• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 23
  • 22
  • 11
  • 9
  • 7
  • 4
  • 3
  • 1
  • 1
  • 1
  • Tagged with
  • 97
  • 8
  • 8
  • 7
  • 7
  • 6
  • 6
  • 5
  • 5
  • 5
  • 5
  • 5
  • 5
  • 4
  • 4
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Mécanismes moléculaires impliqués dans la liaison des +TIPs aux microtubules / Molecular mechanisms involved in the interaction between +TIPs and microtubules

Guesdon, Audrey 20 June 2013 (has links)
Les microtubules (MTs) sont des constituants hautement dynamiques du cytosquelette, impliqués dans de nombreux processus cellulaires tels que la division cellulaire ou le transport d'organites. Leur comportement dynamique est régulé par différents facteurs tels que les +TIPs, qui présentent la particularité de cibler les extrémités en croissance des MTs. Une de ces protéines, EB1, cible de façon autonome ces extrémités et y recrute un grand nombre d'autres +TIPs. Néanmoins, les mécanismes moléculaires impliqués dans cette reconnaissance restent imprécis. Afin de mettre en évidence une caractéristique structurale présente à l'extrémité des MTs en croissance et préférentiellement reconnue par EB1, nous avons utilisé deux approches de cryo-microscopie électronique. Nous avons tout d'abord utilisé une approche d'analyse par particules isolées, dans le but de comparer les reconstructions 3D de MTs assemblés en présence de GTP ou de GMPCPP, analogue lentement hydrolysable du GTP. Par la suite, nous avons utilisé la cryo-tomographie électronique couplée au marquage d'EB1 avec des nanoparticules d'or fonctionnalisées. Nos résultats nous permettent de proposer un modèle de ciblage impliquant une relocalisation de l'extrémité C-terminale d'EB1 lors de la fermeture des feuillets en tube. Cette relocalisation permettrait de recruter les autres +TIPs, et entraînerait une perte d'affinité d'EB1 pour la paroi des microtubules. La comparaison de ces résultats avec des études récentes effectuées par d'autres équipes, et concernant le rôle de l'hydrolyse du GTP dans la liaison d'EB1 avec les MTs, nous permet de proposer un modèle global incluant l'ensemble de ces données. / Microtubules (MTs) are highly dynamic cytoskeleton polymers, involved in many cellular processes, including cell division and intracellular transport. Their dynamic behavior is regulated by numerous factors, such as +TIPs that preferentially target MT growing ends.
22

Life threatening GI bleeding from stomal varices managed by TIPS and Amplatzer plug embolization

Wilhoite, David, Aasen, Tyler, D.O., Schmidt, Lawrence, M.D. 05 April 2018 (has links)
Stomal varices are a rare phenomenon that can infrequently develop in patients with enterostomies and portal hypertension. Acute gastrointestinal bleeding from stomal varices can be life threatening and is often a diagnostic challenge. We present a case of severe gastrointestinal hemorrhage from stomal varices requiring emergent intervention with transjugular intrahepatic portosystemic shunt (TIPS) and plug embolization. A 61 year old male patient with a history of colorectal adenocarcinoma status post chemotherapy, radiation, along with low anterior colon resection with ostomy creation presented with a one day history of sudden onset of bright red blood from his colostomy site. He had a known history of decompensated cirrhosis related to hepatitis C and alcohol abuse. On arrival, the patient was tachycardic with borderline low blood pressure with evidence of bright red bleeding from his ostomy site. After initial resuscitation, a colonoscopy through the stoma revealed active bleeding from what appeared to be submucosal colonic varices. The patient continued to experience large volumes of blood loss and became more hemodynamically unstable. Cross sectional imaging showed colonic varices being fed by a branch of the inferior mesenteric vein. The patient underwent TIPS followed by Amplatzer plug embolization of the branch of the interior mesenteric vein that was feeding the colonic stomal varices. The patient’s bleeding was stopped by the combination of these therapeutic modalities and he recovered without complication. The current standard of care for treatment of such varices is with either (1) local therapy with ligation or sclerotherapy, (2) surgical interventions such as stomal manipulation or vessel shunting, either transhepatic or portosystemic to reduce portal pressures, or (3) liver transplantation. Our patient required an unusual combination of TIPS and Amplatzer plug embolization to control his massive hemorrhage. This combination of therapies has been shown effective for the management of select cases of esophageal or gastric variceal bleeding; however, our case demonstrates that the application of the TIPS plus Amplatzer plug embolization can be applied more broadly to the rare scenario of colonic stomal varices.
23

