Development of new device for measuring the thermal conductivity of polymeric nanocomposite materials

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Measurement of thermal conductivity of polymeric nanocomposite materials

A measuring device of the thermal conductivity of Polymeric nanocomposite materials is presented. This project is a continuation of a previous master student work. The goal of this project is to build a miniaturized version of the previous device in order to overturn certain limitations and improve its overall performance. The new device uses much smaller size samples, which ensures sample integrity/rigidity and saves material which in the case of nanoadditives may be expensive or scarce. In addition, the device is affordable and portable without compromising the operation convenience and precision/accuracy. As in the previous work, the device is based on the hot/cold tank principle, which is simple and easy to operate, is non-destructive to the sample, is safe to use and thermal conductivity is estimated through a simple mathematical model. The technique relies on recording the temperature evolution of a fluid in two separate tanks exchanging heat to each other. One tank contains a hot fluid (45-55°C), and the other a cold fluid (room temperature), while heat is being transferred through a sample placed in between the tanks. The development of the device is thoroughly described in this work. It starts from the apparatus conceptual design, its construction (including auxiliary units, e.g. for agitation, temperature measurement, data logging), preliminary tests to show proof of concept, technical and functional validation, (accuracy and precision when testing known polymeric materials), and ends with measuring the thermal conductivity of newly synthesized polymeric nanocomposite materials. Teflon samples are used first for the validation of the device's capacity, with the acquired results of thermal conductivity being in good agreement with literature values and also with measurements of the previous version of the device. Next, samples of polymeric nanocomposites of different nano additives concentrations are measured. Results demonstrate that the thermal conductivity of two types of epoxy resins (EPON828,827) increases with the addition of different concentrations of nano additives such as; Alumina (Al2O3), Boron nitride (BN), Silicone Carbide (SiC), Organoclay nanomere (I.30E), carbon nanotubes (CNT's) and different Silicone dioxide (SiO2) additives. It is found that some additives such as Alumina yield observable impact on the thermal conductivity of the epoxy resin whereas others such as multi-walled carbon nanotubes (MWCNT's) give a noticeable effect only at the higher examined concentrations. In the absence of additives, no impact on the epoxy resin thermal conductivity is observed when cured by different curing agents such as D2000, D230 and IPD. On the contrary, in the presence of additives, a clear effect of the curing agents D2000, D230 on the thermal conductivity of epoxy resin is observed. The significance of the nanocomposites curing process and the impact of achieving good degree of dispersion of the nanoadditives in the polymeric matrix is discussed

Measurement of thermal conductivity of polymeric nanocomposite materials

A measuring device of the thermal conductivity of Polymeric nanocomposite materials is presented. This project is a continuation of a previous master student work. The goal of this project is to build a miniaturized version of the previous device in order to overturn certain limitations and improve its overall performance. The new device uses much smaller size samples, which ensures sample integrity/rigidity and saves material which in the case of nanoadditives may be expensive or scarce. In addition, the device is affordable and portable without compromising the operation convenience and precision/accuracy. As in the previous work, the device is based on the hot/cold tank principle, which is simple and easy to operate, is non-destructive to the sample, is safe to use and thermal conductivity is estimated through a simple mathematical model. The technique relies on recording the temperature evolution of a fluid in two separate tanks exchanging heat to each other. One tank contains a hot fluid (45-55°C), and the other a cold fluid (room temperature), while heat is being transferred through a sample placed in between the tanks. The development of the device is thoroughly described in this work. It starts from the apparatus conceptual design, its construction (including auxiliary units, e.g. for agitation, temperature measurement, data logging), preliminary tests to show proof of concept, technical and functional validation, (accuracy and precision when testing known polymeric materials), and ends with measuring the thermal conductivity of newly synthesized polymeric nanocomposite materials. Teflon samples are used first for the validation of the device's capacity, with the acquired results of thermal conductivity being in good agreement with literature values and also with measurements of the previous version of the device. Next, samples of polymeric nanocomposites of different nano additives concentrations are measured. Results demonstrate that the thermal conductivity of two types of epoxy resins (EPON828,827) increases with the addition of different concentrations of nano additives such as; Alumina (Al2O3), Boron nitride (BN), Silicone Carbide (SiC), Organoclay nanomere (I.30E), carbon nanotubes (CNT's) and different Silicone dioxide (SiO2) additives. It is found that some additives such as Alumina yield observable impact on the thermal conductivity of the epoxy resin whereas others such as multi-walled carbon nanotubes (MWCNT's) give a noticeable effect only at the higher examined concentrations. In the absence of additives, no impact on the epoxy resin thermal conductivity is observed when cured by different curing agents such as D2000, D230 and IPD. On the contrary, in the presence of additives, a clear effect of the curing agents D2000, D230 on the thermal conductivity of epoxy resin is observed. The significance of the nanocomposites curing process and the impact of achieving good degree of dispersion of the nanoadditives in the polymeric matrix is discussed

