Dissertations / Theses on the topic 'Elongational flow'
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Greener, James. "Elongational flow in ceramics processing." Thesis, Brunel University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294511.
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Smitter, Luis Manuel. "Study of the interactions between poly(ethylene oxide) and anionic surfactants in elongational flow." Diss., The University of Arizona, 2001. http://hdl.handle.net/10150/279813.
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The rheology of polymer solutions is important in a wide variety of applications. In particular, solutions of high-molecular-weight, flexible polymers exhibit an increase in their apparent extensional viscosity with strain rate under extensional flow conditions. This extension thickening is due to formation of transient entanglements of polymer molecules. Certain commercial fluids contain both polymers and surfactants that might interact at the molecular level. These interactions affect the conformation of the polymer chain and, therefore, the rheological behavior of the solution. For instance, addition of anionic surfactants to solutions of nonionic polymers is known to induce increases in the shear viscosity of aqueous solution. This work investigates the behavior of aqueous solutions of a high-molecular-weight poly(ethylene oxide) (PEO), a nonionic, flexible polymer, and the anionic surfactants sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS) and a commercial alpha-olefin sulfonate (AOS) in extensional flows. The extensional rheology of polymer/surfactant solutions is studied in an opposed-jets device, which generates a flow field close to uniaxial extension. For PEO/SDS mixtures, the results show that formation of micellar aggregates of SDS along the PEO chains results in an increase in the strength of extension thickening of PEO solutions by promoting intermolecular interactions between polymer chains. The minimum PEO concentration required to form intermolecular entanglements is substantially reduced in the presence of micellar aggregates. In solutions containing NaCl, intramolecular interactions are observed at low PEO concentrations. These reduce the strength of extension thickening. Addition of a co-solvent is investigated. The presence of alcohols in the aqueous solutions affects their rheology by changing the solvent nature for both PEO and SDS. In particular, n-octanol promotes aggregation of SDS along the PEO chains, enhancing intermolecular network formation in extensional flow. Results with mixtures of PEO with sulfonated surfactants (SDBS and AOS) show that both intermolecular and intramolecular interactions are promoted by these surfactants, depending on PEO concentration and molecular weight. The effect of ageing on these polymer/surfactant systems was studied. In extensional flows, extension thickening is suppressed in solutions of PEO with SDBS or AOS over a few-day period, whereas PEO and PEO/SDS solutions show no change.
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Frascoli, Federico. "Chaotic and rheological properties of liquids under planar shear and elongational flows." Swinburne Research Bank, 2007. http://hdl.handle.net/1959.3/22416.
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Thesis (PhD) - Swinburne University of Technology, Centre for Molecular Simulation - 2007.Dissertation submitted in fulfilment of requirements for the degree Doctor of Philosophy, Centre for Molecular Simulation, Faculty of Information and Communication Technologies, Swinburne University of Technology, 2007. Typescript. Includes bibliographical references (p. 151-161).
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Recktenwald, Steffen Michael [Verfasser], and N. [Akademischer Betreuer] Willenbacher. "Flow Instabilities of Dilute Surfactant Solutions in Elongational Deformations / Steffen Michael Recktenwald ; Betreuer: N. Willenbacher." Karlsruhe : KIT-Bibliothek, 2019. http://d-nb.info/1190178834/34.
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Hadinata, Chitiur, and chitiurh@yahoo com au. "Flow-induced crystallization of polybutene-1 and effect of molecular parameters." RMIT University. Civil, Environmental and Chemical Engineering, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080212.163803.
