Analysis of the electronic structures of nitrogen-doped, amorphous carbon samples and of nanodiamond films are carried out in order to determine their sp2 bonding concentration. The amorphous carbon samples under consideration are deposited onto polytetrafluoroethylene (PTFE) polymer substrates by hot wire plasma sputtering of graphite in varying nitrogen concentration atmospheres. The deposition or modification of the substrates surface may lend itself to increasing hardness and wear resistance. Eventually these polymer substrates may be used for applications in the field of biomaterials, focusing on cardiovascular surgery, where a low blood/surface interaction is important. The primary technique used in this study is x-ray absorption spectroscopy, measured at the Advanced Light Source synchrotron at the Lawrence Berkeley National Laboratory, Berkeley, USA. A method of analyzing these spectra was then developed to determine the sp2 bonding concentrations in carbon films. Through this newly developed analysis method, the sp2 bonding concentrations in these samples increases from 74 to 93% with growing nitrogen doping. The diamond films presented here are deposited on silicon wafer substrates in a methane atmosphere by microwave plasma deposition. Various deposition conditions, such as bias voltage and methane atmosphere concentration, affect the purity of the diamond film. This analysis reveals sp2 bonding concentrations in these samples from, typically, a few percent to 25%.

A clutch actuator is used in a vehicle to transmit movement and force from the clutch pedal to the release bearing of the clutch. A pneumatic clutch actuator consists of an anodised aluminium cylinder, inside of which a piston, with a rubber lip seal and a PTFE guiding ring, slides. The system is lubricated with silicone grease before assembly. A commercial clutch actuator of this type, has a service life of 3 million actuations and must function in a wide temperature range, from -40 ºC to 140 ºC. In this thesis, the complex tribological system of pneumatic clutch actuators has been studied. Field worn actuators have been disassembled and investigated. A laboratory test method has been developed to understand the tribomechanisms present in pneumatic clutch actuators. The test method's capability of simulating the real contact has been verified, by the comparison with studied actuators from the field. The influence of contact parameters: temperature, load, lubrication and particle contamination, has been investigated. In addition, different anodised aluminium surfaces have been studied. The manufacturing method of the aluminium cylinder influences surface topography and structure of the oxide, resulting in different mechanical and frictional properties. The wear during tests with only silicone grease is reminiscent, but on a lower scale, to the wear during tests with a mixture of silicone grease and standard dust. The initially applied amount of silicone grease is not important, the friction seems to depend on the amount of silicone grease that is dragged into or pushed out from the contact area during testing. Silicone grease lubrication reduces wear of the lip seal. However, during some tests, an adhesive layer, composed of  grease residuals and some PTFE, was formed on the lip. A triple PTFE transfer, from guiding ring to aluminium surface, to lip seal, to aluminium surface, occurred. Such transfer of material from the PTFE guiding ring was detected from the unlubricated tests, and also from the silicone grease lubricated tests, i.e. silicone grease lubrication does not prevent PTFE material transfer.

Analysis of the electronic structures of nitrogen-doped, amorphous carbon samples and of nanodiamond films are carried out in order to determine their sp2 bonding concentration. The amorphous carbon samples under consideration are deposited onto polytetrafluoroethylene (PTFE) polymer substrates by hot wire plasma sputtering of graphite in varying nitrogen concentration atmospheres. The deposition or modification of the substrates surface may lend itself to increasing hardness and wear resistance. Eventually these polymer substrates may be used for applications in the field of biomaterials, focusing on cardiovascular surgery, where a low blood/surface interaction is important. The primary technique used in this study is x-ray absorption spectroscopy, measured at the Advanced Light Source synchrotron at the Lawrence Berkeley National Laboratory, Berkeley, USA. A method of analyzing these spectra was then developed to determine the sp2 bonding concentrations in carbon films. Through this newly developed analysis method, the sp2 bonding concentrations in these samples increases from 74 to 93% with growing nitrogen doping. The diamond films presented here are deposited on silicon wafer substrates in a methane atmosphere by microwave plasma deposition. Various deposition conditions, such as bias voltage and methane atmosphere concentration, affect the purity of the diamond film. This analysis reveals sp2 bonding concentrations in these samples from, typically, a few percent to 25%.

