones by melt condensation polymerization. Straight chain aliphatic spacers, including ethylene glycol (EG), 1,4-butanediol (BD) and 1,6-hexanediol (HD), were used as co-diols to explore their effects on polyester properties.
An analogous series of non-triptycene copolyesters based on various hydroxyethylated bisphenols were also prepared for comparison. The results revealed that the TD-containing polymers had higher thermal stability and higher Tg's than the corresponding non-TD analogs. For TD-containing copolyesters, the mechanical properties were found to be dependent on the types and compositions of the co-diols. A 1,4-butanediol-based triptycene copolyester was observed to have a significantly increased Tg and modulus while maintaining high elongation at ambient temperature. Furthermore, it was demonstrated that the triptycene polyester exhibited higher Tg and modulus than those containing bisphenol derivatives. However, all of the 1,4-butanediol based copolyesters were brittle and had comparable moduli at low temperatures (-25°C or -40 °C).
Melt polycondensation was also used to prepare a series of all-aliphatic block and random copolyesters including the following aliphatic monomers: trans-DMCD, DMCD-2, neopentyl glycol (NPG), diethylene glycol (DEG) and dimethyl succinate (DMS). The polymer compositions were determined by 1H NMR, and the molecular weights were determined using SEC. The polyesters were also characterized by TGA, DSC, DMA and tensile tests. Phase separation was not observed in these block copolyesters. However, the block copolyester containing DMCD-2 and NPG was observed to have a higher Tg than the block copolyester based on trans-DMCD and NPG. In addition, these block copolyesters were found to have better mechanical properties than the corresponding random copolyesters.Ph. D.
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Qadir, Adnan. "Investigation Of Low Temperature Cracking In Asphalt Concrete Pavement." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612696/index.pdf.
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In this study, low temperature cracking of asphalt concrete is investigated based on a laboratory experimental program including the design variables of aggregate type, gradation, asphalt content, binder grading, binder modification, and the experimental variables of cooling rate, and specimen size. The design of experiment is proposed according to the fractional factorial design principles to reduce the required number of test specimens. Mix designs are performed according to the Superpave mix design guidelines using materials obtained from the Turkish General Directorate of High-ways. In the course of this study, a test setup for thermal stress restrained specimen test for asphalt concrete is developed and used successfully to test a number of as-phalt concrete beam specimens. The same setup is also used for measuring the glass transition temperatures to obtain various thermo-volumetric properties of mixtures. Statistical methods are used to identify the effect of experimental variables on frac-ture strength, fracture temperature and other dependent variables obtained from the testing program. Statistical models are also developed to predict the fracture strength, fracture temperature and other thermo-volumetric properties of mixtures. Results of analyses show that aggregate type, binder modification, and asphalt content significantly affect both the fracture strength and fracture temperature of asphalt concrete. While the glass transition temperature is affected by only aggregate type, coefficients of contraction before and after the glass transition temperature are not influenced by any of the experimental variables. The results of this study provide an important basis to prevent low temperature cracking in asphalt concrete pavements.
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Henann, David Lee. "A constitutive theory for the mechanical response of amorphous metals at high temperatures spanning the glass transition temperature : application to microscale thermoplastic forming of Zr₄₁.₂Ti₁₃.₈Cu₁₂.₅Ni₁₀Be₂₂.₅." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44885.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references.
Bulk metallic glasses (BMGs) are a promising emerging engineering material distinguished by their unique mechanical properties and amorphous microstructure. In recent years, an extremely promising microscale processing method for bulk metallic glasses, called thermoplasticforming has emerged. As with any emerging technology, the scientific basis for this process is at present fragmented and limited. As a result their is no generally agreed upon theory to model the large-deformation, elastic-visco-plastic response of amorphous metals in the temperature range relevant to thermoplastic-forming. What is needed is a unified constitutive framework that is capable of capturing the transition from a elastic-visco-plastic solid-like response below the glass transition to a Newtonian fluid-like response above the glass transition. We have developed a finite-deformation constitutive theory aimed to fill this need. The material parameters appearing in the theory have been determined to reproduce the experimentally measured stress-strain response of Zr₄₁.₂Ti₁₃.₈Cu₁₂.₅Ni₁₀Be₂₂.₅ (Vitreloy-1) in a strain rate range of [10-5, 10-1] s-1, and in a temperature range [593, 683] K, which spans the glass transition temperature [nu]9 = 623K of this material. We have implemented our theory in the finite element program ABAQUS/Explicit. The numerical simulation capability of the theory is demonstrated with simulations of micron-scale hot-embossing processes for the manufacture of micro-patterned surfaces.
by David Lee Henann.