Examination of the Informed Consent Process as Experienced by Patients Who Underwent a De Novo Transjugular Intrahepatic Portosystemic Shunt, Chemoembolization or Radioembolization Procedure

Hughes-Gay, Marsha A. 08 1900 (has links)
Indiana University-Purdue University Indianapolis (IUPUI) / The purpose of this study is to examine the informed consent (IC) procedure as it was experienced by patients who had undergone a de novo transjugular intrahepatic portosystemic shunt (TIPS), chemoembolization (TACE), or radioembolization (TARE) procedure in an Interventional Radiology (IR) Department. The three main study aims and a fourth exploratory aim are as follows: (1) Describe how patients who underwent a de novo TIPS, TACE, or TARE procedure in an IR Department described the IC procedure; (2) Describe what information patients who underwent a de novo TIPS, TACE, or TARE procedure in an IR Department recalled being told during the IC procedure; (3) Describe the satisfaction of patients who underwent a de novo TIPS, TACE, or TARE procedure in an IR Department with the IC procedure; and (4) Explore how the IC experiences of patients who underwent a de novo TIPS, TACE, or TARE procedure in an IR Department differed according to their levels of health literacy. Using a qualitative descriptive design, participants were recruited from an IR department that performed these procedures. A total of 14 participants were interviewed about their IC experiences and the Newest Vital Sign (NVS) Health Literacy assessment was administered. The participants described the IC procedure by discussing the staff they encountered, their feelings during the visit, the support persons who accompanied them, and the decisions they made about the procedure. The participants recalled being told about how their procedure would be performed, the care they would need, and the benefits and risks of the procedure. Most were satisfied with the information received during the IC procedure and found the information consistent with how they experienced the procedure. A few participants would have liked more visual materials, addition details about the procedure, simpler language, or more explanation of the medical terminology. No apparent differences in the IC experience could be attributed to health literacy. These findings suggest that persons’ experiences during the IC process are multi-faceted and affected by their emotions and concerns and the nature of their encounters with their healthcare providers.
24

Low-Speed Aerodynamic Characteristics of a Delta Wing with Deflected Wing Tips

Trussa, Colin Weidner 08 October 2020 (has links)
No description available.
25

Dynamic Modeling of a Supersonic Tailless Aircraft with All-moving Wingtip Control Effectors

White, Brady Alexander 19 December 2007 (has links)
A six degree-of-freedom model for a tailless supersonic aircraft (TSA) concept was developed using MATLAB and Simulink. Aerodynamic data was provided through the computational fluid dynamics analysis of Techsburg, Inc. A three degree-of-freedom model of the configuration's longitudinal dynamics was completed first. Elevator control power was derived from the dynamic response requirements for pitch chosen by Techsburg. The propulsion model utilized General Electric F-414-400-like turbofan engines because an engine deck was readily available. Work on the six degree-of-freedom dynamic model began with determining the necessary rolling and yawing moment coefficients necessary to meet the rest of the chosen dynamic response requirements. These coefficients were then used to find the corresponding all-moving tip deflections. The CFD data showed that even at small all-moving tip deflections the rolling moment coefficient produced was much greater than the amount of yawing moment coefficient produced. This result showed that an additional roll effector was needed to counteract excess rolling moment at any given all-moving tip deflection and trim the aircraft. An angle of attack and pitch rate feedback controller was used to improve the longitudinal dynamics of the aircraft. Because this configuration lacked a vertical tail, a lateral-directional stability augmentation system was vital to its success. The lateral-directional dynamics were improved to Level 1 flying qualities through use of a modified roll/yaw damper. The modified controller fed yaw rate back to both the all-moving tips and roll effector. The six degree-of-freedom model was augmented with actuator dynamics for the elevator, roll effector, and all-moving tips. The actuators were modeled as first order lags. The all-moving tip actuator time constant was varied to determine the effect of actuator bandwidth on the lateral-directional flying qualities. After the actuator dynamics were successfully implemented, the six degree-of-freedom model was trimmed for both standard cruise and engine-out situations. The eccentuator concept from the DARPA Smart Wing program was selected as a possible conceptual design for the all-moving tip actuation system. The success of the TSA six degree-of-freedom dynamic model proved that morphing all-moving tips were capable of serving as effective control surfaces for a supersonic tailless aircraft. / Master of Science
26