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There are two main goals of this thesis: to investigate the flow-induced crystallization behaviour of Polybutene-1 (PB-1 samples, and to study the effects of molecular parameters on the crystallization behaviour While flow-induced crystallization is not a new area in polymer research, well-defined experimental methods that allow access to high flow rate range comparable to that encountered in real processing are still lacking. Two types of flow are considered: shear and uniaxial elongational. Regarding the second aim, several molecular parameters considered are: molecular weight, molecular weight distribution, isotacticity, presence of nucleating agents, and copolymer content. For this purpose an array of PB-1 samples were used. It is found that each of these parameters can have significant effect on the crystallization behaviour. Mainly rheological methods were utilized to conduct the flow-induced crystallization experiments. Crystallization onset time is define d from the change in viscosity or other related parameters. The experiments begin with low shear rate range, to ensure that the results are comparable with literature data. In this range we encounter the quasi-quiescent onset time at very small. shear rates, which draws an interesting comparison with another physical parameter, the gel time. Beyond a critical flow rate a decrease in the onset time is seen, and a plateau-and-slope trend is evident for a curve of onset time vs. shear rate. Using a combination of three experimental methods, shear rates ranging from Q0001 - 500 s-1 are successfully achieved, and a good agreement between these methods is observed. Furthermore, a normalization procedure is introduced, which yields temperature-invariant curves for the mentioned range of shear rate. For the uniaxial elongation flow, the Elongational Viscosity Fixture (EVF) is employed, with the strain rate ranging from 0.0001 - 10 s'. A greater reduction in onset time as compared to shear (at the same shear/strain r ate) is observed, and the difference in the onset times for shear and elongation already reaches more than one decade for a flow rate of 10 5. This quantitative comparison is particularly important; since not so many data on elongation-induced crystallization are available in the literature. Finally, the thesis compares several flow induced crystallization models that can be useful as prediction tools and selects one of these models to be compared with the experimental data. A qualitative agreement is found, however, for better quantitative prediction the model still needs to be.
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Georgieva, Kristina [Verfasser], and N. [Akademischer Betreuer] Willenbacher. "Clogging of Microchannels by Nano-particles due to Hetero-coagulation in Elongational Flow / Kristina Georgieva. Betreuer: N. Willenbacher." Karlsruhe : KIT-Bibliothek, 2013. http://d-nb.info/1033837318/34.
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Yu, Wei. "Development of an elongational-flow microprocess for the production of size-controlled nanoemulsions : application to the preparation of composite and hybrid polymeric microparticles." Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAE027/document.
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L’objectif de ce travail fut de développer et d’étudier les performances d’un microprocédé basse pression à écoulement élongationnel pour la production de nanoémulsions polymérisables de tailles contrôlées et de distributions de taille étroites. Le diamètre des nanogouttelettes a pu être précisément ajusté dans la gamme 50-300 nm en modifiant simplement les paramètres de procédé : le débit réciproque au travers du micromélangeur, le nombre de cycles et la dimension caractéristique du microcanal. Les nanoémulsions produites furent, dans une seconde étape, polymérisées par voie thermique ou par irradiation UV afin de générer des suspensions colloïdales de nanoparticules de polymère de tailles également contrôlées (87-360 nm). Un monomère, un agent de réticulation ainsi qu’un amorceur thermique ou photochimique appropriés furent par la suite ajoutés au milieu continu de ces nanosuspensions. Les solutions résultantes servirent comme phases dispersées dans des générateurs microfluidiques de gouttelettes à capillaires. Les microgouttelettes de taille contrôlée ainsi produites furent polymérisées en ligne par irradiation UV pour donner lieu à des microsphères ou à des microparticules coeur-écorce composites de polymère toutes deux dopées avec des nanoparticules de polymère. Des microparticles composites et hydrides comportant des nanoparticules d’or dans le coeur et d’argent dans l’écorce furent également obtenues grâce à la réduction photochimique in situ des sels précurseurs lors de la photopolymérisation des microgouttelettes. Ce travail a démontré l’efficacité d’un nouveau dispositif microfluidique basse énergie pour la production de nanoémulsions et leur emploi pour la synthèse de matériaux polymères morphologiquement complexesThe aim of this work was to develop and to study the performances of a low pressure elongational-flow microprocess for the production of size-controlled polymerizable nanoemulsions with narrow size distributions. Nanodroplets diameter was