S.M.
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Moghaddas, Mohamad Amin. "Comparison of Computational Modeling of Precision Glass Molding of Infrared Lenses." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397599181.
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Mitton, Renata. "Tuning the Physical Properties of Poly(arylene ether)s Prepared from 3,5-Difluorobenzene Sulfonamides." Wright State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=wright1436957462.
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Zhang, Lizhong. "Physical, mechanical, thermal, and viscoelastic properties of water-blown rigid polyurethane foam containing soy flours /." free to MU campus, to others for purchase, 1998. http://wwwlib.umi.com/cr/mo/fullcit?p9924871.
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Hofsetz, Kelly 1976. "Propriedades fisicas e transições de fase da banana nanica submetida a secagem com pulso HTST (inicial)." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/256033.
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Orientador: Celso Costa LopesTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos
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Resumo: Neste trabalho estudou-se a secagem de banana utilizando um pulso inicial a alta temperatura e curto tempo, combinado com uma etapa de secagem convencional a ar quente a 70°C. Numa primeira etapa, foram analisadas as mudanças de encolhimento, porosidade e estrutura ao longo da secagem com bananas de origem portuguesa e brasileira. Esses resultados foram comparados com os de uma secagem convencional feita somente a 70°C. Na segunda etapa, estudaram-se as isotermas de sorção e as transições de fase nas amostras das duas origens (Portugal e Brasil) através de Calorimetria Diferencial de Varredura. Os resultados da primeira parte mostraram que o grau de encolhimento da banana foi maior para a secagem convencional a 70°C, na qual o volume apresentou um decréscimo linear com o conteúdo de umidade, chegando a 30%, enquanto que a porosidade aumentou progressivamente até 32%. A secagem combinada resultou na formação de um produto com uma estrutura altamente porosa (45,5% a 57,5%) e menor grau de encolhimento (42% a 68,5%), quando comparada com a secagem convencional a 70°C. As observações estruturais nas amostras de banana ajudaram a explicar as mudanças na porosidade e encolhimento. Os resultados das isotermas de sorção tiveram um bom ajuste para o modelo de BET e de GAB para as amostras frescas de origem portuguesa e, para as amostras secas das duas origens, o modelo de GAB foi o mais adequado. A ocorrência da temperatura de transição vítrea foi verificada em todas as amostras estudadas e decresceu com o aumento do conteúdo de umidade, comprovando o efeito plasticizante da água. O modelo de Gordon-Taylor permitiu uma boa predição da dependência da temperatura de transição vítrea com o conteúdo de água para as amostras de origem portuguesa. No caso das amostras de origem brasileira, foi encontrada uma relação de dependência linear do parâmetro kGT do modelo de Gordon-Taylor com a temperatura de transição vítrea experimental
Abstract: This study was conducted to evaluate the drying of bananas by a high temperature and short time drying pulse combined with hot air-drying process stage at 70°C. Firstly, Portuguese and Brazilian bananas samples were dried and the changes of shrinkage, porosity and structure during drying were analyzed. This results were compared with those obtained in a conventional air-drying process at 70°C. After that, sorption isotherms of samples from Portugal and Brazil, as well the phase transitions of the Brazilian banana, were studied. The results of the first part showed that shrinkage changes during drying was more intense to the conventional air-drying process at 70°C, and a line ar decrease in volume with the decrease in moisture ratio was observed reaching 30%, while the porosity increased uniformly reaching values of about 32%. The high temperature and short time drying pulse combined with hot air- drying process stage at 70°C resulted in the formation of a highly porous structure (45,5% to 57,5%) and reduced shrinkage (42% to 68,5%) when compared with the conventional air-drying process. Structural observations of the banana samples during the processes studied were able to explain the volume and porosity changes. The BET and GAB equations gave the best fit to the experimental sorption data for Portuguese fresh bananas and the GAB model was found to be the best-fitted equation for all dried bananas (Portuguese and Brazilian samples) and both models gave information about the shelf-stability for the samples. The glass transition temperature occurred for all samples studied and decreased as water content increased, confirming the water plasticization effect. The Gordon-Taylor equation was able to predict the dependence of the glass transition temperature on moisture content for the Portuguese fresh samples. A linear dependence of the kGT (Gordon-Taylor equation¿s constant) and the experimental glass transition temperature was found for the Brazilian samples
Doutorado
Doutor em Engenharia de Alimentos
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Piovesan, Victor. "Relations composition – structure – propriétés des verres peralumineux pour le conditionnement des déchets nucléaires." Thesis, Orléans, 2016. http://www.theses.fr/2016ORLE2064/document.