Playful Preschool STEM: Three Tips to Support Young Learners Every Day

Lange, Alissa A. 15 September 2020 (has links)
No description available.
27

Shunt portosystémique par échoendoscopie sur modèle animal / Portsystemic Shunt by Endoscopic Ultrasonography on an Animal Model

Poincloux, Laurent 04 April 2016 (has links)
L’échoendoscopie thérapeutique occupe une place croissante et incontournable de l’activité médico-chirurgicale en pathologie digestive depuis le développement des sondes sectorielles. Les domaines d’application de cette technique interventionnelle mini-invasive sont de plus en plus nombreux, d’une part en pathologie biliopancréatique et entérale permettant la réalisation d’anastomoses évitant un recours à la chirurgie traditionnelle, et d’autre part en cancérologie digestive car elle permet de délivrer un agent thérapeutique, une source de rayonnement ou des cellules liées au système immunitaire dans une lésion ciblée. L’abord vasculaire est une voie récente et prometteuse de l’échoendoscopie interventionnelle offrant des perspectives thérapeutiques en hépatologie notamment dans le domaine de l’hypertension portale. Ce travail se décompose en trois parties décrivant successivement l’état de l'art des applications de l’échoendoscopie interventionnelle, puis deux travaux originaux expérimentaux : dans un premier temps, le transfert de la technique d’anastomose biliodigestive (réalisée régulièrement dans notre centre) à l’abord vasculaire portosystémique sur animal sain, puis dans un deuxième temps la validité de la technique sur modèle animal de fibrose hépatique. La première série d’expérimentations a permis de mettre au point la technique de création d’un shunt intrahépatique portosystémique par échoendoscopie chez 23 cochons sains, en collaboration avec l’équipe de radiologie vasculaire. Ces procédures ont été réalisées dans une salle de cathétérisme vasculaire expérimentale (laboratoire Caviti) dans le cadre du laboratoire d’accueil ISIT (Image Science for Interventional Techniques, Pr. L. Boyer, Pr. J.-Y. Boire, UMR CNRS/UDA 6284). Les résultats ont été concluants puisque le shunt est apparu faisable dans 91% des cas, fonctionnel dans 81% des cas avec une morbidité de 14,2%. La deuxième série d’expérimentations a permis de valider cette technique d’échoendoscopie chez un modèle porcin de fibrose hépatique par embolisation radiologique, en collaboration avec l’Institut National de Recherche Agroalimentaire de Theix pour la stabulation des animaux. Ce travail multidisciplinaire a permis une collaboration étroite entre endoscopistes, radiologues, chirurgiens viscéraux et anatomopathologistes, s’inscrivant dans une démarche de recherche transversale. Les résultats sont encourageants puisqu’un shunt intrahépatique porto-systémique par échoendoscopie s’est révélé techniquement faisable et fonctionnel sur modèle de fibrose hépatique avec une survie à 7 jours des animaux dans deux tiers des cas. Avant d’envisager une étude princeps chez l’homme, des études complémentaires sont néanmoins nécessaires sur des modèles porcins présentant une fibrose hépatique associée à une hypertension portale en augmentant la durée de stabulation, en homogénéisant la procédure de squelettisation de l’artère hépatique et en adaptant la dose de solution injectée. Cette technique pourrait constituer à terme une alternative en cas