Rozprawy doktorskie na temat „(poly)vinyl Alcohol(PVA) Nanocomposite”

Facial implants are becoming more common in America and across the world. In the United States last year, over 260,000 augmentation and reconstruction surgeries were performed on facial cartilage areas, while over two million soft tissue fillers were administered. The current implants on the market, though, are deficient in three major areas: they are too rigid, susceptible to migration, and require a large incision. Alternatively, dermal fillers lack shape and biodegrade too quickly. Poly(vinyl) alcohol (PVA) cryogel is a promising hydrogel alternative due to its softness, durable nature and ease of cast molding. While biocompatible, it does not elicit a fibrous response with firm adhesion and could migrate. The goal of this study is to develop a biodurable implant material that has soft-tissue elasticity, pores for adhesion, and swelling for small incisions. In this research, multiple porosity inducing methods are applied to PVA cryogel. These include a casting PVA cryogel over a porogen then leaching it in a solvent, a gaseous exothermic reaction, creating composites with biodegradable components, as well as using molds to alter the surface texture. Once created, the samples then underwent a series of tests to determine their mechanical properties which include elasticity, tensile strength, elongation, tear strength, pore size, and porosity. Swelling ratio of nonporous PVA cryogel was also considered. Porous PVA cryogel made with a high PVA weight percentage (30%) showed equivalent mechanical properties to that of cartilage. Porous PVA cryogel manufactured with a lower weight percent (10% and 20%) were shown to have similar elastic properties to that of adipose tissue. The surface texture methods, gas method, casting and leaching method, and composites made with CaPO4 and chitosan were all shown to create pores large enough for ingrowth. Samples created with a porosity large enough to encourage ingrowth include the gas method, casting and leaching method, and the CaPO4 composites. The swelling ratio was shown to increase as the weight percentage of PVA in the samples decreased. These quantified characteristics can be used to select the appropriate porous PVA cryogel required for a range of applications including facial implants.

Chronic lower back pain is a clinical manifestation of vertebral disc degeneration. An emerging technique, nucleoplasty, aims to target early stages of disc degeneration. It is envisioned to inject a liquid-state polymer, poly(vinyl alcohol) hydrogels, into the nuclear cavity and allowed to cure in-situ. Two formulations of poly(vinyl alcohol) hydrogels were investigated for its suitability as an injectable polymer. Therefore, its swelling ability, stiffness, required extrusion pressures and temperature dependent curing rates were characterized. Comparable to native nucleus pulposus tissue, the hydrogels swell approximately 10–20 wt% and maintained 1–2.5 MPa stiffness over eight weeks in immersed in phosphate buffer saline. Extrusion pressures highly varied for different hydrogel temperatures and lapsed time. Curing rates for the first hydrogel formulation were slow whereas the second formulation reached within 72 hrs about 70 % of its final cured stiffness. The second hydrogel formulation is a more promising candidate for clinical use.
La lombalgie chronique est la manifestation clinique de la dégénération des disques intervertébraux. La nucleoplastie est une nouvelle technique destinée à traiter la dégénération du disque dans ses premières phases. Le principe consiste à injecter un polymère sous forme liquide, l'hydrogel poly(vinyl alcool), dans le nucléus pulposus, et de le laisser durcir in situ. Deux types d'hydrogels poly(vinyl alcool) ont été étudiés ici pour cette application. La capacité à s'étendre, la rigidité, la pression requise pour l'extrusion et la vitesse de durcissement en fonction de la température ont ainsi été caractérisés pour chacun des deux polymères. Les hydrogels ont des caractéristiques semblables au nucléus pulposus naturel : ils s'étendent de 10 à 20 % en poids et, immergés dans du tampon phosphate salin, maintiennent une rigidité de 1-2.5 MPa pendant 8 semaines. La pression d'extrusion varie significativement avec la température de l'hydrogel et le temps écoulé. La vitesse de durcissement du premier hydrogel était lente, alors que le second atteignait 70 % de sa rigidité finale en moins de 72 heurs. Cette seconde formulation semble plus prometteuse pour des applications cliniques.

Thesis (M.S.)--School of Mechanical Engineering, Georgia Institute of Technology, 2005. Directed by Marc Levenston.
Marc Levenston, Committee Co-Chair ; Yves Berthelot, Committee Co-Chair ; Robert Guldberg, Committee Member. Includes bibliographical references.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2009.
In papermaking, the addition of filler can be detrimental to the properties of the resulting paper hence the use of additives that enhance paper properties are of paramount importance. Syndiotacticity rich poly(vinyl alcohol) (PVA) microfibrils were prepared for use as filler retention aids. They were prepared via in situ fibrillation during the saponification of high molecular weight poly(vinyl pivalate). The resulting fibers had high thermal stability and crystalline melting temperature. They were not fully soluble in water even at 100 oC. In order to make them less water resistant the syndiotacticity of the PVA microfibrils was varied by copolymerizing vinyl pivalate with vinyl acetate and saponifying the resultant copolymer. It was observed that changes in syndiotacticity had a significant effect on the crystallinity, morphology and thermal properties of the resultant PVA. The surfaces of the fibers were modified by first crosslinking using glyoxal (a dialdehyde), and then attaching cationic and anionic groups by grafting and by carboxymethylation. Crosslinking prior to modification was beneficial in minimizing the solubility of the fibers in the aqueous media in which they were modified. Heterogeneous modification techniques were employed so that fiber properties could be preserved. Carboxymethylation was carried out using the two step Williamson’s ether synthesis. The first step involves the formation of a highly reactive alkoxide by the reaction of PVA with a strong base and the second its etherification using a functional alkyl halide. Poly(methacryloyloxy ethyl trimethyl ammonium chloride) and poly(acrylic acid) were grafted from the PVA microfibrils using the KPS/Na2S2O3 redox initiation system. Grafting was confirmed by FTIR and NMR spectroscopy. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were carried out on both modified and unmodified PVA microfibrils. The results showed that crosslinking resulted in an enhancement of the thermal properties of the microfibrils. A decline in the onset temperature for thermal degradation and crystalline melting temperature were observed, and were attributed to the modification of the PVA microfibrils.

The induced rupturing of Poly Vinyl Alcohol (PVA) microbubbles with high mechanical index (MI)ultrasound beam is used in multiple medical application such as drug delivery, image contrastenhancement and perfusion imaging.In this work, Triggered imaging technique with subtraction algorithm is used to enhance themicrobubble’s (MB) contrast over tissue (CTR). The technique is performed by rupturing MBwith one destruction wave sequence followed by 100 B-mode imaging pulse sequences. Theimages obtained are then subtracted by a base image that is selected after the destruction pulse[1].The result of this technique depends mainly on the effectiveness of destruction pulse inrupturing highest number of MB. This has been tested through tissue mimicking phantomwithout replenishing the MB. The evaluation of the methods is done through the CTR and CNRcalculation for each of the 100 frames.The contrast enhancement technique used has also been tested with similar setup but withcontinuous replenishment of MB. The evaluation is done by comparing CNR and CTR results forthe 100 frames obtained by B-mode imaging with the ones resulted from the subtractionalgorithm.The contrast values obtained from both experiments are used in driving the characterization ofPVA response to high MI.The result for the destruction pulse effectiveness shows that the pulse indeed managed toreduce number of MB, but not to the lowest. This is because of leaked gas from cracked shell,the shell acoustic enhancement effect, and large bubbles which managed to survive.The Triggered imaging has shown large improvement in CTR value with use of the subtractionalgorithm when compared to B-mode results. In addition, it has provided an experimental wayfor perfusion imaging and quantification by monitoring CTR value after the destructive pulse[2]. This sets the bases for experimental research relevant to tissue perfusion at ultrasound labof KTH.

Orientador: Marcelo Ganzarolli de Oliveira
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica
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Resumo: Stents são malhas metálicas expansíveis usadas em procedimentos de angioplastia, para a desobstrução das artérias coronárias. Atualmente há um grande interesse na obtenção de stents revestidos com matrizes poliméricas eluidoras de drogas que impeçam a reoclusão da artéria (reestenose). S-nitrosotióis doadores de óxido nítrico (NO) como a S-nitrosoglutationa (GSNO) possuem potencial para a inibição da reestenose. Neste trabalho, placas metálicas e stents foram revestidos com filmes de PVA contendo GSNO (107 µmol/g) através da imersão em soluções de PVA/GSNO com concentrações de PVA de 0,5 a 10,0% m/v. Filmes de PVA/GSNO foram submetidos a ciclos de congelamento/descongelamento (C/D), e analisados em relação ao seu grau de cristalinidade, dissolução, intumescimento, morfologia e propriedades de difusão e eluição da GSNO. Análises por DSC e difração de raios X, mostraram que o grau de cristalinidade do PVA aumenta com o número de ciclos de C/D, e com a secagem por sublimação do filme congelado. O aumento da cristalinidade se reflete em uma diminuição da velocidade de eluição da GSNO para a fase aquosa e da velocidade de dissolução e grau de intumecimento da matriz. Os coeficientes de difusão (D) da GSNO através de filmes de PVA foram medidos utilizando-se uma cela tipo Franz com monitoramento espectrofotométrico. Verificou-se que os valores de D são menores nos filmes secos por sublimação e submetidos a um ciclo de C/D. Este resultado foi atribuído ao aumento da densificação da fase amorfa, obtido na secagem por sublimação. Os filmes secos por esta técnica, apresentaram uma estrutura tridimensional esponjosa constituída por filamentos interligados, revelada por microscopia eletrônica de varredura (MEV). Estimou-se que stents revestidos com PVA/GSNO, a partir de soluções de PVA 0,5 % (m/v) esterilizados com óxido de etileno a 45-55°C podem liberar cerca de 30 µmoles/g de PVA para a parede arterial e levaram à obtenção de revestimentos sem filmes entre as hastes metálicas
Abstract: Stents are expansible wire mesh tubes used in angioplasty procedures in order to widening the luminal diameter of the coronary arteries. There is currently a great interest in the development of stents coated with drug-eluting polymeric matrices, which are able to prevent future closure of artery (restenosis). S-nitrosothiols which are nitric oxide (NO) donors, like S-nitrosoglutathione (GSNO) have potential to inhibit restenosis. In the present work, metallic plates and stents were coated with GSNO (107 µmol/g)- containing PVA films through their immersion in PVA/GSNO solutions with PVA concentration ranging from 0.5 to 10.0% wt/v. PVA/GSNO films were submitted to freezing/thawing cycles (F/T) and analyzed concerning their crystallinity dissolution, swelling, morphology and GSNO diffusion and elution properties. DSC and X Ray diffraction analysis have shown that the PVA crystallinity degree increases with the increase in the number of F/T cycles, and with the drying of the frozen film by sublimation. The increase in cristallinity was reflected in a decrease of the rate of GSNO elution to the aqueous phase, dissolution rate and swelling degree of the matrix. The diffusion coefficients of GSNO through PVA films were measured using a Franz-like cell with spectrophotometric monitoring. It was verified that D values are lower in the films dried by sublimation and submitted to one FT cycle. This result was attributed to the increase in the densification of the amorphous phase obtained in the drying by sublimation. The films dried by this technique, displayed a spongelike three-dimensional structure made by interconnecting filaments, revealed by scanning electron microscopy (SEM). Stents coated with PVA/GSNO, from solution of PVA 0.5 % (wt/v) have avoided the formation of films between the wires of the stent mesh. It was estimated that these stents are able to release ca. 30 µmols/g of PVA to the arterial wall after sterilization with ethylene oxide at 45-55 °C
Mestrado
Físico-Química
Mestre em Química

