Polystyrene (PS) fiber mats incorporating iron (Fe) particles were fabricated by electrospinning and the hydrophobicity of the resulting magnetic fabrics was investigated with and without an applied magnetic field. The results show that the hydrophobicity (as measured using water droplet contact angle) increases in the presence of a magnetic field and the hysterisis in the advancing/receding contact angle (a measure of the stickiness of the surface) decreases in the presence of a magnetic field. It is also shown that the contact angle and hysterises increase with decreasing fiber diameter and mat thickness.

Master of Science / Department of Apparel, Textiles, and Interior Design / Jooyoun Kim / Seong-O Choi / Superhydrophobicity (water contact angle, WCA >150˚) can be achieved by introducing surface roughness and decreasing surface energy. Polystyrene (PS) electrospun web can be used as an excellent substrate for superhydrophobic surface due to its low surface energy (~33 mN/m) and processibility to form various roughness. As the Cassie-Baxter model explains, the presence of roughness amplifies anti-wettability of materials whose surface energy is low (hydrophobic, WCA >90˚). This study aims to fabricate superhydrophobic PS nonwoven webs by electrospinning process and vapor deposition of 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFDTS) and to investigate the influence of fiber morphology and surface energy on wettability. To this end, PS webs with various fiber morphologies were electrospun under different polymer concentrations and solvent mixtures. PS substrates were treated by air plasma to attach –OH groups before the vapor deposition of PFDTS. Air plasma treatment itself increased the surface energy of PS; however, with PFDTS coating, the surface energy was decreased. The wettability was characterized by WCA and sliding angle measurement. WCAs on the electrospun webs were greater than that of flat PS film (WCA=95˚) due to the increased roughness of the web. The web with beads or grooved fibers achieved superhydrophobicity (WCA>150˚). PFDTS deposition lowered the surface energy of PS surface to about 15.8 mN/m. PS web with PFDTS deposition presented high water contact angle up to 169˚ and low sliding angle about 3˚. Also it was attempted to characterize the interfacial area between water and a solid surface on irregular fibrous webs. The fraction of solid surface area wet by the liquid (solid fraction) was observed by staining the rough electrospun web with a hydrophobic fluorescent dye, coumarin. The actual solid fraction corresponded fairly well with the theoretical solid fraction calculated by the Cassie-Baxter equation, demonstrating that the treated superhydrophobic surface follows the Cassie-Baxter wetting state.

Através da aplicação de microusinagem com laser de femtossegundos é possível fazer ablação de cavidades com precisão de poucos μm. Se comparado com o processo de litografia, por exemplo, apresenta algumas vantagens como poder ser aplicada em praticamente qualquer tipo de substrato e utilizar tecnologia simples de usinagem assistida por computador para a geração de perfis de duas ou três dimensões. O objetivo deste trabalho foi estudar estratégias e parâmetros com laser de femtossegundos para ablação dos polímeros poliestireno e polidimetilsiloxano (PDMS), de forma a afetar o mínimo possível as características das regiões adjacentes à usinagem. Como exemplos de aplicações, temos o primeiro material que tem sido texturizado para cultura controlada de células do coração e o segundo que faz parte da estrutura de certos circuitos microfluídicos. A fim de se fazer um levantamento dos limiares de ablação destes materiais, foram utilizadas as técnicas D-Scan e regressão de diâmetro. Diversos traços foram realizados variando-se as velocidades de deslocamento da amostra. Com isso, foram analisados os efeitos de incubação e a relação da sobreposição de pulsos com a largura dos traços criados. Por fim foram incluídos incrementos laterais entre os traços, obtendo-se uma área ablacionada. Procurou-se variar a frequência dos pulsos nos experimentos para investigar o aparecimento de um possível efeito térmico com diferentes intervalos de tempo entre pulsos consecutivos. Foram conseguidos parâmetros em que é possível realizar a ablação de pontos, traços e superfícies sem aparente fusão do material. Porém observou-se que o aspecto do perfil ablacionado não tem a tendência de ficar liso e uniforme. Os resultados demonstram a enorme variedade de combinações e parâmetros que podem ser obtidos com a técnica de microusinagem com laser de femtossegundos e favorecem o estudo do processamento destes polímeros. / Through the use of femtosecond laser micromachining, it is possible to ablate cavities with accuracy in the order of a few micrometers. Compared with lithography process, for example, it has some advantages such as being able to be applied to virtually any type of substrate and using simple computer assisted machining technology for the generation of two or three dimensional profiles. The