d’échec de la technique standard pour complications de l’hypertension portale (shunt intrahépatique portosystémique par voie transjugulaire) chez des patients alors en situation d’impasse thérapeutique. / Therapeutic endoscopic ultrasonography is a growing and essential part of the medical and surgical activity in digestive pathology since the development of sectoral probes. The fields of application of this minimally invasive interventional technique are more and more numerous, on the one hand in biliopancreatic and enteral pathology, allowing the realization of anastomoses without traditional surgery, and on the other hand in digestive oncology, because it makes it possible to deliver a therapeutic agent, a source of radiation or cells linked to the immune system in a targeted lesion. The vascular approach is a recent and promising way of interventional endoscopic ultrasound offering therapeutic perspectives in hepatology, especially in the field of portal hypertension.This work is divided into three parts successively describing the state of the art of the applications of interventional ultrasonoscopy, then two original experimental works: initially, the transfer of the technique of biliodigestive anastomosis (performed regularly in our center ) at the portosystemic vascular approach on healthy animal, then in a second time the validity of the animal model technique of liver fibrosis.The first series of experiments led to the development of the technique for the creation of an intrahepatic shunt portosystemic by echoendoscopy in 23 healthy pigs, in collaboration with the vascular radiology team. These procedures were performed in an experimental vascular catheterization room (Caviti laboratory) as part of the ISIT host laboratory (Image Science for Interventional Techniques, Prof. L. Boyer, Pr. J.-Y.Boire, UMR CNRS / UDA 6284). The results were conclusive since the shunt appeared feasible in 91% of cases, functional in 81% of cases with a morbidity of 14.2%. The second series of experiments validated this endoscopic ultrasound technique in a porcine model of liver fibrosis by X-ray embolization, in collaboration with Theix National Institute for Food Research for Animal Stabling. This multidisciplinary work has allowed close collaboration between endoscopists, radiologists, visceral surgeons and anatomopathologists, as part of a transversal research approach. The results are encouraging since a porto-systemic intrahepatic shunt by endoscopic ultrasonography proved to be technically feasible and functional on a hepatic fibrosis model with a 7-day survival of the animals in two-thirds of the cases. Before considering a primary study in humans, additional studies are nevertheless necessary on porcine models presenting hepatic fibrosis associated with portal hypertension by increasing the duration of stabulation, by homogenizing the procedure of skeletonization of the hepatic artery and by adjusting the dose of injected solution. This technique could eventually be an alternative in case of failure of the standard technique for complications of portal hypertension (intrahepatic portosystemic shunt transjugular) in patients then in a situation of therapeutic impasse.
28

Verbesserung des Ernährungszustands bei Patienten mit Leberzirrhose nach Implantation eines transjugulären intrahepatischen portosystemischen Stent-Shunts (TIPS)