Emulsion polymerizations of vinyl acetate (VAc) were performed by fully or partially replacing poly(vinyl alcohol) (PVA) with renewable materials as protective colloids or by adding renewable materials, as additives or fillers, to the emulsions during or after polymerization. The purpose of the study was to increase the amount of renewable materials in the emulsion. A total of 19 emulsions were synthesized. Different recipes were used for the synthesis. The following renewable materials were studied; hydroxyethyl cellulose (HEC) with different molecular weights, starch and proteins. HEC and starch were used as protective colloids. Proteins were used as additives or fillers. Cross-linking agent A and Cross-linking agent B were used as cross-linking agents. A total of 26 formulations were pressed, either cold or hot. The synthesized emulsions were evaluated with respect to pH, solids content, viscosity, minimum film formation temperature (MFFT), glass transition temperature (Tg), particle size and molecular weight (Mw). The tensile shear strengths of the emulsions were evaluated according to EN 204 and WATT 91. It was possible to fully, or partially, replace PVA as protective colloid with renewable materials. It was also possible to use renewable materials as additives or fillers in the emulsions. The emulsions obtained properties that differed from the reference. Generally, emulsions with HEC as protective colloid showed lower viscosity and slightly higher MFFT, Tg and molecular weight than emulsions with PVA as protective colloid. Larger particle sizes than the reference were obtained for emulsions containing PVA combined with renewable materials. The emulsion with starch as protective colloid exhibited the largest particle size. 10 formulations passed the criteria for D2. The emulsions where PVA was fully or partially replaced with HEC or starch showed a water resistance similar to the reference (around D2). The addition of protein did not decrease the water and heat resistance compared to the reference. Addition of protein after polymerization increased the water resistance (D2) compared to addition during polymerization. Addition of cross-linking agents did not increase the water resistance further. Two formulations passed the criteria for D3. The emulsion in the first formulation had PVA as protective colloid and protein B was added during polymerization. The emulsion in the second formulation had HEC as protective colloid. To both of these emulsions, protein A was added after polymerization, as a filler, combined with Cross-linking agent B as cross-linking agent before hot pressing. The first formulation also showed a good heat resistance (passed the criteria for WATT 91).

Os polímeros sintéticos compõem cerca de 20% do lixo urbano no Brasil. Além da não biodegradabilidade, formam uma camada impermeabilizante que impede a passagem de líquidos e gases originados no apodrecimento dos detritos, retardando a estabilização da matéria orgânica. A exploração da madeira produz uma grande quantidade de rejeitos que não são inteiramente aproveitados para gerar energia ou outros produtos, e acarreta sérios problemas ambientais. A finalidade deste trabalho é a produção de compósitos biodegradáveis reunindo rejeitos de madeira e um polímero biodegradável - o poli (álcool vinílico) [PVA]. Para facilitar a degradação do PVA, este foi modificado por anidrido ftálico (AF). A modificação foi estudada através de tempo de gelatinização, calorimetria exploratória diferencial (DSC) e análise termomecânica dinãmica (DMTA). Resíduos da madeira Sugi (Criptomeria japonica) foram refinados até a obtenção de uma farinha com partículas menores que 63 µ m. Esta farinha foi adicionada ao meio de reação AF/PVA. As proporções de AF e PVA, bem como os parâmetros utilizados na prensagem foram determinados segundo um planejamento estatístico fatorial. Os compósitos foram moldados a quente (180 C e 50 MPa). Variando-se a proporção AF/PVA, compósitos com valores de módulo de elasticidade (MOE) de ˜10 GPa e módulo de ruptura (MOR) de ˜90 MPa na flexão foram obtidos. Os valores são inferiores aos apresentados pelo polímero puro, seco e sem plasticizante (acima de 152 MPa), porém superiores às placas de madeira reconstituída de MDF e OSB, disponíveis comercialmente, que apresentam valores de MOR em torno de 49 MPa. A degradação por microorganismos foi avaliada pelo ensaio de soterramento utilizando uma adaptação do método para avaliar a resistência de materiais lignocelulósicos aos fungos da podridão mole (Publicação IPT No. 1157 D5). Os fungos da podridão mole que ocorreram naturalmente nos compósitos foram isolados e identificados segundo a técnica do microcultivo. O gênero mais frequente foi o celulolítico Trichoderma spp. e o mais degradador foi o Chaetomium spp. As mudanças na estrutura e na morfologia dos compósitos foram estudadas através de espectroscopia de infravermelho (IR) e microscopia eletrônica de varredura (MEV). As perdas de massa e das propriedades mecânicas foram monitoradas em intervalos pré-estabelecidos. Compósitos com altas concentrações de AF apresentaram biodegradabilidades superiores à da madeira maciça de Pinus sp. e levemente inferiores à da madeira de Eucalyptus grandis, utilizadas como referências. A biodegradabilidade se deve à facilidade dos grupos ésteres, dos ftalatos de PVA e de celulose, de serem hidrolizados e de regenerar o ácido ftálico. Mesmo sob hidrólise enzimática, a estrutura PVA-AF-celulose, que forma ligações cruzadas entre microfibrilas de celulose, não se desintegra, conservando as propriedades mecânicas por muito tempo. Estas se mantêm superiores, ao término de 180 dias de exposição, às da madeira maciça de Sugi antes de entrar no processo de biodegradação. Uma correlação entre a estrutura, as propriedades físicas e mecânicas, e a taxa de biodegradação dos compósitos de rejeitos de madeira-PVA foi estabelecida.
Synthetic polymers constitute around 20% of urban solid waste in Brazil. Besides being non-biodegradable, they form an impermeable barrier that prevents the liberation of liquids and gas originated in the waste deterioration, retarding organic matter stabilization. The wood industry produces large amounts of waste wood which is not entirely utilized to produce energy or other products, and it brings several environmental problems. The aim of this study is the production of an environmentally friendly wood-based product composed of waste wood and poly (vinyl alcohol) [PVA]. PVA is the most widely produced water soluble and biodegradable synthetic polymer worldwide. However, PVA degradation in aqueous and soil environments has proved to be quite slow under unadapted conditions. To accelerate its degradation, the PVA has been modified by phthalic anhydride (AF). These modifications have been studied by means of gelation time, Differential Scanning Calorimetry (DSC) and (Dynamic Mechanical Thermal Analysis (DMTA). Sugi (Criptomeria japonica) flour (particles size ‹ 63 µm) has been obtained by milling waste samples. Wood flour has been added into AF/PVA reaction medium. AF and PVA ratios and pressing conditions have been set by factorial design. The final pressing temperature and pressure have been set as 180 °C and 50MPa respectively. Varying AF/PVA ratios, composites presenting modulus of elasticity (MOE) values of ˜10GPa and modulus of rupture (MOR) of ˜90 MPa have been obtained. The MOR values are lower than that presented by the pure, dry, no plasticized PVA (higher than 152 MPa), but they are higher than commercial MDF (medium density fiberboard) and OSB (oriented strand board) of around 49 MPa. Degradation by microorganisms has been performed by soil burial test (method adapted from IPT Edition No. 1157 D5). Naturally occurring soft rot fungi have been isolated and identified according to micro cultivation techniques. Most frequent genus has been the cellulolytic Trichoderma spp. and most degrader has been Chaetomium spp. Changes in the composites microstructures and morphology throughout the biodegradation process have been studied by IR and SEM and decreasing in the mechanical properties monitored. The weight Ioss shown by composites with high AF concentration has been higher than the softwood Pinus sp. and comparable to the hardwood Eucalyptus grandis, utilized as witnesses. Even under enzymatic hydrolysis, the PVA-AF-cellulose structure has been only slightly broken, preserving considerable mechanical properties that remain superior to solid Sugi before entering any biodegradation process, even after 180 days of exposure. A correlation has been established between the structure, physical and mechanical properties and biodegradation rate of waste wood-PVA composites