objective of this work was to study strategies and parameters with femtosecond lasers for the ablation of polystyrene and PDMS polymers, in order to affect, as little as possible, the characteristics of these materials. As examples of applications, the first material has been textured for controlled culture of heart cells and the second is used in microfluidic circuits. In order to find out the ablation thresholds of these materials, the D-Scan technique and diameter regression were used. Several traces were performed by varying the sample displacement velocities. Thus, the effects of incubation and the relation of the overlapping of pulses with the width of the traces created were analyzed. Finally, lateral increments were included between the traces, obtaining an ablated area. It was attempted to vary the pulse frequency in the experiments to investigate the appearance of a possible thermal effect with different time intervals between consecutive pulses. Parameters were obtained in which it is possible to perform the ablation of points, traces and surfaces without apparent melting of the material. However, it has been observed that the aspect of the ablated profile does not tend to be smooth and uniform. The results demonstrate the enormous variety of combinations and parameters that can be obtained with the femtosecond laser micromachining technique and favor the study of the processing of these polymers.

A polimerização em emulsão de estireno em um microrreator Syrris de 250 µL com misturador estático junção \"T\" foi estudada em duas etapas. Primeiro somente a fluidodinâmica deste dispositivo não convencional foi avaliada, depois, foi desenvolvida a reação de polimerização de forma a observar como este fator influencia no sistema. Os experimentos foram realizados procurando se atingir maiores conversões, mas mantendo a estabilidade da emulsão. Foi um trabalho exploratório, portanto se assemelha mais a um processo de evolução (evolutionary process). Foram verificados a partir de qual relação das vazões dos dois fluidos ocorre a formação de gotas, e que com o aumento da vazão da fase contínua, aquosa (Qc), mantendo constante a vazão da fase dispersa (Qd), foi verificado uma diminuição do diâmetro das gotas e um regime de fluxo laminar. Posteriormente, realizou-se a polimerização em emulsão do estireno no microrreator, porém com restrições para altas vazões. Os parâmetros de processo testados foram a proporção Qc e Qd, a temperatura e a concentração do iniciador para então verificar o efeito que a variação destas ocasionam na conversão de monômero, no diâmetro e número de partículas e nas massas moleculares médias. A polimerização foi feita para soma das vazões Qc e Qd da ordem de 100 µ L/min, com 15% de monômero na formulação e com o maior tempo de residência possível de 2,5 minutos. Para maiores concentrações de monômero, acima de 15% foi verificado entupimento do canal do microrreator. A taxa de conversão de monômero aumentou com o aumento da temperatura e com o aumento da concentração do iniciador, mas o maior valor atingido foi de apenas 37% devido ao baixo tempo de residência. Nos casos de maiores taxas de conversão, as massas moleculares obtidas foram as menores conforme o esperado pela teoria. Finalmente, os índices de polidispersão (PDI), obtidos foram da ordem de 2,5 a 3,5. / The emulsion polymerization of styrene in a microreactor Syrris 250 µL with static mixer junction \"T\" was studied in two steps. First, only the fluidynamics of this nonconventional device was evaluated, after the polymerization reaction was developed in order to observe how this factor influencing the system. The experiments were performed seeking to achieve higher conversions, keeping the stability of the emulsion. It was an exploratory work therefore is more like an evolutionary process. The ratio of two-phase flow rates was analyzed from which of them occurs droplet formation. The flow rate of dispersed phase (Qd) was kept constant and the continuous phase (Qc), was increased. It can be observed the decreasing of droplet diameter and a laminar flow regime. Later, it was carried out emulsion polymerization of styrene in the microreactor with restrictions for high flow rates. The process parameters were analyzed: the ratio Qc/Qd, the temperature and initiator concentration and then determine the effect that these variations cause the monomer conversion, the diameter, number of particles and the average molecular weight. The polymerization occurred to the sum of the flow rates Qc and Qd of around 100 µ L/min with 15% monomer in the formulation with the highest residence time of 2,5 minutes. For higher concentrations of monomer, above 15% was observed clogging in the microreactor channel. The monomer conversion rate raised with increasing temperature and with the concentration of initiator, but the largest value achieved was only 37% due to the low residence time. In this case, the molecular weights obtained were smaller as expected by theory. Finally, the polydispersity indexes obtained were around 2.5 to 3.5.