Gebhardt, Deborah Patricia 24 November 2000 (has links)
Bei 22 Patienten mit Leberzirrhose wurde prospektiv der Ernährungszustand mit seinen Komponenten Energieverbrauch, Nahrungsaufnahme und Körperzusammensetzung sowohl vor Anlage eines TIPS, als auch 1, 6 und 12 Monate nach TIPS-Implantation untersucht und in Beziehung zu Daten gesunder Probanden gesetzt. Im Vergleich zu gesunden Kontrollpersonen waren bei Patienten vor TIPS-Anlage Körpergewicht und body-mass-index nicht vermindert, während Muskel- und Körperzellmasse (BCM) reduziert waren. Im Grundumsatz (REE) bestand kein Unterschied zu Kontrollen, wenn der gesamte Grundumsatz betrachtet wird. Dagegen war der spezifische, auf die Körperzellmasse bezogene Grundumsatz (REE/BCM) bei Patienten signifikant erhöht. Patienten wiesen also gegenüber Kontrollen einen hypermetabolen Status auf. Die Substratoxidation der Patienten war durch eine bevorzugte Verwendung von Lipiden gekennzeichnet. Nach TIPS-Anlage nahmen Körpergewicht und BMI der Patienten zu aufgrund einer Verbesserung in der Körperzusammensetzung mit signifikantem Anstieg von Muskelmasse, Körperzellmasse und dem Quotienten von Körperzellmasse und Körpermasse. Darüberhinaus war eine signifikante Abnahme der Aszitesmenge zu verzeichnen. Die Fettmasse blieb trotz Zunahme der Körpermasse unverändert. Entsprechend der Zunahme der Körpermasse stieg der Grundumsatz nach TIPS-Anlage signifikant an, die Betrachtung des spezifischen Energieumsatzes zeigte jedoch eine abnehmende Tendenz im Sinne einer Normalisierung des bei Zirrhosepatienten gegenüber Kontrollen erhöhten Energieumsatzes. Dieser Abnahme des spezifischen Energieverbrauchs stand eine zunehmende Nährstoffaufnahme gegenüber, so daß diese Verbesserung der Energiebilanz als eine der Ursachen für die Verbesserung des Ernährungzustandes zu sehen ist. Unbeeinflußt von der TIPS-Anlage blieb die Bevorzugung von Fett als oxidativem Substrat. Bezüglich der Organfunktionen war nach TIPS-Anlage eine partielle Verminderung der hepatischen Syntheseleistung (Quick, nicht aber Albumin) und eine signifikante Verbesserung der Nierenfunktion und psychometrisch gemessenen hirnorganischen Leistungsfähigkeit zu beobachten. Die Anlage und Funktionserhaltung eines TIPS war bei Patienten mit Leberzirrhose mit einer bedeutsamen Verbesserung des Ernährungszustandes und insbesondere des prognostisch relevanten Kompartiments Körperzellmasse und Muskelmasse verbunden. Bei unveränderten Ernährungsempfehlungen waren die Patienten in höherem Maße in der Lage, diese Empfehlungen zu realisieren und insbesondere eine höhere Eiweißmenge ohne Verschlechterung der Enzephalopathie zuzuführen. Welchen Einfluß die einzelnen Faktoren wie verminderte Aszitesmenge, Verbesserung der intestinalen Absorption oder Vermeidung erneuter kataboler Situationen (gastrointestinale Blutungen, Parazentese und Endotoxinämie durch Reduktion der portalen Hypertension) an diesem Ergebnis haben, muß durch weitere Untersuchungen geklärt werden. / 22 patients with liver cirrhosis were examined prospectively regarding their nutritional state and its components energy expenditure, energy intake and body composition before and 1, 6 and 12 months after implantation of a transjugular intrahepatic portosystemic stent - shunt (TIPS). These data were compared to those corresponding of a group of healthy control subjects. Compared to these healthy individuals body weigth and body mass index (BMI) of the patients were not reduced while muscle mass and body cell mass (BCM) were impaired before TIPS-implantation. There was no difference in resting energy expenditure (REE) between both groups. The ratio REE/BCM is called specific resting energy expenditure. This ratio was found to be increased in the patient group which means that patients were hypermetabolic when compared to controls. Lipids turned out to be the prefered fuel in patients. After TIPS-insertion body weight and BMI increased in patients because muscle mass, BCM and BCM/body weight all increased significantly in the patient group. Meanwhile the amount of ascites was reduced significantly. Fat mass remained stable after TIPS. Because of this increase of body weight energy expenditure had to increase, too. On the contrary, the specific REE showed a decrease which means normalization of the pathological high results of this parameter. A decrease in specific REE and an increase in energiy intake lead to an improvement of energy balance. This is probably one min cause of the improvement in the nutritional state of the patients after TIPS. After TIPS lipids remained to be the main source of substrate for oxidation. Partly, the synthetical function of the liver was impaired after TIPS (thromboplastin time, but not Albumin) while renal function and mental performance measured by psychometric tests improved significantly. The implantation of TIPS and surveillance of its function in patients with liver cirrhosis was accompanied by an improvement of their nutritional state. Even more important, there was an improvement of body cell mass and of muscle mass which both are of significantly prognostic value in this kind of patients. Dietary recommendations were not changed after TIPS but patients were able to realize them in a better way and they tolerated an increased intake of protein without an increase in the rate of hepatic encephalopathy. Furthe studies will have to be performed in order to find out the influences of different factors as reduced amount of ascites, improvement of intestinal absorption or avoiding of catabolic periods (gastrointestinal bleeding, paracentesis and endotoxinaemia by reduction of portal hypertension).
29