Orientador: Marcelo Ganzarolli de Oliveira
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química
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Resumo: O Poli(álcool vinílico) (PVA) é polímero biocompatível que pode ser usado como matriz para a incorporação de S-nitrosoglutationa (GSNO), que é uma molécula endógena que exerce todas as funções bioquímicas do óxido nítrico (NO). Os principais objetivos deste trabalho foram a obtenção de filmes sólidos de PVA capazes de eluir GSNO localmente, que pudessem ser utilizados para aplicações tópicas e para o recobrimento de stents. Os filmes de PVA foram reticulados fisicamente através de ciclos de congelamento/descongelamento (C/D). Verificou-se que a aplicação de 1 a 5 ciclos C/D leva a um aumento da cristalinidade dos filmes comparada aos filmes não submetidos a C/D. Este efeito está associado ao aumento do raio de giro de estruturas espalhadoras de raios X e com a redução do coeficiente de difusão da GSNO. A liberação tópica de GSNO a partir de filmes de PVA na pele de voluntários levou a um aumento significativo do fluxo sanguíneo dérmico, medido por fluxometria com laser Doppler. Demonstrou-se que a aplicação de ciclos C/D pode ser usada para controlar a velocidade e a intensidade de aumento de fluxo sanguíneo. Filmes de PVA/GSNO aplicados como revestimentos de poços de placas de cultura de células mostraram atividade bactericida dose e tempo-dependentes contra cepas de S. aureus e P. aeruginosa, sendo capazes de esterilizar completamente estas duas bactérias multi-resistentes após 6 h de incubação. Filmes de PVA/GSNO permitiram a obtenção de revestimentos aderentes sobre a superfície de stents intracoronários de aço inox levando a uma redução significativa da adesão plaquetária após incubação com sangue total. Estes resultados permitem propor o uso de filmes de PVA/GSNO fisicamente reticulados para aplicações tópicas no tratamento de lesões infectadas, para promover a vasodilatação de tecidos isquêmicos e para a melhoria das propriedades hemocompatíveis de dispositivos de contato sanguíneo
Abstract: Poly(vinyl alcohol) (PVA) is a biocompatible polymer that can be used as a matrix for incorporation of S-nitrosoglutathione (GSNO), an endogenous molecule that exerts all the biochemical functions of nitric oxide (NO). The main objectives of this work were to obtain solid PVA films capable of releasing GSNO locally, which could be used in topical applications and for the coating for stents. PVA films were physically crosslinked through freezing-thawing cycles (F/T).It was observed that films subjected to 1 to 5 cycles shows higher crystallinity than films not subjected to F/T. This effect is associated with an increase in the gyration radius of the X-ray scattering structures an with a decrease in the GSNO diffusion coefficient. Topical GSNO release from PVA films on the skin of volunteers led to a significant increase of dermal blood flow, measured by laser Doppler flowmetry. It was shown that F/T cycles can be used to control the rate and intensity of blood flow increase. PVA/GSNO films applied as coatings of cell-culture plate wells showed dose and time-dependent bactericidal activities against S. aureus and P. aeruginosa, being able of completely sterilizing these mult-resistant bacteria after 6 h of incubation. PVA/GSNO films allowed the formation of adherent coatings on the surface of intracoronary stainless steel stents, and lead to a significant reduction of platelet adhesion after incubation with whole blood. These results allow suggesting the use of physically crosslinked PVA/GSNO films in topical applications for the treatment of infected lesions, for promoting the vasodilation of ischemic tissues and for improving the hemocompatible properties of blood contact devices
Doutorado
Físico-Química
Doutor em Ciências

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2005.
192 leaves on CD format, preliminary i-xii pages and numbered pages 1-135. Includes bibliography, list of figures and tables.
ENGLISH ABSTRACT: As a fibre reinforced material, engineered cementitious composite (ECC) has tough, strain-hardening behaviour in tension despite containing low volumes of fibres. This property can be brought about by developments in fibre, matrix and interfacial properties. Poly Vinyl Alcohol (PVA) fibre has been developed in recent years for ECC, due to its high tensile strength and elasticity modulus. However, the strong interfacial bond between fibre surface and matrix is a challenge for its application. This study focuses on the tailoring of matrix and fibre/matrix interfacial properties by cement replacement with fly ash (FA) and Ground Granulated Corex Slagment (GGCS). In this study the direct tensile test, three point bending test, micro-scale analysis, such as X-Ray Fluorescence Spectrometry analysis (XRF), Scanning Electron Microscope (SEM), are employed to investigate the influence of cement replacement, aging, Water/Binder (W/B) ratio, workability on ECC behaviour. This study has successfully achieved the aim that cement replacement by FA and GGCS helps to improve the fibre/matrix interfacial properties and therefore enhances the ECC tensile behaviour. Specifically, a high volume FA-ECC has stable high tensile strain capacity at the age of 21 days. This enables a constant matrix design for the investigation of other matrix influences. The Slag-ECC has a higher tensile strength but lower tensile strain capacity. The combination of FA and GGCS, moderate tensile strength and strain capacity is achieved Both tensile tests and Micro-scale analyses infer that the high volume FA-ECC has an adhesive type fibre/matrix interfacial interaction, as opposed to the cohesive type of normal PVA fibre-ECC. The different tensile behaviour trend of steel fibre-ECC and PVA fibre-ECC with the FA content is presented and discussed in this research. The investigations of aging influence indicate that the high volume FA-ECC has a beneficial effect on the properties of the composite at an early stage. However, at a high age, it has some difficulty to undergo multiple cracking and then leads to the reduction of tensile strain capacity. The modified mix design is made with the combination of FA and GGCS, which successfully increases the interfacial bond and, thereby, improves the shear transfer to reach the matrix crack strength. Therefore, an improved high age tensile behaviour is achieved. The W/B and fresh state workability influence investigations show that the W/B can hardly affect the tensile strain at early age. However, the workability influences on composite tensile strain significantly, because of the influence on fibre dispersion. Other investigations with regard to the hybrid fibre influences, the comparison of bending behaviours between extruded plate and cast plate, the relation between bending MOR and tensile stress, and the relation between compression strength and tensile strength contribute to understand ECC behaviour.
AFRIKAANSE OPSOMMING: As ‘n veselversterkte materiaal, het ontwerpte sementbasis saamgestelde materiale, taai vervormingsverhardingseienskappe in trek, ten spyte van lae veselinhoud. Hierdie eienskap word bewerkstellig, deur ontwikkelings in vesel, matriks en tussenveselbindingseienskappe. Poli-Viniel Alkohol (PVA) vesels is ontwikkel vir ECC, as gevolg van die hoë trekkrag en hoë modulus van hierdie veseltipe. Die sterk binding tussen die PVA-veseloppervlak en die matriks is egter ‘n uitdaging vir sy toepassing. Hierdie studie fokus op die skep van gunstige matriks en vesel/matriks tussenvesel-bindingseienskappe deur sement te vervang met vlieg-as (FA) en slagment (GGCS).In hierdie navorsing is direkte trek-toetse, drie-punt-buigtoetse, mikro-skaal analise (soos die X-straal ‘Fluorescence Spectrometry’ analise (XRF) en Skanderende Elektron Mikroskoop (SEM))toegepas. Hierdie metodes is gebruik om die invloed van sementvervanging,veroudering, water/binder (W/B)-verhouding en werkbaarheid op die meganiese gedrag van ECC te ondersoek.Die resultate van hierdie navorsing toon dat sementvervanging deur FA en GGCS help om die vesel/matriks tussenveselbindingseienskappe te verbeter. Dus is die ECC-trekgedrag ook verbeter. Veral ‘n hoë volume FA-ECC het stabiele hoë trekvervormingskapasiteit op ‘n ouderdom van 21 dae. Dit bewerkstellig ‘n konstante matriksontwerp vir die navorsing van ander matriks invloede. Die Slag-ECC het ‘n hoër treksterkte, maar laer trekvervormingskapasiteit. Deur die kombinasie van FA en GGCS word hoë treksterkte, sowel as gematigde vervormbaarheid in trek verkry. Beide trektoetse en mikro-skaal analise dui aan dat die hoë volume FA-ECC ‘n adhesie-tipe vesel/matriks tussenvesel-bindingsinteraksie het, teenoor die ‘kohesie-tipe van normale PVA vesel-ECC. Die verskille in trekgedrag van staalvesel-ECC en PVA vesel-ECC ten opsigte van die FA-inhoud is ondersoek en word bespreek in die navorsing. Die navorsing toon verder dat die hoë volume FA-ECC goeie meganiese eienskappe het op ‘n vroeë ouderdom. Op hoër ouderdom word minder krake gevorm, wat ‘n verlaging in die trekvervormingskapasiteit tot gevolg het. Met die kombinasie van FA en GGCS, word die vesel-matriksverband verhoog, waardeur ‘n verbetering in die skuifoordrag tussen vesel en matriks plaasvind. Verbeterde hoë omeganiese gedrag word daardeur tot stand gebring. Navorsing ten opsigte van die invoed van die W/B en werkbaarheid dui daarop dat die W/B slegs geringe invloed het op die trekvormbaarheid, terwyl die werkbaarheid ‘n dominerende rol speel in hierdie verband.Verdere studies sluit in die invloed van verskillende vesels, die vergelyking van die buigingsgedrag van geëkstueerde plate en gegote plate, die verhouding tussen buigsterkte en treksterkte, en die verhouding tussen druksterkte en treksterkte dra by tot beter begrip van die gedrag van ECC.

El presente trabajo tiene por objetivo estudiar las aplicaciones de los nanocristales o ¿nanowhiskers¿ extraídos mediante hidrólisis ácida de celulosa bacteriana (BCNW) para el desarrollo de materiales poliméricos y biopoliméricos con propiedades mejoradas para su uso en aplicaciones de envasado de alimentos. En primer lugar se estudió y optimizó el proceso de extracción de BCNW. Se desarrolló un procedimiento de extracción con ácido sulfúrico, que permitió obtener nanocristales con elevada relación de aspecto y cristalinidad y al mismo tiempo, un elevado rendimiento de extracción. Este procedimiento comprende una posterior etapa de neutralización que resultó ser necesaria para garantizar la estabilidad térmica de los nanocristales. El siguiente paso consistió en la formulación de materiales nanocompuestos con propiedades mejoradas incorporando BCNW en diferentes matrices plásticas, en concreto copolímeros de etileno-alcohol vinílico (EVOH), ácido poliláctico (PLA) y polihidroxialcanoatos (PHAs). Mediante las técnicas de electroestirado y estirado por soplado se generaron fibras híbridas de EVOH y PLA con BCNW. La incorporación de BCNW en las disoluciones empleadas para producir fibras modificó significativamente sus propiedades (viscosidad, tensión superficial y conductividad) y por tanto, la morfología de las fibras se vio afectada. Además, se generaron fibras con propiedades antimicrobianas mediante la incorporación de aditivos, maximizando el efecto antimicrobiano con la adición de sustancias de carácter hidrofílico. Seguidamente, se produjeron nanocompuestos por mezclado en fundido y se desarrollaron técnicas de pre-incorporación de BCNW para evitar la aglomeración de los mismos no sólo en matrices hidrofílicas como el EVOH, sino también en matrices hidrofóbicas como el PLA. La dispersión óptima de BCNW resultó en una mejora de las propiedades mecánicas y de barrera de los nanocompuestos. También se estudió la modificación de la superficie de los nanocristales mediante copolimerización con poli(glicidil metacrilato) para mejorar la compatibilidad de BCNW con una matriz hidrofóbica como el PLA. Se incluyen además los primeros resultados obtenidos en cuanto a la producción de nanobiocompuestos sintetizados por microorganismos, que consisten en PHAs con diferentes contenidos de hidroxivalerato reforzados con BCNW. Por último, se desarrollaron películas con propiedades de alta barrera basadas en películas de BCNW recubiertas con capas hidrofóbicas. El recubrimiento mediante la deposición de fibras por electrospinning seguido de homogeneización por calentamiento garantizó una buena adhesión entre las diferentes capas, protegiendo así las películas de BCNW del efecto negativo de la humedad.
Martínez Sanz, M. (2013). Bacterial cellulose nanowhiskers to enhance the properties of plastics and bioplastics of interest in food packaging [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/30312
TESIS
Premiado