easily tuned in the size range 50-300 nm by varying the process parameters, namely the reciprocating flow rate through the micromixer, the number of cycles and the characteristic dimension of the microchannel. Obtained nanoemulsions were in a second step thermally or UV-assisted polymerized to give colloidal suspensions of size-tunable polymer nanoparticles (87-360 nm). Then, a proper monomer, crosslinker and thermal- or photo-initiator were added to the continuous phase of these nanosupensions. The resulting mixtures were used as the dispersed phases of two different capillaries-based microfluidic droplet generators. The produced sizecontrolled microdroplets were finally UV polymerized online and plain as well as core-shell composite polymeric microparticles doped with lower scale polymer nanoparticles were obtained. Composite/hybrid polymeric core-shell microparticles were also synthesized for which gold nanoparticles in the core and silver nanoparticles in the shell were synthesized in situ from their salt precursors during microdroplets polymerization. This work has demonstrated the high efficiency of a novel low energy microfluidic emulsification device for the production of nanoemulsions which were used for the synthesis of morphologically complex polymeric materials
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El, Kissi Nadia. "Stabilité des écoulements mixtes de polymères fondus : [thèse en partie soutenue sur un ensemble de travaux]." Grenoble INPG, 1989. http://www.theses.fr/1989INPG0046.
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Etude de fluides silicones. Comportement en cisaillement a l'aide d'un rheometre cone-plan ou capillaire. Existence de deux zones de recirculation en amont de la contraction. Localisation du defaut de peau de requin a la sortie des filieres (rupture par fissuration du fluide). Instabilite de l'ecoulement. Etude de la forme des filieres en filage textile
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Hagen, Thomas Ch. "Elongational Flows in Polymer Processing." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/29437.
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The production of long, thin polymeric fibers is a main objective of the textile industry. Melt-spinning is a particularly simple and effective technique. In this work, we shall discuss the equations of melt-spinning in viscous and viscoelastic flow. These quasilinear hyperbolic equations model the uniaxial extension of a fluid thread before its solidification.
We will address the following topics: first we shall prove existence, uniqueness, and regularity of solutions. Our solution strategy will be developed in detail for the viscous case. For non-Newtonian and isothermal flows, we shall outline the general ideas. Our solution technique consists of energy estimates and fixed-point arguments in appropriate Banach spaces. The existence result for a simple transport equation is the key to understanding the quasilinear case. The second issue of this exposition will be the stability of the unforced frost line formation. We will give a rigorous justification that, in the viscous regime, the linearized equations obey the ``Principle of Linear Stability''. As a consequence, we are allowed to relate the stability of the associated strongly continuous semigroup to the numerical resolution of the spectrum of its generator. By using a spectral collocation method, we shall derive numerical results on the eigenvalue distribution, thereby confirming prior results on the stability of the steady-state solution.Ph. D.
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V, Venkataramanan. "Material characterization in elongational flows /." The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487943610784079.
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Souilem, Inès. "Élaboration de miniémulsions dans un nouveau mélangeur à écoulement élongationnel : influence des paramètres du procédé et de la formulation." Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00864095.
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Les mini ou nanoémulsions sont des systèmes fréquemment rencontrés dans différents domaines : cosmétique, pharmaceutique, biomédical... Plusieurs procédés permettent la préparation de nanoémulsions. Cependant, ils présentent tous des limitations en termes de taille des gouttelettes, d'énergie de mélange, de rapport de viscosité entre les phases dispersées et continues, de gamme de pression à appliquer... Ce travail s'intéresse au développement d'un nouveau dispositif basé sur un écoulement élongationnel pour l'élaboration de miniémulsions de monomères. La démarche a consisté d'abord à étudier l'influence des paramètres liés au procédé proprement dit puis à la formulation du système sur la taille des gouttelettes. Cette étude a permis de comprendre les mécanismes mis en jeu lors de la fragmentation des gouttes. Une analyse dimensionnelle a ensuite été développée afin de corréler les tailles obtenues aux paramètres étudiés, par l'utilisation des nombres adimensionnels appropriés. Finalement, des expériences de synthèse en miniémulsion ont été conduites pour tenter de combiner dans le même dispositif les fonctions d'émulsificateur et de réacteur de polymérisation, dans une perspective d'intensification du procédé.
