Several approaches have been used to develop carbon nanotube (CNT) based electrochemical supercapacitors. These approaches include the following: (a) stabilization and carbonization of ternary composites of polyacrylonitrile (PAN), poly (styrene co-acrylonitrile) (SAN) copolymer, and single wall carbon nanotubes (SWNTs); (b) SWNT membranes functionalized with aryl chloride, sodium sulfonate, aryl sulfonic acid, bis(3,5-di-tert-butylphenyl)5-aminobenzene-1,3-dioate, and 4,4 -methylenedianiline; and (c) pyrrole treated SWNTs. In addition nitric acid functionalized and heat-treated SWNT membranes have been studied. The electrochemical supercapacitor behavior of these membrane electrodes has been characterized by cyclic voltammetry, constant current charging-discharging, and impedance analysis in aqueous and ionic liquid electrolytes. Long term performance of selected electrodes has been evaluated. The surface area and pore size distribution was quantified by N2 gas adsorption/desorption and correlated with capacitance performance. The surface functional groups have been characterized by X-ray photoelectron spectroscopy. CNT electrode/electrolyte interaction has been characterized using contact angle measurements. Electrolyte absorption by the electrodes has also been characterized. Carbonized PAN/SAN/SWNT ternary composites exhibit double layer capacity of over 200 μF/cm2. By comparison, the double layer capacity of classical meso-porous carbons is in the range of 10-50 μF/cm2. The capacitance of functionalized SWNTs is up to 2 times that of the control bucky paper made from unfunctionalized SWNTs. Energy density of functionalized electrodes when evaluated in an ionic liquid is as high as 28 kJ/kg. High capacitance (up to 350 F/g) was obtained for pyrrole-treated functionalized SWNT membranes in 6 M KOH. This value is almost seven times that of the control bucky paper. Correlating the capacitance with surface area and pore size distribution, it was observed that macropores (pore width greater than 50 nm) play an important role for achieving high capacitance.

Made available in DSpace on 2016-12-08T17:19:14Z (GMT). No. of bitstreams: 1 iniciais.pdf: 130139 bytes, checksum: cfb58dd0103455dbb6c7b372a4cf5ad3 (MD5) Previous issue date: 2005-02-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Aiming the study of miscibility and mechanical properties, blends of poli(styrene-coacrylonitrile) (SAN) with poli(butadiene-co-acrylonitrile) (NBR) rubbers were prepared by casting, co-precipitation and extrusion followed by injection, varying acrylonitrile (AN) contents from 32,7 to 45% (w/w) in NBR. The blends were prepared in the compositions: SAN/NBR 90/10, 80/20, 70/30, 60/40 and 50/50 (w/w) and valued by Infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC), Scanning electron micrographs (SEM), Tensile and Izod impact tests. FTIR analyses of casting blends displayed that not happened reactions or specific interactions between polymers during blending because did not happened a shift in the spectrum blends bands. The DSC analyses of casting blends showed total imiscibility to SAN/NBR 50/50 blend (AN contents in NBR 32,7%), partial miscibility to the 60/40, 70/30 and 80/20 compositions and total miscibility to the 90/10 composition. The SAN/NBR blends (AN contents in NBR 39%), prepared by casting and coprecipitation revealed partial miscibility for all compositions. Coprecipitated blends prepared with AN rubber content of 45% showed partial miscibility to 50/50, 60/40, 70/30 and 90/10 compositions and total miscibility to 80/20 composition. The phase morphology was influenciated by blending methods, casting blends revealed dispersed spherical elastomeric domains in matrix while coprecipitated blends form co continuous phase. The NBR addition result in significant impact resistant increase but decrease in tensile strenght / Com o objetivo de estudar a miscibilidade e propriedades mecânicas, foram preparadas blendas do copolímero poli(estireno-co-acrilonitrila) (SAN) com o copolímero poli(butadienoco-acrilonitrila) (NBR). As blendas foram preparadas por três métodos diferentes: evaporação de solvente, co-precipitação e extrusão seguida de injeção, variando