It was found that a significant improvement of mechanical properties of CFRPs can be achieved by the adjustment of the matrix properties such as toughness and CF/matrix adhesion via the chemical modification, as well as the physical modification by a small amount of cheap and environment-friendly nano fibers. Based on investigation of fracture mechanisms at macro/micro scale, the effects of matrix properties and nano fiber on the mechanical properties of CFRP have been discussed. Subsequently, the relationship has been characterized by a numerical model to show how to modulate the parameters of the matrix properties to achieve excellent fatigue properties of CFRP.
博士(工学)
Doctor of Philosophy in Engineering
同志社大学
Doshisha University

Yes
Poly(vinyl alcohol) (PVA)/graphene oxide (GO) nanocomposite hydrogel as artificial cartilage replacement was prepared via freezing/thawing method by introducing polyethylene glycol (PEG). Efficient grafting of PVA molecules onto GO surface was realized by formation of hydrogen bonding, resulting in exfoliation and uniform distribution of GO in PVA matrix. By introduction of appropriate content of GO, the increased crystalline regions of PVA and the formation of GO centered second network structure led to the increase of the storage modulus and effective cross-linking density. And therefore the mechanical strength and toughness of the composite hydrogel were improved simultaneously: the tensile strength, elongation at break, and compressive modulus showed approximately 200%, 40%, and 100% increase of the neat PVA hydrogel. Besides, for the sample with 1.5 wt % GO content, the maximum force retention and dynamic stiffness were improved remarkably in the process of sinusoidal cyclic compression, and the compressive relaxation stress also increased significantly, indicating the enhancement of the compressive recoverable and antifatigue ability, and resistance to compressive relaxation by formation of high load-bearing, dense, and reinforcing double network structure. Moreover, more than 50% decrease in coefficient of friction was obtained for the composite hydrogel, and the worn surface presented relative smooth and flat features with sharp decreasing furrow depth, confirming the lubrication effect of GO-PEG. This study shows promising potentials in developing new materials for cartilage replacement with simultaneous combination of high mechanical property and excellent lubrication.

碩士
中原大學
化學研究所
90
This thesis can be divided into two parts. For the first part , a series of poly(vinyl alcohol)—clay nanocomposites （PCN）were prepared by dispersing the nanolayers of inorganic montmorillonite （MMT）clay into organic poly(vinyl alcohol) matrix via the in-situ thermal polymerization. The as-synthesized poly(vinyl alcohol) / montmorillonite （MMT）clay nanocomposites were subsequently characterized by FTIR, XRD and TEM. Thermal properties and chemical structures of this series of nanocomposites were studied and discussed with different feeding ratio of the montmorillonite in PVA matrix. This nanocomposites was found to display an enhanced heat resistance at increasing amount of clay loading. The optical transparency of PCN membranes was also found to decrease as the clay loading increased. For the second part, a series of poly(vinylcarbazole)（PVK）—clay nanocomposites （PCN）were prepared by dispersing the nanolayers of inorganic montmorillonite （MMT） / clay into organic poly (vinylcarbazole) matrix via the in photo polymerization. The as-synthesized poly (vinylcarbazole) / montmorillonite （MMT）clay nanocomposites were subsequently characterized by FTIR, XRD and TEM. Thermal properties and chemical structures of this series of nanocomposites were studied and discussed with different feeding ratio of the montmorillonite in PVK matrix. This nanocomposites was found to display an enhanced heat resistance at decreasing amount of clay loading. The UV-vis of PCN membranes was found to display blue shift as the clay loading increased.

碩士
國立清華大學
化學工程學系所
105
This thesis is centered on the self-assembly behavior of nanostructured poly(vinyl alcohol) (PVA) constructed by block copolymer and polymer-surfactant complex. It is further divided into two parts. The first part discusses the self-assembly behavior of PAA-b-PVA block copolymer and PAA/PVA blends. The tensile properties of the block copolymer films were in general much better than those of the corresponding blend, where the maximum fractural tensile stress and strain attained were 27.3 MPa and 641 %. The FTIR study indicated that the extent of hydrogen bonding between PAA and PVA transferred from the solution state could explain the variation of the mechanical properties of a given type of films prepared from the solutions with different pH values, but it was unable to rationalize the large difference between the block copolymer and the blend films prepared under a given pH environment. Combining the results of FTIR spectra, DSC, solution turbidity and SAXS, we proposed that the films composed of the interpolymer complex domains distributed over a matrix phase in which PVA and PAA were phase separated. In the blend films, the phase separation occurred at the macroscopic length scale, generating the PAA and PVA domains of micrometers in size. On the other hand, PVA and PAA blocks in the block copolymer underwent the microphase separation, generating a characteristic nanostructure as evidenced by the SAXS profile. The nanostructure thus formed may prescribe a large amount of interface that led to the considerable enhancement of the tensile properties. In the second part, we studied the self-assembly behavior and phase behavior of polyvinyl alcohol (PVA)/amphiphilic dodecylbenzenesulfonic acid (DBSA) complexes formed by hydrogen bonds. A supramolecular comblike polymer system has been successfully prepared by the complexation of PVA with DBSA via hydrogen bonding. Microphase separation between the polar and nonpolar units generated a lamellar mesophase, as revealed by POM and SAXS. The interlamellar distance increased with decreasing binding fraction of DBSA, indicating that DBSA bound uniformly with PVA backbone. The TODT was found to be largely independent of the binding ratio, which might be due to the occurrence of chemical degradation at elevated temperature.

No
We report on a multiscale polymer-within-polymer structure of the cationic conjugated polyelectrolyte poly{[9,9-bis(6′-N,N,N-trimethylammonium)hexyl]fluorene–phenylene} (HTMA-PFP) in aqueous poly(vinyl alcohol) (PVA) sol. Molecular dynamics simulations and small-angle neutron scattering (SANS) data show that HTMA-PFP forms aggregates in water but becomes entangled by PVA (with a 1:1 molar ratio of HTMA-PFP to PVA) and eventually immersed in PVA clusters (with the ratio 1:4). This is attributed to the hydrophobic–hydrophilic balance. Contrast variation data with regular and deuterated PVA support a rigid body model, where HTMA-PFP is confined as locally isolated, but closely located, chains within PVA clusters, which alter correlation distances within the system. These results are supported by enhanced photoluminescence (PL) and ionic conductivity which, together with a red-shift in UV/vis absorption spectra, indicate the breakup of HTMA-PFP aggregates upon PVA addition.

The choice of the most suitable system for the cleaning of cultural heritage artifacts is a challenging issue due to the great variety of materials and textures that can be encountered during restoration. High control and selectivity are the main features that should characterize an ideal cleaning system. At present, the use of cleaning fluids confined in gelled structures is considered one of the most performing strategies to face concerns related to an excessive penetration of the liquid phase within the porous matrix of the artwork. In the last decades several gel formulations were introduced in restoration practice, most of them pertaining to class of physical gels, while, more recently, also some chemical gel formulations were adopted. Physical gels have usually a jam-like texture and permit to attain homogenous cleaning thanks to their complete adaptability and adhesion to the surface they are put in contact with. However, they present important drawbacks related to left residues after treatment. Chemical gels are characterized by strong cohesion forces, which permit their easy and complete removal and, thus, a residue-free treatment. Their cleaning performances, in terms of homogeneity, might be compromised in case that the irregularities of the surface to be treated don’t permit an appropriate adhesion of the gel. Blended PVA-based hydrogels, obtained through two different synthesis methods, are innovative systems that permit both, homogenous adhesion, thanks to their mechanical adaptability, and an easy and complete removal thanks to strong cohesion forces. Hydrogel synthesis is performed through cast-drying or repeated freezing and thawing of neat or blended PVA aqueous solutions. Gelification process involves the formation of crystalline regions that act as tie- points, contributing to formation of the three-dimensional network. A physico- chemical characterization was carried out on several formulations to investigate synthesis parameters that affect the final properties of the hydrogels. Water content and free water index (FWI) were quantified through thermal analysis (DTG, DSC). The crystallinity degree was determined by means of ATR-FTIR, DSC and XRD. Information about hydrogels porosity were obtained from SEM images, while networks structure was investigated through SAXS analysis. Finally, some preliminary application tests are presented.

碩士
國立臺灣科技大學
纖維及高分子工程研究所
87
Abstract (Part I) PVA[Poly(vinyl-aclohol)] was grafting-copolymerized with SSS(sodium styrenesulfonate) and ammonium cerium(IV) sulfate at 60℃. The SSS content of various copolymers were analyzed with UV-VIS spectroscopy. The water content in hydrogels increases with SSS grafting. The tensile measurements result in the elastic modulus of gels at various temperatures, which yields the crosslink density of hydrogels and Flory-Huggins interaction parameters (χ). Theχparameters decreases with temperature and grafting ratio, and the enthalpic component(χh) decreases with temperatures. The entropic component(χS) decreases with temperature and grafting ratio. The partial molar energy of mixing of water phase decreases with temperatures and grafting ratio. The slip-link model indicates that number of slip-link(or physical entanglement) decreases with temperature and grafting ratio. It is concluded that higher temperature and grafting ratio causes the higher water content, and signifcant disentanglement due to water swelling. The gels are ideal elastomer when the number of slip-link equate zero. It is found that the temperatures at which PVA-g-SSS gels are ideal elastomer decrease with grafting ratio. The swelling ratio of hydrogels increases with the ratio of SSS grafting and crosslink of density due to hydroxyl reactions. Abstract (Part II) An investigation on the influence of ionic contents on interfacial energy was caried out. PVA[Poly(vinyl-aclohol)] grafting-copolymerized with SSS(sodium styrenesulfonate) and ammonium cerium(IV) sulfate at 60℃, as well as PET[poly(ethylene terephalate)] mixture with PETSS(sulphonate sodium-containing PET) were used. The sodium contents of PETSS were analyzed with atomic absorption spectroscopy. The water content of hydrogels and polymer blends increases with ionic sontent. The contact angle of air and n-octane on hydrogels and polymer blends in water at 25℃ were measured. which yield the surface energy of samples(γsv), the dispersion component of surface energy(γdsv), the polar component of surface energy (γpsv) and the water-polymer interfacial energy (γsw). The result imply that the surface energy and the water-polymer interfacial interaction energy (Isw) increases with water content, as well as the water-polymer interfacial energy decreases with water content. Also, the water-gels interfacial energy is corr with Flory-Huggins interactions of polymer-water with fluctuations theory of interface.