The heart is one of the most important organs of the human body and cardiovascular diseases remain the biggest cause of deaths worldwide. Today, due to the aging of the population and the growing demand for cardiovascular implants, improving the performance of artificial surfaces of vascular prostheses is highly desired. The common material for fabricating prostheses, such as stents used to remedy narrow and weak arteries, is Fluorocarbon polymers or expanded Polytetrafluoroethylene (ePTFE, Gore-tex). Although these polymers are well known for chemical inertness, thermal stability and low friction, they can cause early thrombosis (forming clot) and coagulation in blood vessels and require periodic replacement. Modifying the surface properties of Polytetrafluoroethylene (PTFE) by coating with carbon-based materials may improve its blood compatibility. Carbon-based coatings have properties similar to biomedical components, such as low friction, bioinertness, high wear resistance and exceptional hardness. Plasma processing methods are commonly used for coating thin films on various materials including carbon-based components. Plasma-based processes are also widely used in the aerospace, automotive, steel and biomedical industries. For example, extending the lifetime of surgically implanted hip joints and cutting tools are biomedical and industrial applications of plasma-based material processing respectively. Plasma-assisted deposition techniques are commonly used for carbon-based coating including nitrogen-doped amorphous carbon (a-C) films. In this thesis, PTFE samples with different thickness and roughness characteristics are used as substrates and diamond-like carbon (DLC) is deposited on them by simultaneous plasma-assisted sputtering and chemical vapour deposition (CVD). Hot filament plasma and ICP (Inductively coupling plasma) are used to coat DLC on PTFE and silicon (Si) substrates under various plasma conditions. The latter is the first report on the techniques to coat DLC by ICP plasma sputtering. This new technique (ICP-sputtering) is developed to improve low deposition rate and high temperature deposition of previous method (Hot filament plasma sputtering). Advantageous of this new developed method (ICP-sputtering) are discussed and compared with the previous method in this thesis. Various amount of nitrogen is introduced to the plasma chambers and the effect of nitrogen dopant is also studied using different characterization techniques for chemical, electronic and morphological properties of coated films. sp2 and sp3 contents were also estimated in amorphous carbon (a-C) and nitrogenated amorphous carbon (a-CN) films. Characterization techniques used for in this thesis are including SEM (scanning electron microscopy), AFM (atomic force microscopy), Raman spectroscopy, XAS (x-ray absorption spectroscopy), XES (x-ray emission spectroscopy), XPS (x-ray photoelectron spectroscopy) and XRD (x-ray diffraction).

Polytetrafluoroethylene (PTFE) is a highly scattering material and has been used as diffuse reflectors. In the present study, the ranges of the scattering coefficient, absorption coefficient, and the asymmetric parameter of the Henyey-Greenstein scattering phase function are assessed for semitransparent PTFE films whose thicknesses range from 0.11 mm to 10 mm. The bidirectional reflectance distribution function (BRDF) and bidirectional transmittance distribution function (BTDF) of these PTFE films were measured using a laser scatterometer at a wavelength of 635 nm, and the directional-hemispherical reflectance and transmittance were obtained by integrating BRDF and BTDF at normal incidence. The scattering coefficient of PTFE is estimated to exceed 1200 (1/cm). On the other hand, the absorption coefficient should be less than 0.01 (1/cm). A Monte Carlo simulation was employed to predict the BRDF and BTDF of PTFE films, and the calculations were compared with measurements at various incidence angles.