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Dans le cadre de la recherche sur le conditionnement des déchets nucléaires issus des combustibles usés, de nouvelles formulations vitreuses sont à l’étude. Ces nouvelles matrices doivent être capables d’incorporer une importante teneur en produits de fission et actinides mineurs (PFA) tout en présentant d’excellentes propriétés en termes d’homogénéité, stabilité thermique, comportement à long terme et faisabilité technologique. Cette étude s’intéresse aux verres dits « peralumineux », c’est-à-dire à des verres présentant un excès d’ions aluminium vis-à-vis des ions compensateurs de charges (Na⁺, Li⁺ et Ca²⁺). Une approche par plan d’expériences a été réalisée afin de déterminer les relations entre la composition de systèmes peralumineux simplifiés à sept oxydes (SiO2 – B2O3 – Al2O3 – Na2O – Li2O – CaO – La2O3) et leurs propriétés physico-chimiques : viscosité, température de transition vitreuse et microstructure. Une étude structurale réalisée par spectroscopie RMN a également permis de mieux définir les rôles structuraux de Na⁺, Li⁺ et Ca²⁺ au sein des verres peralumineux ainsi que l’organisation structurale de ces matrices. Par la suite, des verres peralumineux complexes ont été élaborés et caractérisés afin d’une part, de valider la transposition des résultats entre verres simplifiés et verres complexes et d’autre part, de souligner la potentialité des verres peralumineux comme matrice de conditionnementPart of the Research and Development program concerning high level nuclear waste conditioning aims to assess new glass formulations able to incorporate a high waste content with enhanced properties in terms of homogeneity, thermal stability, long term behavior and process ability. This study focuses on peraluminous glasses, defined by an excess of aluminum ions Al³⁺ in comparison with modifier elements such as Na⁺, Li⁺ or Ca²⁺. A Design of Experiment approach has been employed to determine relationships between composition of simplified peraluminous glasses (SiO2 – B2O3 – Al2O3 – Na2O – Li2O – CaO – La2O3) and their physical properties such as viscosity, glass transition temperature and glass homogeneity. Moreover, some structural investigation (NMR) was performed in order to better understand the structural role of Na⁺, Li⁺ and Ca²⁺ and the structural organization of peraluminous glasses. Then, physical and chemical properties of fully simulated peraluminous glasses were characterized to evaluate transposition between simplified and fully simulated glasses and also to put forward the potential of peraluminous glasses for nuclear waste containment
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Ellgren, Alex. "Analysis of vortex movement in an YBCO thin film : Models of the vortex solid-to-liquid transition compared to a sensitive resistive measurement of a strongly pinned YBCO thin film." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-140589.
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When a high-temperature superconductor transitions in the presence of a magnetic field, the resistance does not immediately go to zero. Instead, the transition is smoothed by the resistive effects of moving vortices so that perfect conductivity isn't reached until several K below Tc, where the vortices have frozen into a glass state. The properties of this glass depend mainly on the amount and correlation between impurities in the superconductor. This report describes a study of the glass transition in an YBCO thin film rich in uncorrelated impurities. The aim was to use sensitive resistive measurements to determine which of two models of this transition, the vortex glass model and the vortex molasses model, is more accurate. After evaluation, both models are found lacking and a third model is put forth. This model, which resembles the normal distribution, excellently describes the YBCO thin film case. When the new model is tested against data from similar measurements, an YBCO single crystal and a TlBaCaCuO thin film, the results are mixed. Further study is suggested to determine the model's range of validity.
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Edling, Hans Eliot. "Synthesis and Structure-Property Relationships of Polyesters Containing Rigid Aromatic Structures." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/95029.
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Polyesters are an attractive class of polymer that can be readily modified with a wide range of different comonomers, during polymerization or with melt blending, to achieve a wide variety of physical properties. This research primarily focuses on polyesters that incorporate rigid aromatic structures that have excellent potential to enhance thermal and mechanical properties. Copolyesters were prepared through melt polycondensation of diesters and diols in the presence of an exchange catalyst. Monomer incorporation was verified with nuclear magnetic resonance (NMR) and molecular weights were obtained by measuring inherent viscosity (ninh). Physical properties were assessed with thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and rheology. Mechanical properties were assessed with tensile and impact testing.