碩士
臺灣大學
化學工程學研究所
95
Direct Methanol Fuel Cells (DMFCs) are promising new power sources for vehicles and protable devices. It’s significant challenge to develop proton exchange membranes (PEMs) possing both desired proton conductivity and low methanol permeability for the DMFCs. PEMs currently used in DMFC are perfluorinated polymers such as Nafion®. Even though such membranes have demonstrated good performances and long-term stability, their high cost and methanol crossover makes them unpractical for large-scale production. In this research, I describe two kinds of membranes and discuss respectively. The one is a novel physically and chemically PVA/HFA (PVA/hexafluoroglutaric acid) blending membranes with BASANa (Benzenesulfonic acid sodium salt) and GA (Glutaraldehyde) as binary reaction agents. GA and BASANa were used as cross-linkers and a donor of hydrophilic groups (-SO3H), which they both crosslinked to PVA chains for the acetalization reaction. Besides, HFA with dicarboxylic acid not only as the thermal cross-linking agent but also enhanced the flexibility and chemical stability. The other is to synthesize ampliplilic block copolymers on crosslinked acrylated urethane oligomer using UV-curing method. The amphiphilic block copolymers are synthesized using TEMPO controlled polymerization method with tertrabutylammonium styrenesulfonate (SSTBA) and divinyl benzene (DVB) as monomers for each block. This method has advantage synthesize the copolymer in one organic phase. Crosslinking of membranes of the copolymer are made by adding photo-initiators and subsequently being initiated by using UV light. By mixing acrylated urethane oligomer (AUO) with SSTBA monomer or PSSTBA-b-DVB copolymer and then add the crosslinker TAIC for third component. We can prepare PEM with excellent physicomechanical properties. These properties of the cross-linked PVA/HFA proton-conducting membranes or cross-linked acrylated urethane oligomer with sulfonated styrene membranes are examined by FT-IR/ATR spectroscopy, field emission scanning surface microscopy (FE-SEM), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), atomic force microscopy (AFM), contact angle instrument, sorption studies, tensile test and AC impedance method. The feasibility of preparing films for DMFC application is investigated in this study. The proton conductivities and the methanol permeabilities of all two kinds of the membranes are in the range of 10-4 to 10-2 S/cm and 10-8 to 10-7 cm2/s, respectively, depending on its crosslinking density, and it shows great selectivity (Φ) compared with those of Nafion®-117. The possibility of using these PEMs for DMFC device is suggested.

碩士
國立臺灣科技大學
高分子工程系
92
Polyvinyl alcohol gels crosslinked with sodium styrenesulfonate（SSS） with SSS grafting ratio from 1.3×10-3 to 3.5×10-3 were prepared and drugs（Benzoic acid , Vitamin K3 and Caffeine）permeation and diffusion through gels were determined. The mesh size of gels were determined with hydrogel water contents（swelling）and elasticity data. The diffusion coefficients increase with swelling, and the solubility increases with drug size. Diffusion coefficient and solubility were presented in terms of the ratio of drug diameter to that of mesh size. The diffusion is a controlling step driving the permeation. The tortuosity of drug diffusion data in gels was calculated, which is significantly greater than the predicted value from the transport model in rigid porous media. This deviation is due to the complex structure of gels. Solute diffusion data are fitted with free volume model. We found that the slope of solute diffusion data versus the reciprocal of free volume is smaller than free volume estimation from the relation of ln（D/D0） and （1/H-1）. In the hydrogels, the steady-state adsorption factors of the solutes with higher solubility is smaller than the solute with lower solubility. The initial adsorption factors increase with SSS grafting ratio, because SSS have ionic groups interacting with the solutes. The adsorption increase with the mesh size，and the surface adsorption has greater effect for the solute with lower solubility.

Cultural Heritage assets are crucial to mankind, as they are drivers of welfare and economic improvement. If properly preserved, this patrimony can boost job creation, social inclusion, and cultural identity. Unfortunately, degradation processes inevitably threaten works of art. Colloids and material science have been providing effective solutions to preserve works of art in the last decades. In the specific case of cleaning of painted artworks, excellent results have been obtained using highly performing gels based on synthetic polymers like poly (vinyl pyrrolidone) (PVP) and poly (hydroxyethyl methacrylate) (pHEMA). However, there is still large room for the formulation of polymer networks that retain optimal cleaning ability but have higher eco-compatibility. In this perspective, we have developed and studied different biocomposite hydrogels based on poly(vinyl alcohol) (PVA) and rice starch (RS) obtained via freeze-thawing, with water as the only used solvent. The PVA/RS hydrogels have been extensively characterized from a morphological, rheological, and structural point of view and have been tested as cleaning tools on painted mock-ups with excellent outcomes, showing performances comparable with their state-of-the-art synthetic counterparts. Furthermore, the introduction of a biopolymer in the synthetic path improved the sustainability of the art cleaning formulations, while maintaining optimal and tunable mechanical behavior. Besides, the reduction of usage and disposal of materials based on synthetic polymers is an urgent and transversal need, and biocomposite PVA/starch-based systems could meet the requirements that different applications demand., being broadly tunable by simply varying the PVA:starch ratio in their formulation. Nevertheless, starch as a raw product comes with a high variety of features, especially regarding the composition of its polymeric portion (i.e., the amylose to amylopectin ratio), which is cardinal in determining the properties of the biocomposite systems. The investigation of the fundamental interactions between PVA, amylose, and amylopectin has therefore been deemed necessary to set a reliable base from which to start developing state-of- the-art materials, drastically reducing the usage of synthetic reagents without compromises in terms of performances. Said mutual interactions and their consequences have been investigated by means of direct laser imaging of fluorescently labeled systems, thermal analysis, and Small-Angle X-ray Scattering, coupling the results with rheological measurements and gel fraction trends to provide a preliminary theoretical framework, the aim of which is to support future developments of highly performing eco-sustainable materials.

abstract: Polymer fibers have broad applications in wearable electronics, bulletproof vests, batteries, fuel cells, filters, electrodes, conductive wires, and biomedical materials. Polymer fibers display light density and flexibility but are mostly weak and compliant. The ceramic, metallic, and carbon nanoparticles have been frequently included in polymers for fabricating continuous, durable, and functional composite fibers. Nanoparticles display large specific areas, low defect density and can transfer their superior properties to polymer matrices. The main focus of this thesis is to design, fabricate and characterize the polymer/nanocarbon composite fibers with unique microstructures and improved mechanical/thermal performance. The dispersions and morphologies of graphene nanoplatelets (GNPs), the interactions with polyvinyl alcohol (PVA) molecules and their influences on fiber properties are studied. The fibers were fabricated using a dry-jet wet spinning method with engineered spinneret design. Three different structured fibers were fabricated, namely, one-phase polymer fiber (1-phase), two-phase core-shell composite fiber (2-phase), and three-phase co-axial composite fiber (3-phase). These polymer or composite fibers were processed at three stages with drawing temperatures of 100˚C, 150˚C, and 200˚C. Different techniques including the mechanical tester, wide-angle X-Ray diffraction (WAXD), scanning electron microscope (SEM), thermogravimetric analysis (TGA), and differential scanning calorimeter (DSC) have been used to characterize the fiber microstructures and properties.
Dissertation/Thesis
Masters Thesis Mechanical Engineering 2018

Dissertação de mestrado integrado em Engenharia de Polímeros
A aplicação de cargas em polímeros, tais como grafite, nanotubos de carbono, fulerenos e mais recentemente o grafeno, tem atraído a atenção de investigadores que procuram a produção de materiais compósitos com propriedades especiais. Para melhorar as propriedades, sobretudo mecânicas, elétricas e térmicas, dos compósitos tem sido estudada a incorporação destas em polímeros e a sua influência sobre as propriedades dos compósitos resultantes. Neste trabalho estudou-se a influência da incorporação de grafite e grafeno em poli(álcool vinílico) (PVA), com o objetivo de produzir filmes de PVA e seus compósitos com propriedades melhoradas. Deste modo, foram produzidos filmes compósitos com PVA e grafite, assim como grafite exfoliada, preparados por uma técnica de mistura em solução. As soluções de grafite exfoliada foram preparadas pela técnica de funcionalização não-covalente em solução aquosa. Foi estimada uma incorporação até 10 wt% de grafite como reforço. As propriedades mecânicas dos filmes foram avaliadas por ensaios de tração uniaxial e foram medidas as propriedades elétricas. Em relação à condutividade elétrica, os valores aumentaram com a incorporação de grafite na matriz polimérica. O contrário sucedeu-se nas propriedades mecânicas que não foram melhoradas, pois os filmes tornaram-se mais frágeis. As caraterísticas térmicas e a estabilidade térmica dos filmes foram avaliadas por calorimetria diferencial de varrimento (DSC) e análise termogravimétrica (TGA), respetivamente. Os resultados de DSC revelaram que a incorporação de cargas não influenciou as temperaturas de transição vítrea e fusão e não tem um efeito significativo no grau de cristalinidade. No entanto, a partir do ensaio de TGA indicou que a adição de grafite pode levar a um atraso da degradação térmica. Por fim, foi também realizada a análise de microscopia eletrónica de varrimento (SEM) e de permeabilidade ao vapor de água dos filmes produzidos. As imagens SEM revelaram uma boa interface entre o polímero e a matriz polimérica. Relativamente ao ensaio de permeabilidade os filmes compósitos com grafite demonstraram ter um comportamento semelhante à matriz.
The application of fillers in polymers, as graphite, carbon nanotubes, fullerenes and more recently graphene, has attracted the attention of researchers seeking the production of composite materials with special properties. To improve the properties of composite materials, mainly mechanical, electrical and thermal, the incorporation of these and their influence on the properties of resulting composites have been studied. In this work it was studied the influence of the incorporation of graphite and graphene in poly(vinyl alcohol) (PVA), with the purpose of producing PVA films and their composites with improved properties. In this way, composite films with PVA and graphite were produced, as well as exfoliated graphite, prepared by a mixing technique in solution. The exfoliated graphite solutions were prepared by the non-covalent functionalization technique in aqueous solution. It was estimated an incorporation of up to 10 wt% of graphite as reinforcement. The mechanical properties of the films were evaluated by uniaxial tensile tests and the electrical properties were measured. As regards the electrical conductivity, the values increased with the incorporation of graphite in the polymeric matrix. The opposite was observed in mechanical properties, which weren’t improved, since the films became more fragile. The thermal characteristics and the thermal stability of the films were evaluated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The DSC results revealed that the incorporation of fillers didn’t influenced the glass transition and fusion temperatures and didn’t have a significant effect on the degree of crystallinity. However, from the TGA test it was possible to conclude that the addition of graphite may lead to a delay of thermal degradation. At last, it were also performed the analysis of scanning electronic microscopy (SEM) and water vapour permeability of the films produced. The SEM images revealed a good interface between the filler and the polymeric matrix. Concerning the water vapour permeability test, the composite films with graphite showed a similar behaviour to the matrix.