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Rondin, Jérôme. "Apport des écoulements élongationnels lors de la mise en oeuvre de mélanges PP/EPDM réticulés dynamiquement et chargés à base de graphène." Thesis, Strasbourg, 2012. http://www.theses.fr/2012STRAE046/document.
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Le travail de thèse présenté dans ce manuscrit a consisté à mettre en avant un nouveau procédé de mélange des polymères développé au LIPHT lors de la mise en oeuvre de mélanges PP/EPDM réticulés dynamiquement et chargés à base de graphène. Ce nouveau mélangeur, appelé RMX®, se distingue de la plupart des mélangeurs existants par la présence d’écoulements élongationnels forts, la possibilité de mouler directement des éprouvettes à l’issue de l’étape de mélange ainsi qu’une étanchéité aux gaz et aux liquides. Après une optimisation des conditions opératoires de ce mélangeur, nous avons pu évaluer quantitativement l’efficacité du mélange dispersif par analyse numérique de tailles de particules d’EPDM dispersées dans une matrice PP. Le RMX® permet d’obtenir une dispersion fine (~ 1 μm) pour des énergies spécifiques et des temps de mélange inférieurs aux procédés existants. Des tailles significativement réduites ont été obtenues pour des mélanges présentant un rapport de viscosité élevé (p > 1). Ces résultats ont été attribués à la combinaison de taux de déformation en cisaillement élevés dans le canal de l’élément de mélange avec des taux de déformation en élongation majoritaires en entrée/sortie de ce dernier. L’impact des écoulements élongationnels sur l’intervalle de (co)-continuité de mélanges PP/EPDM a ensuite été étudié. Un décalage de la percolation de la phase dispersée (EPDM) vers les hautes concentrations ainsi qu’une borne supérieure de cet intervalle plus élevée ont ainsi pu être mis en évidence à l’aide de techniques complémentaires (MEB, extraction sélective de la phase EPDM, analyse rhéologique). Une procédure originale d’élaboration de matériaux TPV dans le RMX® a également été réalisée. La réticulation dynamique au moyen d’une résine phénolique d’un mélange PP/EPDM présentant une morphologie co-continue a été effectuée. Des taux d’insoluble proche de 100% ainsi que les propriétés élastiques des TPV formés ont permis de confirmer l’efficacité de cette étape de réticulation dans le RMX®. Une dernière étude a consisté à disperser une nanocharge graphitique lamellaire et conductrice (xGNPTM) dans une matrice PP. L’analyse par diffraction des rayons X, les seuils de percolation rhéologique et électrique obtenus autour de 7 et 8 wt% respectivement ainsi qu’un facteur de forme Af ~ 15 suggèrent une absence d’exfoliation ainsi qu’une agrégation importante des particules de xGNPA new mixing device (RMX®) based on elongational flows has been developed during this work. This device has specific technical features comparing to conventional mixers such as: variable mixing volume, direct molding of samples, air and water tightness. After an optimization of processing conditions, dispersive mixing efficiency was assessed on PP/EPDM blends by numerical analysis. Very fine dispersed morphologies were obtained for lower specific mixing energy and mixing times comparing to internal mixer (Haake Rheomix 600). Significantly reduced droplet sizes have been obtained for high-viscosity ratio blends (p > 1). These results indicate an enhanced droplet break-up mechanism in the RMX® which was attributed to the combination of high shear rates inside the mixing element and important elongational flows in the convergent/divergent zones. Impact of elongational flow mixing on the (co)-continuity interval of PP/EPDM blends was investigated. An important shift (~ 10 wt%) of the EPDM percolation threshold as well as a higher phase inversion concentration was observed. A combination of complementary techniques (SEM, selective extraction and rheological analysis) was successfully carried on in order to assess this (co)-continuity interval. Then, PP/EPDM blends with a co-continuous morphology were dynamically crosslinked in the RMX® using resole as a crosslinking agent. An original and specific procedure was developed for this purpose. Gel fraction close to 1 and significantly enhanced elastic properties after crosslinking confirmed the efficiency of this procedure. Finally, the dispersion of lamellar and conductive nanofillers (xGNPTM) in a polypropylene matrix was studied. Microstructural characterization by XRD and optical microscopy, rheological and electrical percolation thresholds (7 and 8 wt% of xGNP respectively) and corresponding aspect ratios (Af ~ 15) have shown no evidence of exfoliation
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Ambari, Abdelhak. "Application des méthodes électrochimiques à l'étude de l'interaction entre l'hydrodynamique et la dynamique des polymères en écoulement élongationnel : interaction entre particules solides en régime de Stokes." Paris 6, 1986. http://www.theses.fr/1986PA066006.