El síndrome de Budd-Chiari (SBC) es una enfermedad poco frecuente que no obstante afecta a población joven con una alta morbimortalidad. A pesar del gran esfuerzo investigador realizado, quedan aún por hacer avances en el conocimiento fisiopatológico y en el ámbito terapéutico, ambos estrechamente vinculados, que mejoren el pronóstico de estos enfermos. Sin embargo, la baja incidencia de esta enfermedad ha dificultado la realización de estudios prospectivos y la obtención de resultados de inequívoca interpretación.Mediante esta tesis, se estudian dos aspectos de esta entidad: uno fisiopatológico, cuyo objetivo es profundizar en el conocimiento de las consecuencias hemodinámicas sistémicas derivadas de la obstrucción al flujo venoso hepático; y otro terapéutico, que consiste en evaluar la utilidad de las prótesis recubiertas de politetrafluoroetilino (PTFE) en el TIPS comparándolas con prótesis no recubiertas con el objetivo de contrastar su eficacia. Para llevar a cabo el primer estudio de esta tesis doctoral, se evaluan parámetros hemodinámicos sistémicos, sistemas neurohumorales vasoactivos y expansión de la volemia plasmática en enfermos con SBC, y en segundo lugar se comparan los resultados hemodinámicos de enfermos con SBC frente a una cohorte de enfermos cirróticos con hipertensión portal sinusoidal. El hallazgo más notable es que los enfermos con SBC grave presentan activación de los sistemas neurohumorales vasoactivos con actividad de renina plasmática elevada y niveles elevados de aldosterona y norepinefrina. Esta activación también se acompañó de un aumento de la volemia plasmática. Sin embargo, y a diferencia de lo que ocurre en enfermos con hipertension portal sinusoidal y presinusoidal, los enfermos con SBC no presentan descenso de las resistencias vasculares sistémicas totales, al menos en fases iniciales, lo cual sugiere que otros mecanismos fisiopatológicos son responsables de la activación de sistemas vasoactivos y de la expansión de la volemia. En la cohorte de enfermos estudiada el gasto cardiaco permanece en rangos normales. Es probable que la ausencia de anemia y la disminución del retorno venoso influyan evitando un aumento del gasto cardiaco a pesar del aumento en la volemia plasmática.En el segundo estudio se parte de la hipótesis de que el empleo de las nuevas prótesis recubiertas de PTFE, utilizadas para el TIPS de enfermos con SBC, se asocia a una menor tasa de disfunciones y disminuyen las complicaciones asociadas, mejorando los resultados obtenidos con prótesis no recubiertas. Para ello se compara los efectos de las distintas prótesis sobre la tasa de disfunción del TIPS y eventos clínicos. En segundo lugar, se compara el número de reintervenciones (angioplastias, restenting) necesarias para mantener el shunt permeable y número total de prótesis utilizadas; número de ingresos y días de hospitalización durante el seguimiento en ambos grupos. Por ultimo, se evalúa la seguridad y eficiencia del empleo de prótesis recubiertas en enfermos con SBC que requieren un TIPS. Se demuestra que en los pacientes con SBC grave el TIPS constituye un tratamiento seguro y eficaz que controla los síntomas de la enfermedad refractaria a tratamiento médico. Las nuevas prótesis recubiertas de PTFE en el TIPS mejoran la tasa de disfunción por estenosis o trombosis con respecto a las prótesis no recubiertas. A su vez, la menor tasa de disfunción observada repercute en un menor número de reintervenciones, ingresos hospitalarios y días de estancia hospitalaria. En base a los resultados de este segundo estudio las prótesis recubiertas de PTFE deberían ser la primera opción al utilizar el TIPS en enfermos con SBC. / Budd-Chiari syndrome (BCS) is an uncommon liver disease defined as an obstruction to hepatic venous outflow. The obstruction of the hepatic venous outflow leads to sinusoidal congestion, centrilobular necrosis, fibrosis and portal hypertension with severe complications. In order to deepen in the BCS, the first study address the hemodynamic changes that take place in BCS, which are well described in cirrhotic patients with sinusoidal portal hypertension, but remain uncertain in Budd-Chiari patients with postsinusoidal portal hypertension. In a large series of patients with advanced BCS, the systemic circulation, the vasoactive neurohumoral systems and plasma volume were assessed and compared with the systemic hemodynamics of those obtained in a group of cirrhotic patients. BCS patients had mean systemic, cardiopulmonary pressures and cardiac index within normal range, but significantly different from that of a group of cirrhotic patients. Despite most of the BCS patient exhibited normal systemic vascular resistance, BCS patients had activation of the neurohumoral vasoactive systems and plasma volume expansion. In conclusion, patients with BCS had activation of vasoactive neurohumoral systems and expanded plasma volume. This was observed despite these patients did not show increased CI and systemic vasodilation, which is in marked contrast with what is observed in patients with cirrhosis of the liver.The second study focus on the treatment of BCS patients with portal hypertension, with transjugular intrahepatic portosystemic shunts (TIPS) using new developed stents. The polytetrafluoroethylene (PTFE)-covered stents have demonstrated to decrease shunt dysfunction in cirrhosis. Therefore, the aim of this study was to analyze and compare the incidence of TIPS dysfunction in patients treated with bare stents and covered stents. After a median follow-up period of nearly 2 years, 87% of patients receiving bare stents had TIPS dysfunction vs. 33% receiving PTFE-covered stents (actuarial rates of primary patency 19 % vs. 67 % at 1 year). Futhermore, the number of additional interventional procedures to maintain TIPS patency and clinical relapses were significantly greater in the bare stent than in the PTFE-covered stent group. In conclusion, our findings suggest that PTFE-covered stents should be preferred in these patients.