Ionômeros são polímeros carregados que possuem uma variedade de propriedades elétricas e que recentemente vêm sendo aplicados como camadas de transporte em dispositivos poliméricos. Em particular, camadas ultrafinas de ionômeros são depositadas entre o eletrodo e o polímero eletrônico em OLEDs para aumentar a eficiência da injeção de cargas. Entretanto o sucesso desta aplicação envolve fenômenos de armazenamento e mecanismos de transportes de cargas dentro do ionômero que ainda não são claramente entendidos. Neste trabalho foi utilizada a técnica da corrente despolarização termoestimulada (TSDC) com o propósito de esclarecer alguns efeitos relacionados a esse fenômeno. Nós utilizamos o poliestireno sulfonado (X-SPS) com lítio (X = Li) ou potássio (X = K) como contraíon. Foram obtidos filmes ultrafinos com 50 nm de espessura por spincoating obtendo a estrutura metal-polímero-metal para estudo, tendo como metal o alumínio. A técnica de TSDC consiste no aquecimento de uma amostra previamente polarizada a um taxa de aquecimento constante e a corrente de despolarização é medida em função da temperatura da amostra. Os resultados experimentais mostraram que cada termograma apresenta dois picos, sendo que um dos deles mostrou-se fortemente dependente das condições de polarização, ou seja, dependendo da temperatura de polarização e da intensidade do campo de polarização. Os picos foram estudados através da cinética de primeira ordem para a dinâmica de armazenamento e transporte, e dos ajustes teórico-experimental foram obtidos importantes parâmetros, tal como, a energia de ativação e concentração de espécies ativas. / Ionomers are charged polymers that exhibit a great variety of electrical properties and more recently they have been applied as transport layers at polymer devices. In particular, thin films of ionomer have been deposited between the electrodes and the electronic polymers in OLEDs to improve the efficiency of the charge injection. Despite the success of such application, the involved phenomena related to the charge storage and transport mechanisms inside the ionomer thin layer are not clear yet. In this work we used thermal stimulated depolarization current technique (TSDC) with the purpose to elucidate such phenomena. We used for this a sulfonated polystyrene (X-SPS) having lithium (X = Li) or potassium (X = K) as cation counter-ions, and we make structure of metal-polymer-metal in which the polymer is a thin film of SPS, at about 50 nm thick and deposited by spincoating, having aluminum as metal. TSDC technique consists of warm up a previously polarized sample at a constant rate of heating and measure the depolarization current in function of the temperature. The experimental results showed that each thermogram presents two peaks, one of them very dependent on the polarization conditions, i. e., it depends on the polarization temperature and the intensity of the polarization bias. The peaks were studied by considering first order trapping-detrapping (or dipole relaxation) kinetics, from which important parameters, as the activation energy, were obtained.