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Dynamique des polymères linéaires et flexibles en écoulement élongationnel. Mise en évidence du changement brutal de la forme pelote à la forme étirée. Deux méthodes de mesure différentes : l'une basée sur la mesure directe de la dissipation viscoélastique, l'autre basée sur les effets de cette transition sur le transfert massique et sur l'hydrodynamique.
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Mestadi, Abdelaziz. "Caractérisation en élongation de polymères fondus et en solution : comparaison entre essais à force constante et à vitesse de déformation constante." Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10079.
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Le rappel des principales techniques de mesure des proprietes elongationnelles des materiaux a l'etat fluide montre que l'essai a force constante convient a la fois aux polymeres fondus et en solution. Ce travail porte sur la comparaison entre essais a force constante et essais a vitesse de deformation constante. Pour analyser l'influence du caractere moleculaire lineaire ou branche sur les mesures envisagees, quatre polybutadienes et deux polydimethylsiloxanes fondus a temperature ambiante sont utilises. La caracterisation rheologique de ces materiaux dans le domaine de la viscoelasticite lineaire permet d'obtenir leur spectre de temps de relaxation a partir des courbes maitresses. La caracterisation dans le domaine non lineaire permet la determination des parametres d'un modele non lineaire integral (modele de wagner). Le modele surestime la rapidite de la relaxation des contraintes aux fortes vitesse de cisaillement. Des essais transitoires en cisaillement et en elongation permettent de definir une mesure de la deformation basee sur un invariant generalise. Les essais a force constante sont analyses a l'aide de ce modele dans un premier temps en supposant la deformation homogene. Ensuite une simulation numerique basee sur la methode des tubes de courant montre que le modele predit correctement le comportement des polymeres lineaires mais pas celui des polymeres branches. Dans une derniere partie la demarche est appliquee a une solution de polyisobutylene proposee dans le cadre d'un programme de recherche international (s1 project)
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Cao, Dongbu. "Modeling of nonisothermal channel flows and elongational flows in polymer processes /." The Ohio State University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=osu148786297213688.
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Gagov, Atanas. "INSTABILITIES IN ELONGATION FLOWS OF POLYMERS AT HIGH DEBORAH NUMBERS." University of Akron / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=akron1191895515.
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Araya, Tadashi. "Grain fabrics formed on horizontal to gently inclined sandy erodible beds under unidirectional, oscillatory and combined flows, with special reference to the dependence of imbrication angles on grain elongation and grain size." 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/147833.
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Chiu, Chih-Wei, and 邱智瑋. "Spinning and Elongational Flow Behaviorof Nanoscale TiO2/PP Fibers." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/38752224919974318854.