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-08-10T11:35:31Z No. of bitstreams: 1 RobertoKleciusMendoncaFernandes_TESE.pdf: 9615422 bytes, checksum: cd708447bea2bf643fce86924f5bbab0 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-08-11T10:55:04Z (GMT) No. of bitstreams: 1 RobertoKleciusMendoncaFernandes_TESE.pdf: 9615422 bytes, checksum: cd708447bea2bf643fce86924f5bbab0 (MD5) / Made available in DSpace on 2017-08-11T10:55:04Z (GMT). No. of bitstreams: 1 RobertoKleciusMendoncaFernandes_TESE.pdf: 9615422 bytes, checksum: cd708447bea2bf643fce86924f5bbab0 (MD5) Previous issue date: 2017-05-15 / O mancal seco ? um elemento estrutural presente na maioria dos sistemas mec?nicos das ind?strias dos setores eletrodom?sticos, agropecu?rios, aeroespacial, aeron?utico e automotivo. Este trabalho d? continuidade a uma linha de pesquisa iniciada no Grupo de Estudos de Tribologia e Integridade Estrutural (GET) da Universidade Federal do Rio Grande do Norte (UFRN) e tem o objetivo de investigar tribologicamente comp?sitos polim?ricos com matriz de politetrafluoretileno (PTFE) e carga de rejeito de scheelita para aplica??o em mancais secos, visando reduzir custo e aumentar a vida em servi?o destes elementos. O rejeito de scheelita, origin?rio da extra??o da scheelita utilizada para produ??o do tungst?nio, ? um res?duo mineral composto de ?xidos, como os de sil?cio, c?lcio, alum?nio, ferro, magn?sio, tungst?nio, dentre outros. O rejeito de scheelita foi caracterizado na condi??o como adquirido, atrav?s de an?lises de MEV e EDS, e peneirado para tamanho de part?cula inferior a 45 ?m. O PTFE foi analisado por DRX. PTFE e rejeito de scheelita foram misturados mecanicamente, moldados por compress?o a quente, num molde projetado envolto por uma resist?ncia el?trica, atrav?s de uma prensa hidr?ulica. Investigou-se o desempenho tribol?gico dos comp?sitos submetidos a cargas (1) em movimento linear alternado (reciprocating) e (2) com indenta??es repetidas. As superf?cies novas e ensaiadas foram analisadas por Microscopia de For?a At?mica (AFM) no que concerne aos par?metros de rugosidade peri?dica e n?o peri?dica. Verificou-se que a varia??o no teor de rejeito de scheelita e a frequ?ncia do movimento alternado influenciaram no desempenho tribol?gico e na resist?ncia do comp?sito, relacionados ao coeficiente de atrito, ? rugosidade, ao desgaste e ? indenta??o. Os comp?sitos polim?ricos desenvolvidos e ensaiados demonstraram se constituir em novos materiais adequados para aplica??o de mancais secos, notadamente o comp?sito com 80% de PTFE e 20% de rejeito de scheelita que, mostrando-se como de melhor desempenho tribol?gico, apresenta-se como uma alternativa vi?vel e de custo mais baixo que o PTFE puro. / Dry rubbing journal bearing is a structural part that is present in the most of mechanical systems of industries from home appliances, agricultural, aerospace, aeronautic and automotive sectors. This work gives continuity to a research started in Group of Studies in Tribology and Structural Integrity (GET) at Federal University of Rio Grande do Norte (UFRN) and has objective to investigate, tribologically, a scheelite tailings- filled PTFE composites to dry rubbing journal bearings application, to reduce cost and extend life service of this parts. The tailing of scheelite, obtained from scheelite mining to produce tungsten, is a mineral spoilage composed of oxides, as a silicon oxides, calcium, aluminum, iron, magnesium, tungsten and others. The tailing of scheelite was analyzed as acquired through SEM and EDS analysis, and sieved to get a particle size less than 45 ?m. PTFE was analyzed through XRD. PTFE and scheelite tailings was mechanically mixed, hot compression molding in a designed mold involved by a electrical resistance and compressed by a hydraulic press. It was investigated tribological performance of composites subject to loads (1) in reciprocating movement and (2) repeated indentations. The new and tested surfaces were analyzed through Atomic Force Microscope (AFM) to collect periodic and non periodic roughness parameters. It was verified that scheelite tailing content and frequency of reciprocating influenced tribological performance and strength of composites, related to coefficient of friction, roughness, wear and indentation. The developed and tested polymeric composites showed to constitute a new materials suitable to dry rubbing journal bearings applications, notably 80% of PTFE and 20% scheelite tailing composite content that was the best tribological performance composite and being introduced as a viable alternative and lower cost than pure PTFE.