Copolyesters of poly(ethylene terephthalate) (PET) were synthesized by substituting dimethyl terephthalate (DMT) with dimethyl 4,4'-biphenyldicarboxylate (4,4'BB) resulting in enhanced glass transition (Tg) temperatures relative to PET while affording melting temperatures (Tm) low enough to allow facile melt processing. Further modification with dimethyl isophthalate (DMI) or dimethyl 3,4'-biphenyldicarboxylate (3,4'BB) slowed crystallization sufficiently to allow biaxial orientation, leading to further studies assessing the permeability of oriented films.
Novel amorphous polyesters were synthesized with 3,4'BB or 4,4'BB in combination with neopentyl glycol (NPG), 1,4-cyclohexandimethanol (CHDM) and ethylene glycol (EG). Use of multiple diols produced clear, amorphous copolyesters with Tgs as high at 129 C.
A series of novel high temperature(Tm) copolyesters were synthesized from dimethyl 2,6-naphthalenedicarboxylate (DMN) and 4,4'BB combined with CHDM. Studies were performed with standard DSC and thin film calorimetry to show the convergence of multiples melting endotherms in an effort to determine their origin. Preliminary work was performed on the modification of poly(1,4-cyclohexylenedimethylene terephthalate) (PCT), poly(1,4-cyclohexylenedimethylene 2,6-naphthalate) (PCN) and poly(1,4-cyclohexylenedimethylene 4,4'-bibenzoate) (PCB) with dimethyl p-terphenyl-4,4''-dicarboxylate.PHD
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Budhavaram, Naresh Kumar. "Facile protein and amino acid substitution reactions and their characterization using thermal, mechanical and optical techniques." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/40340.
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The work focused on addressing four main objectives. The first objective was to quantify protein and amino acid substitution reactions. Michael addition reactions were used to modify the amino acids and protein. Amino acids alanine, cysteine, and lysine, and protein ovalbumin (OA) were substituted with different concentrations of ethyl vinyl sulfone (EVS). The substituted products were analyzed using Raman spectroscopy and UV-spectroscopy based ninhydrin assay. In case of alanine, Raman and UV results correlated with each other. With cysteine at lower EVS substitutions amine on the main chain was the preferred site while the substitution shifted to thiols at higher substitutions. This could only be discerned using Raman spectroscopy. Lysine has amines on the main chain and side chain while main chain amine was the most reactive site at lower concentrations of EVS while at higher concentrations side chain amines were also substituted. This information could be discerned using Raman spectroscopy only and not UV spectroscopy. In case of protein as observed by Raman and UV spectroscopy the reaction continued at higher concentrations of EVS indicating the participation of glutamine and asparagines at higher substitutions. However, the reaction considerably slowed down at higher EVS substitutions.
The second objective of the study was to decrease the glass transition temperature (Tg) of OA through internal plasticization and also study the effects of the substituents on the thermal stability of OA. The hypothesis was by covalently attaching substituents to OA, number of hydrogen bonds can be reduced while increasing the free volume and this would reduce Tg. EVS, acrylic acid (AA), butadiene sulfone (BS) and maleimide (MA) were the four groups used. EVS was the most efficient plasticizer of all the four substituents. The Tg decreased with the increasing concentration of EVS until all of the reactive of groups on OA were used up. Tg decreased slightly with AA and BS while no change was observed with MA. However, the substituents showed exact opposite trend in thermal stability as measured using thermogravimetric analysis (TGA). The thermal stability of MA substituted OA was the highest and that of EVS substituted OA was least. FT-IR spectroscopy results indicated that all four substituents caused structural changes in OA. This implied that there were intermolecular interactions between substituted protein chains in case of AA, BS, and MA. This caused an increase in the thermal stability. EVS on the other hand is a linear chain monomer with a hydrophobic end group and hence could not participate in the intermolecular interactions and hence caused a decrease in Tg. As mentioned above the limitation to this technique is the number of available reactive groups on the protein. However, we successfully demonstrated the feasibility of this method in decreasing Tg of protein.