碩士
長庚大學
化工與材料工程研究所
93
Interpenetrating network membranes of poly (2-hydroxylethyl meth- acrylate) (poly HEMA) and poly (vinyl alcohol) (PVA) in various ratios were prepared by UV radiation and treated with glutaraldehyde (GA). From the spectral change of FTIR, the hydroxyl groups disappeared and an acetal ring and ether linkage were formed for the reaction between the hydroxyl groups of PVA and GA. From the stress-strain curve, it was found that the tensile strength and elongation increased with PVA content on the PVA / poly (HEMA) membranes. After crosslinking with GA, the membranes became brittle, whereas the thermal stability increased about 20-100℃. Two glass transition temperature were found for the PVA / poly (HEMA) membranes. It means that PVA and poly (HEMA) are incompatible in this study. Due to the hydrophilicity of poly (HEMA), the water content in the membranes increased with increasing the content of poly (HEMA) in the membranes. After treatment with GA, the contact angle on the PVA / poly (HEMA) membranes decreased. The permeation of creatinine, 5-fluorouracil (5-FU) and vitamin B12 through at 37℃ were conducted. The permeability increased with increasing poly (HEMA) content in the membranes.

Dissertação de Mestrado Integrado em Engenharia Química apresentada à Faculdade de Ciências e Tecnologia
Nos últimos anos uma crescente preocupação ambiental tem guiado parte da investigação científica no sentido de desenvolver soluções mais eficientes e económicas para a captura, separação e armazenamento de dióxido de carbono (CO2). Neste contexto e de entre as tecnologias que mais têm crescido nestes últimos anos, os processos de separação seletiva de CO2 através de membranas de base polimérica ou compósita, têm-se vindo a destacar, principalmente devido à sua versatilidade, caráter limpo e baixo custo. No entanto e em alguns casos específicos, a sua baixa eficiência e baixa capacidade de produção podem tornar estes processos menos competitivos quando comparados com outros processos de separação de CO2. Assim, de entre outras abordagens e no sentido de fazer face a estas limitações, algumas das estratégias desenvolvidas recentemente têm-se focado na preparação de membranas com elevada seletividade para o CO2, o que tem vindo a ser feito através da incorporação de certos aditivos com grande afinidade para este gás nos materiais que compõem as membranas de separação gasosa. De entre estes aditivos a incorporação de determinados líquidos iónicos (LI) ou poli(líquidos iónicos) (PIL), muito específicos, tem vindo a ser considerada e estudada nos últimos anos uma vez que estas substâncias são conhecidas pela sua elevada capacidade em absorver quantidades apreciáveis de CO2. No entanto, a incorporação destes LI em membranas de separação gasosa em geral, e de CO2 em particular, necessita ainda de ser melhorada de forma a evitar, entre outros problemas, a segregação de fases. Desta forma torna-se necessário desenvolver novos materiais e novas estratégias de incorporação destes compostos em membranas de separação de CO2. Este trabalho tem como principal objetivo a síntese, o processamento e a caracterização de membranas compósitas com potencial para serem usadas na captura e separação de CO2, e que consistem numa matriz polimérica, de base poli(álcool vinílico) (PVA), não-reticuladas ou reticuladas com glutaraldeído (GA), não plastificadas ou plastificadas com glicerol, e que contêm micro/nano cápsulas de sílica (shell)/LI(core) imobilizadas no seu interior. Devido ao seu carácter hidrofóbico e à sua capacidade de solubilizar quantidades apreciáveis de CO2, o LI escolhido e usado neste trabalho foi o 3Methyl-1-Octylimidazolium bis(trifluoromethylsulfonyl)imide (OMIM[NTf2]).
In recent years a growing environmental concern has guided part of scientific research to develop more efficient and economical solutions for the capture, separation and storage of carbon dioxide (CO2). In this context, and among the technologies that have grown the most in recent years, the processes of selective separation of CO2 through polymer-based or composite-based membranes have come to the fore, mainly due to their versatility, clean character and low cost. However, and in some specific cases, their low efficiency and low production capacity may render these processes less competitive when compared to other CO2 separation processes. Thus, among other approaches and to address these limitations, some of the strategies developed recently have focused on the preparation of membranes with high selectivity for CO2, which has been done through the incorporation of certain additives with high affinity for this gas in the materials that make up the gas separation membranes. Among these additives, the incorporation of certain very specific ionic liquids (IL) or poly (liquid ionics) (PIL) has been considered and studied in recent years as these substances are known for their high capacity to absorb significant quantities of CO2. However, the incorporation of these ILs into gas separation membranes in general, and CO2 in particular, still needs to be improved in order to avoid, among other problems, the ionic liquid loss. In this way it would be necessary to develop new materials and new strategies of incorporation of these compounds into CO2 separation membranes. This work has as main objective the synthesis, processing and characterization of composite membranes with potential to be used in the capture and separation of CO2, and which consist of a poly (vinyl alcohol) (PVA) based matrix crosslinked with glutaraldehyde (GA), unplasticized or plasticized with glycerol, and containing micro/nano silica (shell)/LI (core) capsules. Due to its hydrophobic character and to its ability to solubilize appreciable amounts of CO2, the IL chosen and used for this work is the 3-Methyl-1-Octylimidazolium bis (trifluoromethylsulfonyl) imide (OMIM [NTf2]).