Comportamento de fases de soluções binarias e ternarias de poli(etileno-co-alcool vinilico), poli(metacrilato de metila) e dimetilformamida / Phase behavior of binary and ternary solutions of poly(ethylene-co-vinyl alcohol), poly(methyl methacrylate) and dimethylformamide

Lima, Juliana Aristeia de 11 June 2008 (has links)
Orientador: Maria Isabel Felisberti / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-12T12:37:28Z (GMT). No. of bitstreams: 1 Lima_JulianaAristeiade_D.pdf: 4425741 bytes, checksum: e0c47d6335f66cc31a0fe6e5ac1c0457 (MD5) Previous issue date: 2008 / Resumo: Neste trabalho foram estudadas blendas de poli(etileno-co-álcool vinílico) (EVOH), um copolímero semicristalino que combina segmentos hidrofílicos e hidrofóbicos e poli(metacrilato de metila) (PMMA), um polímero amorfo e hidrofílico. As blendas de EVOH, com teor de etileno variando de 27 a 44 mol %, e PMMA foram preparadas por casting a partir de soluções em DMF, e por mistura mecânica em um mini-misturador, objetivando: i) avaliar o comportamento de fases e a morfologia das blendas, EVOH/PMMA, em função da composição das misturas, do teor de etileno nos copolímeros de EVOH e do método de preparação; ii) obter os diagramas de fases das soluções binárias, EVOH/DMF, e ternárias, EVOH/PMMA/DMF, através do processo de separação de fases induzido termicamente (TIPS). O comportamento de fases das blendas, EVOH/PMMA, foi estudado através de Calorimetria Diferencial de Varredura (DSC) e Análise Dinâmico-Mecânica (DMA). A morfologia das blendas foi investigada por Microscopia Eletrônica de Varredura (SEM). As blendas independentemente do modo de preparação e da composição são imiscíveis. Como conseqüência desta imiscibilidade, as temperaturas de fusão (Tf) e cristalização (Tc) não são afetadas pela presença de PMMA. A morfologia das blendas varia com a composição e método de preparação. As blendas obtidas pelo método mecânico são compactas, apresentando morfologia de fase dispersa em uma matriz, com inversão de fases em aproximadamente 50 % em massa de cada componente. As soluções binárias, EVOH/DMF, e ternárias, EVOH/PMMA/DMF, foram submetidas a ensaios para a determinação das temperaturas de turvamento (Tturv) por microscopia ótica, e de cristalização dinâmica (Tcd), por DSC. As soluções binárias apresentaram comportamento UCST (upper critical solution temperature), sendo que a separação de fases L-L ocorre a temperaturas superiores à separação de fases S-L. O modelo de interações binárias prevê que a curva de separação L-L para as soluções EVOH- 38/DMF esteja situada a temperaturas superiores em relação às soluções EVOH-32/DMF e indica que a separação de fases resulta da baixa afinidade entre segmentos hidrofóbicos do EVOH com os segmentos do polímero contendo hidroxila e com o solvente, DMF, concordando com os dados obtidos experimentalmente. Filmes de EVOH obtidos pela evaporação do solvente mostraram-se densos, sem a presença de poros. As soluções ternárias também apresentaram comportamento UCST, resultando em duas fases macroscópicas, F1 e F2, à temperatura ambiente. A composição destas fases foi determinada por Análise Termogravimétrica (TGA), e os resultados mostraram