o teor de acrilonitrila no NBR de 33 a 45 % (m/m). As blendas foram preparadas nas composições SAN/NBR 90/10, 80/20, 70/30, 60/40 e 50/50 (m/m) e avaliadas por Espectroscopia na região do infravermelho com Transformada de Fourrier (FTIR), Calorimetria diferencial exploratória (DSC), Microscopia eletrônica de varredura (MEV), Ensaios de Tração e Impacto Izod. As análises de FTIR das blendas preparadas por evaporação de solvente mostraram não ter ocorrido nenhuma reação nem interação específica entre os polímeros durante o processo de mistura porque não houve deslocamentos, aparecimento ou desaparecimentos de picos no espectro das blendas em relação ao espectro dos polímeros puros. O DSC avaliou a miscibilidade das blendas preparadas por evaporação de solvente e co-precipitação. A blenda SAN/NBR 50/50, preparada por evaporação de solvente, (NBR contendo 32,7% de acrilonitrila), é totalmente imiscivel, as composições 60/40, 70/30 e 80/20 são parcialmente miscíveis e a composição 90/10 formou um sistema miscível. As blendas SAN/NBR (NBR contendo 39% de acrilonitrila), preparadas por evaporação de solvente e co-precipitação, mostraram-se parcialmente miscíveis em todas as composições. As blendas preparadas por co-precipitação usando a borracha com 45% de acrilonitrila são parcialmente miscíveis com exceção da composição 80/20 que é totalmente miscível. A morfologia de fase foi influenciada pelo método de preparação das blendas, aquelas preparadas por evaporação de solvente mostraram domínios elastoméricos ovais dispersos na matriz SAN, enquanto que as preparadas por coprecipitação apresentaram fases semi-contínuas. A resistência ao impacto foi significativamente aumentada pela incorporação do NBR no SAN porém com decréscimo do Módulo de Young.

Made available in DSpace on 2016-12-08T17:19:35Z (GMT). No. of bitstreams: 1 Tatiana da Cunha Gomes Leitzke.pdf: 2438825 bytes, checksum: 8c0dbce0f01fadf8eb99d5b68ba3e534 (MD5) Previous issue date: 2003-02-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Aiming the development of polymer materials with high toughness, poly(butadiene-coacrylonitrile) rubbers (NBRs), with acrylonitrile (AN) contents varying from 32,9 to 45,7%, were added to poly(styrene-co-acrylonitrile) (SAN) by casting, mini-extrusion and monoscrew extrusion followed by injection molding. Addition of NBR resulted in significant improvements in the impact strength and the elongation at break, that were strongly influenced by the blend composition, the AN contents and the NBR melt viscosities, but the tensile strength is slightly decreased. The best impact strength results (157,1 ± 3.7 J/m) were obtained with a 70/30 (w/w) SAN/NBR blend using NBR with 33,1% of AN and 51 ML 1+4 (100°C), being ca. 700% higher than the values for pure SAN (22,4 ± 1.1 J/m). Differential scanning calorimetry (DSC) measurements indicated a partial miscibility between the copolymers, showing a shifting of the SAN glass transition temperature from 108,1 to 101,7oC for the 70/30 blend with NBR containing 45,7% of AN. This is in agreement with infrared spectroscopy (FTIR) analysis that displayed a significant shift of the dienic band from 967 cm-1 to ca. 1060 cm-1 for all 70/30 blends, suggesting segmental interactions between NBR and SAN. Scanning electron micrographs (SEM) from fracture surfaces revealed homogeneously dispersed spherical elastomeric domains, and the appearance of yielding and/or crazing processes for all blends. The size of NBR domains decreased as the AN content increased, while the number of NBR domains decreased as the melt viscosity increased. From these results it can be concluded that SAN thoughening by the addition of NBR is directly related to the AN content and the melt viscosity of the elastomer, depending on the morphology of the dispersed rubber phase. Higher NBR domain sizes cause better impact strengths, as large rubber particles are more effective in initiating crazing processes. / Com o objetivo de desenvolver materiais poliméricos com elevada tenacidade, borrachas de poli(butadieno-co-acrilonitrila) (NBR), com teores de acrilonitrila variando de 32,9 a 45,7%, foram incorporadas ao poli(estireno-co-acrilonitrila) (SAN), por