In recent years, electrochemical capacitors have emerged as devices with the potential to enable major advances in electrical energy storage. Electrochemical capacitors (ECs) are akin to conventional capacitors but employ higher surface-area electrodes and thinner dielectrics to achieve larger capacitances. This helps ECs to attain energy densities greater than those of conventional capacitors and power densities greater than those of batteries. Akin to conventional capacitors, ECs also have high cycle-lives and can be charged and discharged rapidly. But ECs are yet to match the energy densities of mid to high-end batteries and fuel cells. On the basis of mechanism involved in the charge-storage process, ECs are classified as electrical double-layer capacitors (EDLCs) or pseudocapacitors. Charge storage in EDLCs and pseudocapacitors is brought about by non-faradaic and faradaic processes, respectively. Faradaic process, such as an oxidation-reduction reaction, involves the transfer of charge between electrode and electrolyte. By contrast, a non-faradaic process does not use a chemical mechanism and charges are distributed on surfaces by physical processes that do not involve any chemical reaction. ECs employ both aqueous and non-aqueous electrolytes in either liquid or solid form, the latter providing the advantages of freedom from leakage of any liquid component, compactness, reliability and large operating potential-window. In the literature, polymer electrolytes are the most widely studied solid electrolytes. Complexation of functional-groups of certain polymers with cations results in the formation of polymer-cation complexes commonly referred to as solid-polymer electrolytes (SPEs). Mixing a polymer with an alkali metal salt dissolved in an organic solvent result in the formation of a polymer gel electrolyte. Organic solvents with low molecular-weights, such as ethylene carbonate and propylene carbonate, employed in polymer gel electrolytes are commonly referred to as plasticizers. When water is used as a plasticizer, the polymer electrolyte is called a polymer hydrogel electrolyte. Part I of the thesis is directed to studies pertaining to Polymer Hydrogel Electrolytes for Electrochemical Capacitors and comprises four sections. After a brief survey of literature on polymer hydrogel electrolytes employed in ECs in Section I.1, Section I.2 of Part I describes the studies on electrochemical capacitors employing cross-linked poly (vinyl alcohol) hydrogel membrane electrolytes with varying perchloric acid dopant concentration. Acidic poly (vinyl alcohol) hydrogel membrane electrolytes (PHMEs) with different perchloric acid concentrations are prepared by cross-linking poly (vinyl alcohol) with glutaraldehyde in the presence of a protonic acid acting as a catalyst under ambient conditions. PHMEs are characterized by scanning electron microscopy and temperature-modulated differential scanning calorimetry in conjunction with relevant electrochemical techniques. An optimised electrochemical capacitor assembled employing PHME in conjunction with black pearl carbon (BPC) electrodes yields a maximum specific capacitance value of about 96 F g-1, phase angle value of about 79o and a discharge capacitance value of about 88 F g-1. Section I.3 of Part I describes the studies on cross-linked poly (vinyl alcohol)/ploy (acrylic acid) blend hydrogel electrolytes for electrochemical capacitors. Acidic poly (vinyl alcohol)/poly (acrylic acid) blend hydrogel electrolytes (BHEs) have been prepared by cross-linking poly (vinyl alcohol)/poly (acrylic acid) blend with glutaraldehyde in presence of perchloric acid. These acidic BHEs have been treated suitably to realize alkaline and neutral BHEs. Thermal characteristics and glass-transition behavior of BHEs have been followed by differential scanning calorimetry. Ionic conduction in acidic BHEs has been found to take place by Grötthus-type mechanism while polymer segmental motion mechanism is predominantly responsible for ion motion in alkaline and neutral BHEs. Ionic conductivity of BHEs has been found to range between 10-3 and 10-2 S cm-1 at 298 K. Electrochemical capacitors assembled with acidic PVA hydrogel electrolyte yield a maximum specific capacitance of about 60 and 1000 F g-1 with BPC and RuOx.xH2O/C electrodes, respectively. Section I.4 of Part I describes the studies on gelatin hydrogel electrolytes and their application to electrochemical capacitors. Gelatin hydrogel electrolytes (GHEs) with varying NaCl concentrations have been prepared by cross-linking an aqueous solution of gelatin with aqueous glutaraldehyde under ambient conditions, and characterized by scanning electron microscopy, temperature-modulated differential scanning calorimetry, cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic chronopotentiometry. Glass transition temperatures for GHEs range between 340 and 377 K depending on the dopant concentration. Ionic conductivity behavior of GHEs is studied with varying concentrations of gelatin, glutaraldehyde and NaCl, and conductivity values are found to vary between 10-3 and 10-1 S cm-1 under ambient conditions. GHEs have a potential window of about 1 V with BPC electrodes. The ionic conductivity of pristine and 0.25 N NaCl-doped GHEs follows Arrhenius behavior with activation energy values of 1.9×10-4 and 1.8×10-4 eV, respectively. Electrochemical capacitors employing GHEs in conjunction with black pearl carbon electrodes are assembled and studied. Optimal values for capacitance, phase angle, and relaxation time constant of about 81 F g-1, 75o, and 0.03 s are obtained for 3 M NaCl-doped GHE, respectively. EC with pristine GHE exhibits continuous cycle life for about 4.3 h as against 4.7 h for the electrochemical capacitor with 3 M NaCl-doped GHE. Unlike electrochemical capacitors, fuel cells do not store the charge internally but instead use a continuous supply of fuel from an external storage tank. Thus, fuel cells have the potential to solve the most challenging problem associated with the electrochemical capacitors, namely their limited energy-density. A fuel cell is an electrochemical power source with advantages of both the combustion engine and the battery. Like a combustion engine, a fuel cell will run as long as it is provided with fuel; and like a battery, fuel cells convert chemical energy directly to electrical energy. As an electrochemical power source, fuel cells are not subjected to the Carnot limitations of combustion (heat) engines. A fuel cell operates quietly and efficiently and, when hydrogen is used as a fuel, it generates only power and potable water. Thus, a fuel cell is a so called ‘zero-emission engine’. In the past, several fuel cell concepts have been tested in various laboratories but the systems that are being potentially considered for commercial developments are: (i) Alkaline Fuel Cells (AFCs), (ii) Phosphoric Acid Fuel Cells (PAFCs), (iii) Polymer Electrolyte Fuel Cells (PEFCs), (iv) Solid-Polymer-Electrolyte-Direct Methanol Fuel Cells (SPE-DMFCs), (v) Molten Carbonate Fuel Cells (MCFCs) and (vi) Solid Oxide Fuel Cells (SOFCs). Among the aforesaid systems, PEFCs that employ hydrogen as fuel are considered attractive power systems for quick start-up and ambient-temperature operations. Ironically, however, hydrogen as fuel is not available freely in the nature. Accordingly, it has to be generated from a readily available hydrogen carrying fuel such as natural gas, which needs to be reformed. But, such a process leads to generation of hydrogen with some content of carbon monoxide, which even at minuscule level is detrimental to the fuel cell performance. Pure hydrogen can be generated through water electrolysis but hydrogen thus generated needs to be stored as compressed / liquefied gas, which is cost-intensive. Therefore, certain hydrogen carrying organic fuels such as methanol, ethanol, propanol, ethylene glycol, and diethyl ether have been considered for fuelling PEFCs directly. Among these, methanol with a hydrogen content of about 13 wt. % (specific energy = 6.1 kWh kg-1) is the most attractive organic liquid. PEFCs using methanol directly as fuel are referred to as SPE-DMFCs. But SPE-DMFCs suffer from methanol crossover across the polymer electrolyte membrane, which affects the cathode performance and hence the cell performance during its operation. SPE-DMFCs also have inherent limitations of low open-circuit-potential and low electrochemical-activity. An obvious solution to the aforesaid problems is to explore other promising hydrogen carrying fuels such as sodium borohydride, which has a hydrogen content of about 11 wt. %. Such fuel cells are called direct borohydride fuel cells (DBFCs). Part II of the thesis includes studies on direct borohydride fuel cells and comprises three sections. After a brief introduction to DBFCs in section II.1, Section II.2 describes studies on an alkaline direct borohydride fuel cell with hydrogen peroxide as oxidant. A peak power density of about 150 mW cm-2 at a cell voltage of 540 mV could be achieved from the optimized DBFC operating at 70oC. Section II.3 describes studies on poly (vinyl alcohol) hydrogel membrane as electrolyte for direct borohydride fuel cells. This DBFC employs a poly (vinyl alcohol) hydrogel membrane as electrolyte, an AB5 Misch metal alloy as anode, and a gold-plated stainless steel mesh as cathode in conjunction with aqueous alkaline solution of sodium borohydride as fuel and aqueous acidified solution of hydrogen peroxide as oxidant. The performance of the PHME-based DBFC in respect of peak power outputs, ex-situ cross-over of oxidant, fuel, anolyte and catholyte across the membrane electrolytes, utilization efficiencies of fuel and oxidant as also cell performance durability under ambient conditions are compared with a similar DBFC employing a Nafion®-117 membrane electrolyte (NME). Peak power densities of about 30 and 40 mW cm-2 are observed for the DBFCs with PHME and NME, respectively. The PHME and NME-based DBFCs exhibit cell potentials of about 1.2 and 1.4 V, respectively, at a load current density of 10 mA cm-2 for 100 h. Publications of Nurul Alam Choudhury 1. Gelatin hydrogel electrolytes and their application to electrochemical supercapacitors, N. A. Choudhury, S. Sampath, and A. K. Shukla, J. Electrochem. Soc., 155 (2008) A74. 2. Cross-linked polymer hydrogel electrolytes for electrochemical capacitors, N. A. Choudhury, A. K. Shukla, S. Sampath, and S. Pitchumani, J. Electrochem. Soc., 153 (2006) A614. 3. Hydrogel-polymer electrolytes for electrochemical capacitors: an overview, N. A. Choudhury, S. Sampath, and A. K. Shukla, Energy and Environmental Science (In Press). 4. Cross-linked poly (vinyl alcohol) hydrogel membrane electrolytes with varying perchloric acid dopant concentration and their application to electrochemical capacitors, N. A. Choudhury, S. Sampath, and A. K. Shukla, J. Chem. Sc. (Submitted) 5. An alkaline direct borohydride fuel cell with hydrogen peroxide as oxidant, N. A. Choudhury, R. K. Raman, S. Sampath, and A. K. Shukla, J. Power Sources, 143 (2005) 1. 6. Poly (vinyl alcohol) hydrogel membrane as electrolyte for direct borohydride fuel cells, N. A. Choudhury, S. K. Prashant, S. Pitchumani, P. Sridhar, and A. K. Shukla, J. Chem. Sc. (Submitted). 7. A phenyl-sulfonic acid anchored carbon-supported platinum catalyst for polymer electrolyte fuel cell electrodes, G. Selvarani, A. K. Sahu, N. A. Choudhury, P. Sridhar, S. Pitchumani, and A. K. Shukla, Electrochim. Acta, 52 (2007) 4871. 8. A high-output voltage direct borohydride fuel cell, R. K. Raman, N. A. Choudhury, and A. K. Shukla, Electrochem. Solid-State Lett., 7 (2004) A 488. 9. Carbon-supported Pt-Fe alloy as a methanol-resistant oxygen-reduction catalyst for direct methanol fuel cells, A. K. Shukla, R. K. Raman, N. A. Choudhury, K. R. Priolkar, P. R. Sarode, S. Emura, and R. Kumashiro, J. Electroanal. Chem., 563 (2004) 181.