que uma das fases macroscópicas é rica em EVOH e outra fase é rica em PMMA. As blendas resultantes da secagem dos sistemas ternários apresentaram duas camadas: uma densa e rica em PMMA e outra porosa e rica em EVOH. A presença de PMMA foi decisiva à formação de estruturas porosas / Abstract: In this work blends of poly (ethylene-co-vinyl alcohol) (EVOH), a semicrystalline copolymer which combines hydrophobic and hydrophilic segments and poly (methyl methacrylate) (PMMA), an amorphous and hydrophilic polymer were studied. EVOH blends, with ethylene content ranging from 27 to 44 mol% and PMMA were prepared by casting from solutions in DMF, and by mixing into a mini-mixer, with the objective of: i) evaluate the phase behavior and the morphology of the blends, EVOH/PMMA, depending on the composition of mixtures, the ethylene contents in the copolymers of EVOH and the conditions of mixing; ii) obtain the phase diagrams of the binary and ternary solutions, EVOH/DMF and EVOH/PMMA/DMF, respectively, by the process of thermally induced phase separation (TIPS). The phase behavior of the blends, EVOH / PMMA, was investigated by Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA). The morphology of the blends was investigated by Scanning Electron Microscopy (SEM). The blends independently of the method of preparation and of the composition are immiscible. As a result of immiscibility, the melting temperature (Tm) and the crystallization temperature (Tc) are not affected by the presence of PMMA. The morphology of the blends varies with the composition and with the method of preparation. The blends produced by the mechanical method is compact, showing morphology of dispersed phase in a matrix, with inversion of phases in about 50% by weight of each component. The binary solutions, EVOH-38/DMF and EVOH-32/DMF, were submitted to experiments to determine the cloud temperature (Tcloud) by optical microscopy, and the dynamic crystallization (Tcd), by DSC. The binary solutions show UCST behavior (upper critical solution temperature), and the L-L phase separation occurs at higher temperatures than the S-L phase separation. The binary interaction model provides the L-L line to the EVOH-38/DMF, solutions which was situated at higher temperatures than the EVOH-32/DMF solutions and indicates that the phase separation results from the low affinity between the hydrophobic segments of EVOH with the segments of the polymer containing hydroxyl and the solvent, DMF, which agrees with the data obtained experimentally. Films of EVOH obtained by the solvent evaporating seemed to be dense, without the presence of pores. The ternary solutions also had UCST behavior, resulting in two macroscopic phases, F1 and F2, at room temperature. The phase compositions were determined by Thermogravimetric Analysis (TGA), and the results showed that one of the macroscopic phases is rich in EVOH and the other phase is rich in PMMA. The blends resulting from drying of ternary systems had two layers: a dense and rich in PMMA and another porous and rich in EVOH. The presence of PMMA was crucial to the formation of porous structures / Doutorado / Físico-Química / Doutor em Ciências
30