The third objective was to create hydrogels by crosslinking OA with divinyl sulfone (DVS). Protein hydrogels due to their biocompatible nature find applications in drug delivery and tissue engineering. For tissue engineering applications the hydrogels need to be mechanically stable. In this study the protein was substituted with EVS or AA and then crosslinked with DVS. The swelling ratio was measured as a function of pH. All the hydrogels showed the same trend and swelled the least at pH 4.5 which is the isoelectric point of the protein. At basic pH conditions EVS substituted hydrogels swelled the most while AA substituted hydrogels showed least swelling. The static and dynamic moduli of the hydrogels were determined using tensile tester and rheometer respectively. The static modulus values were three times the dynamic modulus. The modulus of the control which is crosslinked OA was least and that of AA substituted OA was highest. The stress relaxation test also showed similar results in which AA substituted OA relaxed the most and the control relaxed the least. FT-IR of the dry hydrogels showed that the amount of hydrogen bonding increased with AA substitution. The hydrophilic AA end groups interacted with each other forming hydrogen bonds. These hydrogen bonds served as additional crosslinks there by increasing the modulus of the hydrogels. EVS on the other hand was incapable of interactions due to the lack of hydrophilic end groups. We were successfully able to create protein hydrogels and control the swelling and mechanical properties by varying the amount of substituted group.
The final objective of the study was to create and characterize microstructures from substituted alanine and lysine. Alanine and lysine were substituted with different concentrations of EVS. Bars and fibers were observed for alanine at moderate substitutions while at higher concentrations random structures were observed using scanning electron microscopy (SEM). Lysine formed tubes at moderate EVS substitutions and rosettes at high concentrations of EVS as evidenced by SEM. FT-IR results suggested that instead of carbonyl one of sulfonyl bonded to the available amine in modified amino acids. And only in this case fibers, tubes and rosettes were observed. X-ray diffraction (XRD) results supported this observation. Using these results we hypothesized that the self assembled structures very much depended on the amount of EVS present in the substituted product and sulfonyl forming β-sheet analogs with amine.Ph. D.
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Andrejevic, Marina. "Functionalized Sulfone and Sulfonamide Based Poly(arylene ether)s." Wright State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=wright1402073837.
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Sánchez, Sáenz Carolina Maria 1978. "Secagem contínua de raízes de chicória com aplicação de radiação infravermelha em um secador agitador/misturador." [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/257102.
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Orientadores: Rafael Augustus de Oliveira, Kil Jin ParkTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agrícola
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Resumo: As pesquisas atuais em secagem de alimentos levam em consideração a qualidade do produto e a eficiência energética do processo, já que este processo consome cerca de 20-25% da energia utilizada pelo processamento na indústria de alimentos. Isto faz com que sejam exploradas novas técnicas e combinações de métodos de secagem e avaliação da intermitência do processo. Assim, realizou-se mais um estudo com o secador agitador/misturador (patente PI 0506639-5), iniciando pela adequação das pás do eixo misturador e adaptação do sistema de controle de velocidade e aquecimento do ar. O tempo de residência foi determinado considerando a rotação do eixo das pás e a rotação do eixo de alimentação do secador. Foi avaliada a influência dos parâmetros de secagem sobre o processo, de modo que foi possível determinar as melhores condições de pré-secagem HTST (High Temperature and Short Time) combinada com a secagem convectiva contínua com aplicação de radiação infravermelha, para obtenção de um produto de qualidade e com baixa demanda de energia elétrica no processo. Foi feito também o estudo da influência desses processos nas propriedades físicas e mecânicas de raízes de chicória. A redução da demanda de energia elétrica foi obtida considerando a intermitência da aplicação de radiação infravermelha. Os testes e análises realizados nestas condições resultaram em uma série de dados que garantem que a combinação de métodos de secagem e de técnicas de intermitência são eficientes energeticamente e resultam em um produto de boa qualidade
Abstract: In recent research works, food drying takes into account product quality and energy efficiency of process, since drying process consumes about 20-25 % of the energy used by the food processing industry. This fact indicates that new techniques combining drying methods and intermittency of the process must be evaluated. Thus, a study with the agitator / mixer dryer (patent PI 0506639-5) was performed, beginning with the mixer blades adequacy and velocity control and air heating systems adaptation. Residence time distribution determination has been conducted, considering rotation of blades and feed rotation of dryer. The influence of dying parameters on the process was evaluated, so that it was possible to determine the best conditions of HTST (High Temperature and Short Time) drying combined with the continuous drying with pulse of infrared radiation application, to obtain a good quality dried product and electric energy efficiency of the process. Study the influence of these processes was also done on the physical and mechanical properties of chicory roots. Finally, the electric energy efficiency was obtained considering the intermittency of pulse infrared radiation application. The experimental runs and analyses under these conditions have generated data which ensure that the combination of drying methods and intermittency techniques are energy efficient and result in a good quality product
Doutorado
Tecnologia Pós-Colheita
Doutora em Engenharia
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Osborn, Shawn James. "Morphological and Mechanical Properties of Dispersion-Cast and Extruded Nafion Membranes Subjected to Thermal and Chemical Treatments." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/37517.