In recent years, electrochemical capacitors have emerged as devices with the potential to enable major advances in electrical energy storage. Electrochemical capacitors (ECs) are akin to conventional capacitors but employ higher surface-area electrodes and thinner dielectrics to achieve larger capacitances. This helps ECs to attain energy densities greater than those of conventional capacitors and power densities greater than those of batteries. Akin to conventional capacitors, ECs also have high cycle-lives and can be charged and discharged rapidly. But ECs are yet to match the energy densities of mid to high-end batteries and fuel cells. On the basis of mechanism involved in the charge-storage process, ECs are classified as electrical double-layer capacitors (EDLCs) or pseudocapacitors. Charge storage in EDLCs and pseudocapacitors is brought about by non-faradaic and faradaic processes, respectively. Faradaic process, such as an oxidation-reduction reaction, involves the transfer of charge between electrode and electrolyte. By contrast, a non-faradaic process does not use a chemical mechanism and charges are distributed on surfaces by physical processes that do not involve any chemical reaction. ECs employ both aqueous and non-aqueous electrolytes in either liquid or solid form, the latter providing the advantages of freedom from leakage of any liquid component, compactness, reliability and large operating potential-window. In the literature, polymer electrolytes are the most widely studied solid electrolytes. Complexation of functional-groups of certain polymers with cations results in the formation of polymer-cation complexes commonly referred to as solid-polymer electrolytes (SPEs). Mixing a polymer with an alkali metal salt dissolved in an organic solvent result in the formation of a polymer gel electrolyte. Organic solvents with low molecular-weights, such as ethylene carbonate and propylene carbonate, employed in polymer gel electrolytes are commonly referred to as plasticizers. When water is used as a plasticizer, the polymer electrolyte is called a polymer hydrogel electrolyte. Part I of the thesis is directed to studies pertaining to Polymer Hydrogel Electrolytes for Electrochemical Capacitors and comprises four sections. After a brief survey of literature on polymer hydrogel electrolytes employed in ECs in Section I.1, Section I.2 of Part I describes the studies on electrochemical capacitors employing cross-linked poly (vinyl alcohol) hydrogel membrane electrolytes with varying perchloric acid dopant concentration. Acidic poly (vinyl alcohol) hydrogel membrane electrolytes (PHMEs) with different perchloric acid concentrations are prepared by cross-linking poly (vinyl alcohol) with glutaraldehyde in the presence of a protonic acid acting as a catalyst under ambient conditions. PHMEs are characterized by scanning electron microscopy and temperature-modulated differential scanning calorimetry in conjunction with relevant electrochemical techniques. An optimised electrochemical capacitor assembled employing PHME in conjunction with black pearl carbon (BPC) electrodes yields a maximum specific capacitance value of about 96 F g-1, phase angle value of about 79o and a discharge capacitance value of about 88 F g-1. Section I.3 of Part I describes the studies on cross-linked poly (vinyl alcohol)/ploy (acrylic acid) blend hydrogel electrolytes for electrochemical capacitors. Acidic poly (vinyl alcohol)/poly (acrylic acid) blend hydrogel electrolytes (BHEs) have been prepared by cross-linking poly (vinyl alcohol)/poly (acrylic acid) blend with glutaraldehyde in presence of perchloric acid. These acidic BHEs have been treated suitably to realize alkaline and neutral BHEs. Thermal characteristics and glass-transition behavior of BHEs have been followed by differential scanning calorimetry. Ionic conduction in acidic BHEs has been found to take place by Grötthus-type mechanism while polymer segmental motion mechanism is predominantly responsible for ion motion in alkaline and neutral BHEs. Ionic conductivity of BHEs has been found to range between 10-3 and 10-2 S cm-1 at 298 K. Electrochemical capacitors assembled with acidic PVA hydrogel electrolyte yield a maximum specific capacitance of about 60 and 1000 F g-1 with BPC and RuOx.xH2O/C electrodes, respectively. Section I.4 of Part I describes the studies on gelatin hydrogel electrolytes and their application to electrochemical capacitors. Gelatin hydrogel electrolytes (GHEs) with varying NaCl concentrations have been prepared by cross-linking an aqueous solution of gelatin with aqueous glutaraldehyde under ambient conditions, and characterized by scanning electron microscopy, temperature-modulated differential scanning calorimetry, cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic chronopotentiometry. Glass transition temperatures for GHEs range between 340 and 377 K depending on the dopant concentration. Ionic conductivity behavior of GHEs is studied with varying concentrations of gelatin, glutaraldehyde and NaCl, and conductivity values are found to vary between 10-3 and 10-1 S cm-1 under ambient conditions. GHEs have a potential window of about 1 V with BPC electrodes. The ionic conductivity of pristine and 0.25 N NaCl-doped GHEs follows Arrhenius behavior with activation energy values of 1.9×10-4 and 1.8×10-4 eV, respectively. Electrochemical capacitors employing GHEs in conjunction with black pearl carbon electrodes are assembled and studied. Optimal values for capacitance, phase angle, and relaxation time constant of about 81 F g-1, 75o, and 0.03 s are obtained for 3 M NaCl-doped GHE, respectively. EC with pristine GHE exhibits continuous cycle life for about 4.3 h as against 4.7 h for the electrochemical capacitor with 3 M NaCl-doped GHE. Unlike electrochemical capacitors, fuel cells do not store the charge internally but instead use a continuous supply of fuel from an external storage tank. Thus, fuel cells have the potential to solve the most challenging problem associated with the electrochemical capacitors, namely their limited energy-density. A fuel cell is an electrochemical power source with advantages of both the combustion engine and the battery. Like a combustion engine, a fuel cell will run as long as it is provided with fuel; and like a battery, fuel cells convert chemical energy directly to electrical energy. As an electrochemical power source, fuel cells are not subjected to the Carnot limitations of combustion (heat) engines. A fuel cell operates quietly and efficiently and, when hydrogen is used as a fuel, it generates only power and potable water. Thus, a fuel cell is a so called ‘zero-emission engine’. In the past, several fuel cell concepts have been tested in various laboratories but the systems that are being potentially considered for commercial developments are: (i) Alkaline Fuel Cells (AFCs), (ii) Phosphoric Acid Fuel Cells (PAFCs), (iii) Polymer Electrolyte Fuel Cells (PEFCs), (iv) Solid-Polymer-Electrolyte-Direct Methanol Fuel Cells (SPE-DMFCs), (v) Molten Carbonate Fuel Cells (MCFCs) and (vi) Solid Oxide Fuel Cells (SOFCs). Among the aforesaid systems, PEFCs that employ hydrogen as fuel are considered attractive power systems for quick start-up and ambient-temperature operations. Ironically, however, hydrogen as fuel is not available freely in the nature. Accordingly, it has to be generated from a readily available hydrogen carrying fuel such as natural gas, which needs to be reformed. But, such a process leads to generation of hydrogen with some content of carbon monoxide, which even at minuscule level is detrimental to the fuel cell performance. Pure hydrogen can be generated through water electrolysis but hydrogen thus generated needs to be stored as compressed / liquefied gas, which is cost-intensive. Therefore, certain hydrogen carrying organic fuels such as methanol, ethanol, propanol, ethylene glycol, and diethyl ether have been considered for fuelling PEFCs directly. Among these, methanol with a hydrogen content of about 13 wt. % (specific energy = 6.1 kWh kg-1) is the most attractive organic liquid. PEFCs using methanol directly as fuel are referred to as SPE-DMFCs. But SPE-DMFCs suffer from methanol crossover across the polymer electrolyte membrane, which affects the cathode performance and hence the cell performance during its operation. SPE-DMFCs also have inherent limitations of low open-circuit-potential and low electrochemical-activity. An obvious solution to the aforesaid problems is to explore other promising hydrogen carrying fuels such as sodium borohydride, which has a hydrogen content of about 11 wt. %. Such fuel cells are called direct borohydride fuel cells (DBFCs). Part II of the thesis includes studies on direct borohydride fuel cells and comprises three sections. After a brief introduction to DBFCs in section II.1, Section II.2 describes studies on an alkaline direct borohydride fuel cell with hydrogen peroxide as oxidant. A peak power density of about 150 mW cm-2 at a cell voltage of 540 mV could be achieved from the optimized DBFC operating at 70oC. Section II.3 describes studies on poly (vinyl alcohol) hydrogel membrane as electrolyte for direct borohydride fuel cells. This DBFC employs a poly (vinyl alcohol) hydrogel membrane as electrolyte, an AB5 Misch metal alloy as anode, and a gold-plated stainless steel mesh as cathode in conjunction with aqueous alkaline solution of sodium borohydride as fuel and aqueous acidified solution of hydrogen peroxide as oxidant. The performance of the PHME-based DBFC in respect of peak power outputs, ex-situ cross-over of oxidant, fuel, anolyte and catholyte across the membrane electrolytes, utilization efficiencies of fuel and oxidant as also cell performance durability under ambient conditions are compared with a similar DBFC employing a Nafion®-117 membrane electrolyte (NME). Peak power densities of about 30 and 40 mW cm-2 are observed for the DBFCs with PHME and NME, respectively. The PHME and NME-based DBFCs exhibit cell potentials of about 1.2 and 1.4 V, respectively, at a load current density of 10 mA cm-2 for 100 h. Publications of Nurul Alam Choudhury 1. Gelatin hydrogel electrolytes and their application to electrochemical supercapacitors, N. A. Choudhury, S. Sampath, and A. K. Shukla, J. Electrochem. Soc., 155 (2008) A74. 2. Cross-linked polymer hydrogel electrolytes for electrochemical capacitors, N. A. Choudhury, A. K. Shukla, S. Sampath, and S. Pitchumani, J. Electrochem. Soc., 153 (2006) A614. 3. Hydrogel-polymer electrolytes for electrochemical capacitors: an overview, N. A. Choudhury, S. Sampath, and A. K. Shukla, Energy and Environmental Science (In Press). 4. Cross-linked poly (vinyl alcohol) hydrogel membrane electrolytes with varying perchloric acid dopant concentration and their application to electrochemical capacitors, N. A. Choudhury, S. Sampath, and A. K. Shukla, J. Chem. Sc. (Submitted) 5. An alkaline direct borohydride fuel cell with hydrogen peroxide as oxidant, N. A. Choudhury, R. K. Raman, S. Sampath, and A. K. Shukla, J. Power Sources, 143 (2005) 1. 6. Poly (vinyl alcohol) hydrogel membrane as electrolyte for direct borohydride fuel cells, N. A. Choudhury, S. K. Prashant, S. Pitchumani, P. Sridhar, and A. K. Shukla, J. Chem. Sc. (Submitted). 7. A phenyl-sulfonic acid anchored carbon-supported platinum catalyst for polymer electrolyte fuel cell electrodes, G. Selvarani, A. K. Sahu, N. A. Choudhury, P. Sridhar, S. Pitchumani, and A. K. Shukla, Electrochim. Acta, 52 (2007) 4871. 8. A high-output voltage direct borohydride fuel cell, R. K. Raman, N. A. Choudhury, and A. K. Shukla, Electrochem. Solid-State Lett., 7 (2004) A 488. 9. Carbon-supported Pt-Fe alloy as a methanol-resistant oxygen-reduction catalyst for direct methanol fuel cells, A. K. Shukla, R. K. Raman, N. A. Choudhury, K. R. Priolkar, P. R. Sarode, S. Emura, and R. Kumashiro, J. Electroanal. Chem., 563 (2004) 181.

This doctoral dissertation takes the reader through a journey where applied shear rheology and flow-velocimetry are used to understand the mesoscopic factors that control the flow behavior of three microstructured fluids. Three individual protocols that measure relative physical and mechanical properties of the flow are developed. Each protocol aims to advance the particular transformation of novel soft materials into a commercial product converging in the demonstration of the real the chemical, physical and thermodynamical factors that could potentially drive their successful transformation.

First, this dissertation introduces the use of rotational and oscillatory shear rheometry to quantify the solvent evaporation effect on the flow behavior of polymer solutions used to fabricate isoporous asymmetric membranes. Three different A-B-C triblock copolymer were evaluated: polyisoprene-b-polystyrene-b-poly(4-vinylpyridine) (ISV); polyisoprene-b-polystyrene-b-poly(N,N-dimethylacrylamide) (ISD); and polyisoprene-b-polystyrene-b-poly(tert-butyl methacrylate) (ISB). The resulting evaporation-induced microstructure showed a solution viscosity and film viscoelasticity strongly dependent on the chemical structure of the triblock copolymer molecules.

Furthermore, basic shear rheometry, flow birefringence, and advanced flow-velocimetry are used to deconvolute the flow-microstructure relationships of concentrated surfactant solutions. Sodium laureth sulfate in water (SLE₁S) was used to replicate spherical, worm-like, and hexagonally packed micelles and lamellar structures. Interesting findings demonstrated that regular features of flow curves, such as power-law shear thinning behavior, resulted from a wide variety of experimental artifacts that appeared when measuring microstructured fluids with shear rheometry.

Finally, the successful integration of shear rheometry to calculate essential parameters to be used in a cost-effective visualization technique (still in development) used to calculate the dissolution time of polymers is addressed. The use of oscillatory rheometry successfully quantify the viscoelastic response of polyvinyl alcohol (PVA) solutions and identify formulations changes such as additive addition. The flow behavior of PVA solutions was correlated to dissolution behavior proving that the developed protocol has a high potential as a first screening tool.