Comportamento de fases de soluções de poliolefinas funcionalizadas e implicação na obtenção de membranas pelo processo TIPS / Phase behavior of functionalized polyolefin solutions and its inference on obtaining membrane by TIPS process

Marques, Rosalva dos Santos 12 September 2014 (has links)
Orientador: Maria Isabel Felisberti / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-26T22:37:44Z (GMT). No. of bitstreams: 1 Marques_RosalvadosSantos_D.pdf: 38406911 bytes, checksum: 574d251b2b2578b4a3d9fd0b4e82fcf7 (MD5) Previous issue date: 2014 / Resumo: Neste trabalho, estudou-se o comportamento de fases de soluções binárias e ternárias de poliolefinas funcionalizadas com hidroxilas (EVOH) e ácido carboxílico (PEAA) nos solventes dimetilformamida e álcool benzílico. Utilizou-se EVOH contendo 27 e 44 mol % e PEAA contendo 80 mol % de etileno. As soluções exibem o comportamento de fases do tipo UCST, apresentando separações de fases líquido-líquido (L-L) e sólido-líquido (S-L). As temperaturas de separação de fases L-L e S-L, TL-L e TS-L, respectivamente, foram determinadas para soluções com diferentes composições por inspeção visual e por DSC, respectivamente. Enquanto TS-L para as soluções binárias de EVOH varia fortemente da com a composição das soluções binárias, TS-L para as soluções binárias de PEAA é praticamente constante. Estes resultados foram interpretados sob a ótica de um modelo em que a cristalização do PEAA, que envolve os segmentos de etileno do copolímero, ocorre quase na ausência de solvente. Já a cristalização do EVOH, que envolve os segmentos hidroxilados, ocorre em meio ao solvente, em uma condição em que o potencial químico do polímero varia com a composição da solução. Este modelo pode ser comprovado por estudos de fluorescência empregando-se o pireno e o acetato de uranila como sondas hidrofóbica e hidrofílica, respectivamente. Estes estudos de fluorescência permitiram também acessar transições não detectáveis por DSC. As soluções ternárias homogêneas apresentam mais de uma separação de fases L-L quando submetidas a resfriamento. O diagrama de fases ternário foi construído determinando-se as composições das soluções em equilíbrio, decorrentes da primeira separação de fases L-L, por termogravimetria de alta resolução. Os diagramas de fases das soluções ternárias resultantes das combinações possíveis entre os diferentes polímeros e solventes apresentam regiões de miscibilidade limitadas localizadas em regiões próximas aos vértices, sendo as composições das fases em equilíbrio características de cada combinação nas soluções ternárias. Os materiais resultantes da evaporação do solvente de soluções submetidas ao processo TIPS (Temperature Induced Phase Separation) são compactos ou porosos, dependendo da afinidade polímero-solvente. Entretanto, as morfologias dos materiais resultantes de soluções ternárias submetidas ao processo TIPS são únicas e características do par polímero-polímero, demonstrando que a estratégia de combinação de polímeros para controlar a morfologia é viável / Abstract: The phase behavior of binary and ternary solutions of functionalized poliolefins with hydroxyls (EVOH) and carboxylic acid (PEAA) were studied using dimethylformamide and benzyl alcohol as solvents. PEAA containing 80 mol % and EVOH containing 27 and 44 mol % of ethylene were used. The binary and ternary solutions present a typical UCST behavior associated to liquid-liquid (L-L) and solid-liquid (S-L) phase separation. The temperatures related to L-L and S-L phase separation, TL-L e TS-L, respectively, were determined visually and using DSC, respectively. While TS-L depends on the EVOH solution composition, it is practically constant for PEAA solutions. These results were explained using a model in which the crystallization of PEAA from the solution occurs in absence of solvent, once it involves the polyethylene segments. On the contrary, the crystallization of EVOH from the solution, that involves the hydroxylated segments, occurs in presence of the solvent. This condition leads to the decrease of the chemical potential of EVOH in the solution. The models could be proved by fluorescence experiments using pyrene and uranyl acetate as hydrophobic and hydrophilic probes, respectively. Moreover, the fluorescence experiments allow accessing other transitions not detectable by DSC for ternary solutions. The homogeneous ternary solutions present more than one L-L phase separation by cooling. The ternary diagram was determined by the first L-L phase separation using the composition data accessed by high resolution thermogravimetry. The ternary solutions of all possible combination of polymers and solvents show a restricted miscibility window in the regions near the vertices. The composition of the phases in equilibrium is characteristic of each ternary solution, as well as, the morphology of the materials resulting from the evaporation of the solvent after the solution being subjected to TIPS (Temperature Induced Phase Separation) process. This process applied to binary and ternary solutions resulted in dense or porous materials depending on the polymer-solvent affinity. However, the morphology resulting from ternary solutions subjected to TIPS process and solvent evaporation is unique, showing that the strategy of combining different polymers is a viable route to control the morphology of polymers / Doutorado / Físico-Química / Doutora em Ciências

Page generated in 0.0394 seconds