Game theory and relative gains: strategic constraints of international cooperation

Esta dissertação analisa, conceitual e metodologicamente, a questão dos ganhos relativos na teoria de Relações Internacionais. A análise passa pelo exame da literatura relevante, e pela apreciação da utilização que essa literatura faz do ferramental de teoria dos jogos. Identifica-se um problema metodológico ligado à escolha das premissas comportamentais dos jogadores. Na tentativa de contribuir para remediar essa lacuna, é elaborado um conceito, chamado de preço da cooperação, para explicar como varia a predileção por ganhos absolutos ou relativos por parte dos estados (jogadores). A análise sugere que a sensibilidade à distribuição de ganhos gerada pela preocupação dos estados com segurança é apenas uma das fontes dessa sensibilidade. De modo que os efeitos do problema dos ganhos relativos sobre a cooperação internacional devem ser pensados e investigados levando-se em conta um conjunto de fatores causadores de problemas de ganhos relativos, com destaque para os conflitos distributivos inerentes às barganhas.This dissertation analyses the problem of relative gains in International Relations theory, both from a conceptual and a methodological point of view. The research examines the relevant literature and investigates how it uses the tools provided by game theory. The research focus on the problem of choosing the assumptions pertaining to the behavior of players, and proposes the concept of \"price of cooperation\" to explain the variation in players\' sensibility to relative gains. This study suggests that the concern with security is only one of many sources of sensibility to relative gains. As such, the effects of the relative gains problem upon international cooperation should be investigated taking into account the various factors that may increase preference for relative gains, with special attention to bargainings inherent distributive conflicts

Development of new device for measuring the thermal conductivity of polymeric nanocomposite materials

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Materials with fungi-bioinspired surface for efficient binding and fungi-sensitive release of antifungal agents.

Materials with fungi-bioinspired surface have been designed to host ergosterol-binding polyene antibiotics and to release them via a competitive mechanism only when fungi are present in the medium. Silicone rubber (SR) surfaces were endowed with selective loading and fungi-triggered release of polyene antifungal agents by means of a two-step functionalization that involved the grafting of glycidyl methacrylate (GMA) via a gamma-ray preirradiation method (9-21.3% wt grafting) and the subsequent immobilization of ergosterol (3.9-116.8 mg/g) to the epoxy groups of polyGMA. The functionalized materials were characterized using FTIR and Raman spectroscopy, thermogravimetric analysis (TGA), and fluorescence, scanning electron microscopy (SEM), and atomic force microscopy (AFM) image analyses. Specific interactions between natamycin or nystatin and ergosterol endowed SR with ability to take up these polyene drugs, while immobilization of ergosterol did not modify the loading of antifungal drugs that did not interact in vivo with ergosterol (e.g., miconazole). In a buffer medium, polyene-loaded ergosterol-immobilized slabs efficiently retained the drug (<10% released at day 14), while in the presence of ergosterol-containing liposomes that mimic fungi membranes the release rate was 10-to-15-fold enhanced due to a competitive displacement of the drug from the ergosterol-immobilized slab to the ergosterol-containing liposomes. Release in the presence of cholesterol liposomes was slower due to a weaker interaction with polyene agents. The fungi-responsive release was demonstrated for both polyene drugs tested and for slabs prepared with a wide range of amounts of immobilized GMA and ergosterol, demonstrating the robustness of the approach. Nystatin-loaded functionalized slabs were challenged with Candida albicans and showed improved capability to inhibit biofilm formation compared to nystatin-soaked pristine SR, confirming the performance of the bioinspired materials