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碩士逢甲大學
紡織工程所
92
Nano-scale TiO2/Polypropylene fibers are prepared by melt blending with melt spinning process in this study. The elongational viscosity characteristic of polymer effects by the condition of manufacture, it can be measured in spinning process. The particle size, additive amounts of the nano-scale TiO2 particles are varied, and the temperature, volume flow rate and extracted speed tension are the parameters of this experiment. It is directly measured the diameter, tension, and flow rate of fibers, and calculate apparent elongational viscosity and apparent elongational strain rate by Cogswell’s theory. By the way to obtain the effects while manufacture it. The thermal property are measured by DSC and TGA, and obtained the surface property by AFM. According the relationship of diameter and distance from die are affected by different processes, the diameter of Polypropylene and distance from die of Polypropylene melts will increase with the smaller particles of TiO2, and the diameter and distance from die of Polypropylene melts will increase with additive amounts of the nano-scale TiO2 and volume flow rate increase. The diameter of Polypropylene and distance from die of Polypropylene melts decrease with the increased temperature and extracted speed tension. The elongational viscosity of Polypropylene increases by smaller particle sizes of TiO2.The elongational viscosity of Polypropylene melts increase with additive amounts of the nano-scale TiO2 particles and volume flow rate increase. But the elongational viscosity of Polypropylene melts decrease with the temperature and extracted speed tension increased. The DSC test shows that the melting temperature of Polypropylene fibers doesn’t change. The TGA test shows that the thermal stability properties of nano-scale TiO2/Polypropylene fibers increased. From the observed AFM results, it shows that the surface of Polypropylene fibers covered TiO2 particles, and these particles agglutinated.
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Nieh, Mu-Ping. "Deformation and orientation of dissolved polymer chains in an elongational flow." 1998. https://scholarworks.umass.edu/dissertations/AAI9841901.
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The addition of a low concentration of dissolved high molecular weight polymer can greatly modify the rheological properties of a simple. Many of the modification can be attributed to flow-induced departures of the average chain conformation from its isotropic value at quiescence. The statistical deformation and orientation of polymer chains in flow has been predicted by various molecular models, but these predictions have not been adequately tested. This research provides an important molecular-level understanding of chain conformation in dilute solutions undergoing elongational flow; the work applies light scattering and birefringence techniques to probe chain conformation in situ. We have investigated the influences of chain stiffness and solvent quality on the chain conformations produced in and around the stagnation point of opposed jet flow. By light scattering, the average radius of gyration of the examined polymers has been probed both parallel and perpendicular to the stretching axis for flows of various strength. Flexible polymers are not deformed affinely under any circumstances, with statistical coil deformation falling much below this limit. Although solvent quality has little impact, slightly more coil deformation is observed in a theta solvent than in a good one. For a relatively stiff polymer of approximately 15 persistence lengths, the behavior of chain deformation/orientation in opposed jet flow is different; Because less strain is required to orient a stiff polymer than to deform an analogous flexible polymer, conformation changes are less localized, extending outside the region between the jets. Nevertheless, the overall conformational changes remain less than that predicted by a rod model.
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Tsai, Yu-Tien, and 蔡育田. "Polymer Motion in the Elongation Flow." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/40033991863984626249.
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Borgbjerg, Ulrik. "The recovery of polymer melts after shear and elongational flows." 1994. http://catalog.hathitrust.org/api/volumes/oclc/32776577.html.
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何誌峰. "Studies of the Effect of Elongation Flow on the Dispersive Mixing Elements For the Single Extrusion Process." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/40105228081848925228.
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碩士國立交通大學
應用化學系所
93
Most scholar and experts formerly put forward dispersive mixing element of the curved flight which generate elongation flow as the main research, but not many of them worked out their essays about dispersive mixing element of the flat flank which is without any gap between the flight and the jacket and the changes which are the length of the pin and the amount of the pins in simulation. The goal of my essay is to use finite element method to simulation high molecular polymer flow in the dispersive mixing elements. With changing the configuration of the pins, the gradient of the flight and the distance between two pins along the circumferential direction, making quantitative analyses. Moreover, the strain rate, interfacial area ratio and energy consumption are employed to indicate the mixing effect.