Foi estudada a cristalização de suspensões aquosas de esferas de poliestireno (850&#197, 910&#197 e 1090&#197 de diâmetro) no limite de baixas concentrações -1011 a 1013 esferas / cm3. A dependência do parâmetro de rede com a concentração original (n) da suspensão aquosa apresenta uma transição de fase da fase bcc para fcc, conforme já foi observada por outros autores. Observamos também que durante a cristalização a concentração de esferas no cristal Ra sistematicamente maior do que na solução original, portanto a água estaria sendo expelida para a solução durante a cristalização. Baseado nestas observações nós propomos um modelo de cristalização onde os cristalites (concentração n1) estão em equilíbrio termodinâmico com uma solução com concentração n2 (n1&#62 n &#62 n2), dando para cada concentração inicial um diferente parâmetro de rede determinado por este equilíbrio. Nossos resultados mostraram que o coeficiente de expulsão da água durante a cristalização é dependente do raio da esfera. Para realizar as medidas de parâmetro de rede nós adaptamos para as nossas condições particulares o método de Debye-Scherrer usado em difração de raios-X por cristais. O equivalente à fonte de raios-X era um laser de Argônio com comprimentos de onda variáveis. Diversas experiências novas são sugeridas. / The crystallization of aqueous suspensions of polystyrene spheres 850&#197, 910&#197 and 1090&#197 of diameter) was studied in the limit of low concentration -1011 to 1013 spheres / cm3. The dependence of the lattice parameter with the original concentration (n) of the aqueous suspension shows a phase transition from bcc to fcc phase as it was already been observed by others authors. We also observed that during crystallization the concentration of spheres in the crystal was systematically higher than in the original solution, showing that water should be expelled toward the solution during crystallization where the crystallites (concentration n1) are in thermodynamic equilibrium with a solution with concentration n2 (n1&#62 n &#62 n2) giving for each initial concentration a different lattice parameter determined by this equilibrium. Our results showed that coefficient of water rejection during crystallization is dependent on the sphere radius. In order to make the measurements of the lattice parameter we adapted to our particular conditions the Debye-Scherrer method used in X-ray diffraction of crystals. The equivalent to the X-ray source was a tunable Argon laser. Several new experiments are suggested.

Neste trabalho foram investigados a obtenção de argilas organofílicas e nanocompósitos de Poliestireno com estas argilas. A primeira parte deste trabalho teve como objetivo a modificação de argilas esmectíticas naturais brasileiras, tornando-as organofílicas e adequadas à aplicação em nanocompósitos de matriz poliméricas. Para modificação foram utilizados sais quaternários e foi avaliado quais parâmetros do processo de obtenção mais influenciam nas propriedades das argilas organofílicas. Para tanto foi utilizada a argila Brasgel (fornecida pela BUN, e naturalmente cálcica), e foram propostos diferentes métodos de preparo de argilas, onde quatro parâmetros foram avaliados: os sais quaternários amônio; a granulometria da argila (#400 e coloidal), a temperatura de processamento (ambiente e a 70oC) e os tempos utilizados durante o processo de incorporação dos sais quaternários na estrutura dos materiais argilosos. Os materiais obtidos foram caracterizados por difração de raios-X (DRX), ensaios de inchamento de Foster e analise térmica diferencial (DTA). Obteve-se incremento do espaçamento basal com todas as argilas utilizadas. Mostrou-se que os dois principais parâmetros determinantes na incorporação das argilas são o tempo de mistura e a temperatura (de 70oC) empregada. A segunda parte do trabalho teve como objetivo obter nanocompósitos de PS com argilas organofílicas (sendo uma argila obtida na primeira parte e uma comercial, Cloisite 20A) via intercalação no polímero fundido. Os nanocompósitos foram preparados em extrusora de rosca dupla e em misturador interno. As argilas foram adicionadas ao polímero fundido na forma de um pó e em suspensão de etanol. Os nanocompósitos obtidos foram moldados por compressão e injeção (com variações nas condições de injeção para avaliar a influencia na estrutura final), para realização da caracterização. A principal técnica de caracterização utilizada foi a caracterização reológica com ensaios de cisalhamento de pequenas amplitudes (COPA) e de varredura de tempo. Os materiais foram caracterizados também por técnicas auxiliares como DRX, microscopia eletrônica de transmissão (MET), analises térmicas diferenciais (DTA) e ensaios mecânicos. Obteve-se nanocompósitos de estrutura intercalada. Os materiais obtidos no misturadores mostraram as melhores dispersões de argila. . Verificou-se que o tempo de residência dos materiais é um dos fatores mais importantes na obtenção dos nanocompósitos. Os ensaios mecânicos não mostraram alteração significativa. / In this work, the obtention of organoclays and nanocomposites of polystyrene (PS) using these modified clays was studied. In a first part Brazilian smectites clays were modified to be used in clay containing polymer nanocomposites. Several quaternary ammonium salts and experimental methods to modify the clays were used. In particular four parameters were evaluated: the type of ammonium salt, the particle clay size, the temperature and time used during the process of modification. The samples obtained were characterized by X-ray diffraction (XRD), Foster swelling test and differential thermal analysis (DTG). The results indicated that the most two important parameters in the process of modification are the time and the temperature used. In a second part nanocomposites of PS with organoclays (one obtained in the first part, and commercial clay, named cloisite 20A) were obtained by melt intercalation method using a twin screw extruder and an internal mixer. The clays were incorporated to the polymer as a fine dried powder and as a suspension of ethanol. Nanocomposites were molded by compression and injection. The injection conditions were modified to evaluate their influence on the morphology of the samples. The nanocomposites samples were characterized by XRD, transmission electronic microscopy (TEM), DTG and mechanical tests. Small amplitude oscillatory shear (SAOS) and time sweep tests were carried out. Nanocomposites of intercalated structure were obtained. The ones obtained using the internal mixer were shown to present a finer microstructure. The experimental results revealed that the residence time was showed the most important parameter in obtention of nanocomposites.