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The focus of this research project was to investigate morphological and mechanical properties of both extruded and dispersion-cast Nafion® membranes. The project can be divided into three primary objectives; obtaining a fundamental understanding of the glass transition temperature of Nafion®, determining the effect of thermal annealing treatments on the morphology and mechanical properties of dispersion-cast Nafion®, and examination of dispersion-cast Nafion® subjected to an ex-situ, Fentonâ s chemical degradation test. Nafion®, a perfluorosulfonate ionomer, is considered a commercially successful semi-crystalline ionomer with primary applications in chlor-alkali cells and proton exchange membrane fuel cells.
With the aid of dynamic mechanical analysis (DMA) and dielectric spectroscopy (DS), we were able to provide definitive evidence for a genuine glass transition in Nafion®. DMA of Nafion® samples that were partially neutralized with tetrabutylammonium counterions showed a strong compositional dependence suggesting that the β-relaxations of H+-form Nafion® and the neutralized ionomers have the same molecular origin with respect to backbone segmental motions. Building upon our previous studies of the molecular and morphological origins of the dynamic mechanical relaxations of Nafion® neutralized with a series of organic ions, the glass transition temperature of H+-form Nafion® is now confirmed to be the weak β-relaxation centered at -20 °C. Dielectric spectra also showed this transition from the perspective of dipole relaxation. The signature of cooperative long range segmental motions in dielectric spectra was seen here, as with other polymers, mainly through the excellent agreement of the β-relaxation time-temperature dependence with the Vogel-Fulcher-Tammann equation.
We have also discovered that new dispersion-cast H+ form Nafion® membranes are susceptible to disintegration/dissolution when subjected to boiling methanol. In this work, we have achieved significant decreases in the percent solubility of H+-form Nafion® by either thermally annealing above 175 °C or solution-processing at 180 °C using a high boiling point solvent. Small Angle X ray Scattering (SAXS) displayed a change in the morphology of H+ form membranes with increasing annealing temperature by a shift in the crystalline scattering peak (q â 0.05 à 1) to lower q values. Counterion exchange of Nafion® from H+ to Na+ form had no influence on the membraneâ s susceptibility to disintegration in boiling methanol. In order to achieve mechanical stability in boiling methanol, Na+ form membranes had to be annealed at 275 °C for at least fifteen minutes. The SAXS data of annealed Na+ form membranes showed a dramatic decrease in crystalline order with annealing temperature, ultimately leading to the disappearance of the crystalline scattering peak after fifteen minutes at 275 °C. The onset of methanol stability with the melting of Nafion® crystallites suggests that chain entanglement is an important parameter in obtaining solvent stability.
With respect to chemical stability, we performed studies aimed at examining the effects of Fentonâ s Reagent on the resistance to radical attack of new generation, dispersion-cast Nafion®. Changes in the 19F solid-state NMR spectra of dispersion-cast Nafion® before and after chemical degradation via Fentonâ s Reagent predicts a rather random attack by â ¢OH and â ¢OOH radicals. Several membranes were also thermally annealed between 100-250 °C in an attempt to correlate crystallinity with chemical degradation kinetics of Nafion® via Fentonâ s Reagent. The results indicate that the effect of counterion exchange into the Na+ form was minimal, but the degree of thermal degradation had a tremendous effect on the fluoride release rate and chemical degradation kinetics. By exchanging the membranes into the Na+ form, thermal degradation was avoided, allowing us to study the role of crystallinity as a function of fluoride release. Ultimately, Nafion® crystallinity was deemed an important factor in deterring peroxide radical attack. As the percent crystallinity decreased with annealing temperature, the fluoride concentration in the resulting Fentonâ s media increased accordingly, indicating that the amorphous regions of the polymer are more susceptible to chemical degradation via peroxide radical attack.Ph. D.