evaporação desolventes, mini-extrusão e extrusão seguida de injeção. A adição do NBR resultou em um aumento significativo na resistência ao impacto e na deformação na ruptura, que foram fortemente influenciadas pela composição da blenda, pelo teor de acrilonitrila e pela viscosidade dos NBRs, porém, houve a diminuição da resistência à tração. O melhor resultado de resistência ao impacto (157,1 ± 3.7 J/m) foi obtido para a blenda 70/30 (m/m) utilizando NBR com 33,1% de acrilonitrila e 51 ML 1+4 (100°C), um valor cerca de 700% maior que o verificado para o SAN puro (22,4 ± 1.1 J/m). A técnica de calorimetria diferencial de varredura (DSC) indicou uma miscibilidade parcial entre os copolímeros, mostrando o deslocamento da temperatura de transição vítrea do SAN de 108,1 a 101,7ºC para a blenda 70/30 utilizando o NBR com 45,7% de acrilonitrila. Este resultado concorda com a análise de espectroscopia de infravermelho (FTIR), que mostrou um deslocamento significativo da banda da parte butadiênica de 967 cm-1 para 1060 cm-1, para todas as blendas 70/30, sugerindo assim interações segmentais entre o NBR e SAN. A análise da superfície de fratura por microscopia eletrônica de varredura (MEV), revelou homogeneidade dos domínios elastoméricos dispersos na matriz, bem como o aparecimento de microtrincas e/ou deformação plástica para todas as blendas. O tamanho dos domínios de NBR diminui com o aumento do teor de acrilonitrila presente no NBR, enquanto a quantidade de domínios diminui com o aumento da viscosidade. A partir destes resultados conclui-se que a tenacificação do SAN com a adição de NBR está diretamente relacionada com o teor de acrilonitrila e viscosidade do elastômero e depende da morfologia da fase elastomérica dispersa na matriz. Os domínios maiores de NBR proporcionaram melhor resistência ao impacto, sendo que partículas de borracha maioresfavorecem o aparecimento de microtrincas.

In recent years, increased use of electronic devices and wireless operations resulted in unavoidable electromagnetic (EM) pollution which has a significant impact on civil and military sectors. Considering the foremost requirement, huge efforts were invested in the development of electromagnetic interference (EMI) shielding materials. In this context, metals are usually preferred but design complexities like high density and susceptibility towards corrosion are limiting factors; additionally, the reflection of microwaves from the surface fails to serve as EM absorbers. The concern here is to minimize the reflection of the high frequency electromagnetic wave from the surface and to enhance the microwave absorption in GHz frequencies. In this thesis, we have made an attempt to design EMI shielding materials with exceptional absorption ability derived from Polycarbonate (PC)/ Poly styrene-co-acrylonitrile (SAN) based polymer blends. Herein, unique co-continuous micro-phase separated blend structures with selective localization of microwave active nanoparticles in one of the phases were realized to be most effective for microwave attenuation over just dispersing it in one polymer matrix (i.e. PC and SAN composites). The synergistic attenuation of electric and magnetic field associated with EM radiation was achieved through incorporation of various magnetic nanoparticles, however, dispersion of magnetic nanoparticles was a challenging task. Therefore, in order to localize magnetic nanoparticles in PC phase of the blends and to enhance the dispersion state, various modification strategies have been designed. In summary, we have developed a library of engineered nanoparticles to achieve synergistic attenuation of EM radiation mostly through absorption. For instance, the PC/SAN blends containing MWNTs and rGO-Fe3O4 nanoparticles manifested in exceptional EMI shielding, well above required shielding effectiveness value for most of the commercial applications, essentially through absorption. Taken together, the finding suggests that immiscible blends containing MWNTs and the decoration of magnetic nanoparticles (rGO-Fe3O4) on the surface of reduced graphene oxide sheets can be utilized to engineer high-performance EMI shielding materials with exceptional absorption ability.