Waste plastic treatment was a global issue currently. A sustainable recycling process was required to recovery the monomer units from the polymer, thus avoiding environmental impacts due to disposal and enhancing the economic benefit from the recovered products. Pyrolysis was one of the promising process and previous MQP group has studied the pyrolysis with molten salts. In this work, a standardized and optimized pyrolysis reaction process of polystyrene was developed, based on the previous work on molten salt pyrolysis 5. The literature of pyrolysis mechanism and catalytic effects were reviewed as a guide process design. The orientation of the reactor was standardized to be consistent with literature record of preceding work. The positioning of the flow tube for the carrier gas and thermocouple were standardized in locations to provide mixing process of the reactant, the removal of products, and the accurate measurement of reaction temperature. The product collection system was also investigated and optimized to maximize collection efficiency while avoiding excessively low temperatures. The experiment results with standardized reaction configuration showed an improved styrene yield, 65%, compared with a previous yield of 44%. Then with the standardized reaction configuration, the catalytic effects of molten salt were studied at 400℃ pyrolysis temperature. Quantitative analysis indicated that the molten salt improved the styrene selectivity of the monomer compared to the dimer. Analysis of product composition and mass balance indicated formation of heavy non-GC detectable species in the liquid products. Gas phase secondary reaction during pyrolysis, and re-polymerization inside the liquid products, were discussed to explain the different styrene yield and the existence of heavy species. Based on the current results, recommendations for the pyrolysis temperature, initial reactants loading, and condenser temperature and analysis strategies were provided for further study of the molten salt pyrolysis of polystyrene.

Zhou, Wenjia = 聚苯乙烯/銀聚合物納米棒陣列的合成、表征與生長的研究 / 周文佳. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 69-73). / Text in English; abstracts in English and Chinese. / Zhou, Wenjia = Ju ben yi xi / yin ju he wu na mi bang zhen lie de he cheng, biao zheng yu sheng zhang de yan jiu / Zhou Wenjia. / Chapter I. --- Abstract / Chapter IV. --- Acknowledgement / Chapter V. --- Contents / Chapter 1 --- Introduction / Chapter 1.1 --- Motivations / Chapter 1.2 --- Overview of the thesis / Chapter 2 --- Instruments / Chapter 2.1 --- Introduction to electron microscopes / Chapter 2.2 --- Scanning electron microscope / Chapter 2.2.1 --- Introduction to SEM working principle / Chapter 2.2.2 --- Electron specimen interactions and their applications in SEM / Chapter 2.2.3 --- Specific SEM conditions in the experiments / Chapter 2.3 --- Transmission electron microscope / Chapter 2.3.1 --- Introduction to TEM working principle / Chapter 2.3.2 --- Imaging mode and diffraction mode in TEM / Chapter 2.3.3 --- X-ray microanalysis with TEM / Chapter 2.3.4 --- Specific TEM conditions in the experiments / Chapter 3 --- Anodic aluminum oxide templates with different parameters / Chapter 3.1 --- Introduction to self-ordered anodic aluminum oxide / Chapter 3.1.1 --- Electrochemistry of anodic alumina / Chapter 3.1.2 --- Pore growth mechanism / Chapter 3.1.3 --- Self-ordered alumina by two-step anodization / Chapter 3.1.4 --- Other advanced methods for fabrication of monodomain AAO / Chapter 3.1.5 --- Applications of AAO templates in nanomaterials fabrication / Chapter 3.2 --- Preparation procedures of porous AAO templates we used / Chapter 3.2.1 --- Experimental setup / Chapter 3.2.2 --- General preparation procedures of AAO