Presented work is focused on the deposition and characterization of thin and ultrathin plasma polymer films, then also on the preparation of nanocomposites metal/plasma polymer. The characterization of plasma polymer films was partly done in-situ without exposing the samples to the atmosphere. The thickness of prepared films was measured by spectral ellipsometry, the chemical composition was measured by XPS. The morphology and optical properties of deposited films were measured ex-situ. It is shown that during the initial stages of growth the properties of plasma polymer films depend on their thickness and also on the material of the substrate. Many interesting applications were explored for prepared nanocomposites metal/plasma polymer. They can be used as superhydrophobic coatings, gradient coatings, substrates for Raman spectroscopy or as antibacterial coatings. Moreover, special optical properties of prepared nanocomposites were studied in detail. Presented work has an experimental character.

Duroplastische Materialien zeichnen sich durch eine sehr gute chemische und thermische Beständigkeit aus. Belastbare Informationen über das tribologische Materialverhalten von Duroplasten bei erhöhten Temperaturen und erhöhter mechanischer Beanspruchung sind nur teilweise vorhanden und sollen im Rahmen der Untersuchungen ermittelt und verifiziert werden. Das Ziel ist die Untersuchung der Prozess-Struktur-Eigenschaftsbeziehung bezüglich der Einbringung von PTFE in einem phenolharzbasierten Duroplast zur Verbesserung der tribologischen Materialeigenschaften und die Detektion der in der Grenzfläche wirkenden Effekte. Weiterführend soll eine fundierte wissenschaftliche Basis zur Übertragung der gewonnenen Erkenntnisse auf mögliche großserientaugliche Anwendungen geschaffen werden.

This project investigated the manufacturing of large diameter welded PTFE rings.This welding process is time consuming and can take over ten hours for one complete weld cycle. Additionally, the welds can have poor quality in the center of the material due to insufficient heating across the weld face. The goal of this research was to address these two issues by analyzing the current process to determine the root cause of weld failures while also determining the feasibility of reducing the weld cycle time. The scope of this thesis was to develop a model to better understand and simulate the current process which could then be used for design future improvements.<div><br></div><div>A MATLAB model of the current process was developed to simulate the transient heating cycle of the most common weld cycle for PTFE currently used by a manufacturer of PTFE seals. The data for the material properties was gathered from the manufacturer test data as well as from Lau et al. (1984). Temperature dependent material properties were used in the program because the PTFE is heated above its melting point during the weld cycle. Because of the complexity of this heat transfer problem, the heat flux in the model was tuned so that it accurately reflected the current process. This is because the goal of this study was not to determine the exact heat fluxas it was unknown, but to develop an accurate model. Thus, the heat flux was assumed and the model was then verified with process data. Results from the model were compared to validation results from a FLIR thermal camera. The model predicted the compared temperatures to within 3.1% error at both 15-minute and 90-minute intervals. Though there are many potential sources of error in the process and the thermal camera measurement, the model was deemed acceptable as a model of the current process. A semi-infinite heat analysis was calculated to simulate a hot plate welding method on the PTFE. This showed that the temperature of the weld face could be raised by 57.275°C. It is believed that a method similar to hot plate welding applied to PTFE could heat the material faster and more evenly than the current process, reducing the weld failures and cycle time.<br></div>