thin film on Al / Chapter 3.3 --- Experimental data of AAO templates with different parameters / Chapter 3.3.1 --- Different interpore distances / Chapter 3.3.2 --- Different pore depths and pore sizes / Chapter 3.3.3 --- Calibration of AAO templates pore depths and pore sizes at different anodic potentials / Chapter 4 --- Preparation of free standing polystyrene nanorods arrays with different parameters / Chapter 4.1 --- General preparation procedures of free standing polymer nanorods arrays / Chapter 4.2 --- Different rods intervals and diameters / Chapter 4.3 --- Limitations to the rods lengths control / Chapter 4.4 --- Discussion on the polymer properties for the successful preparation of free standing polymer rods arrays / Chapter 5 --- Thermal reduction method to embed Ag nanoparticles inside the polymer rods / Chapter 5.1 --- General preparation procedures of PS/Ag nanorods arrays / Chapter 5.2 --- Analysis method and procedure of Ag nanoparticles inside PS rods / Chapter 5.3 --- Typical TEM images of the three series samples / Chapter 5.4 --- Data analysis of Ag nanoparticles inside PS rods / Chapter 5.5 --- Discussion on Ag particles growth process / Chapter 5.6 --- Conclusion and suggestions for improvement / Chapter 6 --- Conclusion / Reference / Appendix

Polymers of various types are added to crude oils and oil products to prevent wax deposition, break water-in-oil emulsions, reduce drag in pipelines and to stabilize asphaltenes. In mixtures where a polymer does not adsorb on colloids, two stable liquid phases can arise due to depletion flocculation. Asphaltenes in heavy oils and toluene mixtures form sterically stabilized colloidal particles. In this work, the addition of a non-adsorbing polymer (polystyrene) to C5 Maya asphaltene + toluene mixtures was investigated experimentally and theoretically. As concentrated asphaltene + toluene mixtures are opaque to visible light, phase volumes and compositions were detected using ultrasound. The sensors comprised two commercial 64 element phased-array acoustic probes. The operation of the view cell, and kinetic and equilibrium data processing procedures were validated using mixtures of methanol + alkanes. Acoustic speed and attenuation profiles were found to provide independent measures of phase separation. At equilibrium, acoustic speed profiles are uniform in each phase with a step change at the interface. Acoustic wave attenuation profiles exhibit a sharp peak/spike at liquid-liquid interfaces. Mixtures of asphaltenes + polystyrene + toluene are shown to exhibit liquid-liquid phase behavior over broad ranges of composition. This is the first report of liquid-liquid phase behavior for such mixtures. One phase is asphaltene rich and the other phase is polystyrene rich. Liquid-liquid critical points were also identified along the liquid-liquid/liquid phase boundary for mixtures with two mean molar masses of polystyrene. Compositions of co-existing phases were computed using phase volume variations along dilution lines, acoustic speed data and a mass balance model. A parameter was introduced to improve the agreement between calculated and experimental speeds of sound. The results of the model indicate that more than half of the asphaltenes, by volume, participate in the depletion flocculation process. Phase compositions were measured independently using UV-visible spectrophotometry. The nominal size of asphaltene colloidal particles participating in the phase separation mechanism was estimated by comparing calculated phase boundaries with the experimental phase diagram. The estimated size of asphaltene colloidal particles is in agreement with the expected size of asphaltenes in toluene mixtures obtained exogenously. / Chemical and Materials Engineering