Thesis (PhD (Physics))--University of Stellenbosch, 2006. / This thesis is devoted to a study of the 93Nb( p r ,3He) and 59Co( p r ,3He) reactions at incident energies of 100 MeV, 130 MeV and 160 MeV. Double differential cross sections and analysing power distributions were measured from a threshold of ~30 MeV up to the kinematic maximum and at scattering angles between 15º and 120º. The experimental data were compared with theoretical calculations done by combining a statistical multistep theory with a deuteron pickup mechanism in the final stage. The contribution of the first three steps towards the total double differential cross section and analysing power was assessed. The theory described the experimental double differential cross section and analysing power data reasonably well over all incident and scattered energies and for both target nuclei. As the incident energy was increased, the characteristics of the reaction mechanism also remained consistent. Thus the results supported the underlying multistep-pickup theory. The two target nuclei demonstrated similar responses, suggesting these two share the same basic reaction mechanism. The total double differential cross section for the reaction dropped with an increase in incident energy. At a fixed emission energy, near the maximum allowed value, the slope of the double differential cross section increased with an increase in incident energy, resulting in the dominance of forward peaked reactions at higher incident energies. The sensitivity of analysing power to the multistep part of the reaction was valuable to the study. Forward-peaked contributions that were associated with single step direct reactions resulted in large analysing power values at small scattering angles, and values dropped to around zero at large angles. The analysing power also appeared to decrease to values approximating zero as the incident energy was increased to 160 MeV. Furthermore, this study also confirmed the dominance of higher step mechanisms at high excitation energies, irrespective of incident energy. In general the results were in agreement with the predicted properties of the assumed reaction mechanism at all incident and emission energies, which inspires confidence that the theoretical interpretation is likely to be correct.

TiB2 particle reinforced aluminum matrix composites have been the subject of several investigations. An M.Sc. thesis on production of TiB2 reinforced aluminum composites by reaction between liquid aluminum and B2O3 and TiO2 dissolved in cryolite has been completed in this Department in 2005. This study is a continuation of the mentioned M.Sc.study. Composition of the starting cryolite-B2O3-TiO2 system, temperature and time were used as experimental variables. The resulting composite was squeeze cast and its microstructure was examined. Mechanical properties of the produced composite were measured and how mechanical properties of the composite vary with TiB2 content of the composite was determined.

In this study, production and properties of titanium diboride particle reinforced aluminum matrix composite were investigated. TiB2 particles form in-situ through the reaction of TiO2 and H3BO3 and Na3AlF6 in aluminum melt. The results showed that the in-situ TiB2 particles formed were spherical in shape and had an average diameter of 1mm .Moreover, the distribution of TiB2 particles in the matrix were uniform. The ultimate tensile strength, yield strength, flexural stress and hardness were found to while reduction in area and elongation were found to decrease with increase in reinforcement content in the matrix.

Made available in DSpace on 2015-04-01T12:17:41Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3689736 bytes, checksum: 727f212a3d43cfe51e158ce0f1485daf (MD5) Previous issue date: 2013-07-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In last years there has been a huge concern about environment. This present study aims to study the viability of using mollusk shell powder, as particulate reinforcement in polymer composites of High Density Polyethylene (HDPE), in order to this research contributes potentially to mitigate the environmental impact caused by increase of shell waste associated with mollusk commercial activities on the coast of Paraiba State. To this end, a study on influence of mollusk shell additions (for concentrations of 2, 5 and 8% in weight and for granulometries with both 200 and 325 meshes) in changing the mechanical, morphological, and thermal properties of pure HDPE is done. In addition, a titanate coupling agent was used to treat surfaces of mollusk shell powder of the composite having 5% in weight of shell. All composites were processed in a single-screw extruder with a mixing component (Madock) and specimens are molded by injection. It was performed a chemical characterization of the shell powder by X-ray fluorescence in order to identify its constituents and it was found 97.95% calcium oxide, which is the main constituent of calcium carbonate. In addition, it was performed a MFI analysis and thermal, morphological, and mechanical characterization for all composites as well as for pure HDPE. The MFI analysis of the composites showed only slight changed, therefore the mollusk shell did not influence definitely on rheological behavior of the pure HDPE.The cristalinity degree of the pure UHWPE increased when mollusk shell powder was increased. The composition of 5% in weight with granulometry of 325 mesh produced the highest increase of cristalinity degree of non-treated powders, almost 29%, whereas 38% cristalinity degree was obtained when a 200-mesh composition of 5% in weight was treated with the titanate coupling agent. This behavior suggest a probable effect of particles as nucleating agent. Fracture surfaces show there is both low bonding among the phases and particle agglomerates, mainly in 8% composite for both granulometries. The addition of shell powder changed tensile mechanical properties of pure HDPE, where in major cases its stiffness was increased excepted for 5% compositions. Both the impact strength and bending mechanical properties of the pure HDPE were increased when the thinner shell powders were additioned. Hence shell powder is a potential particle reinforcement for use in HDPE composites. / Nos últimos anos existe uma preocupação muito grande com meio ambiente. O presente estudo tem como objetivo estudar a viabilidade do uso de pó de conchas de moluscos, como carga particulada em compósitos poliméricos de polietileno de alta densidade, (PEAD) a fim de que essa pesquisa contribua potencialmente para amenizar o impacto ambiental causado pelo aumento da produção dessas conchas, associadas com as atividades comerciais de moluscos, ao longo de toda a costa do estado da Paraíba. Com este objetivo foi realizado um estudo sobre a influência da concha, nas concentrações de 2, 5, 8% em massa, nas granulometrias de 200 e 325 mesh, sobre as propriedades mecânicas, morfológica e térmica do PEAD puro. Neste estudo, um agente de acoplamento titanato também foi utilizado para tratar as superfícies das partículas do pó da concha do compósito contendo uma concentração de 5 % de concha. Os compósitos foram processados em uma extrusora mono rosca com um componente de mistura(Madock) e os corpos de prova foram moldados por injeção. Foi realizado uma caracterização química no pó da concha por fluorescência de Raio X para verificar seus constituintes, e encontrando 97,95% de oxido de cálcio constituinte principal do carbonato de cálcio. Também foi realizada análise de MFI, caracterização térmica, morfológica e mecânica para todos os compósitos e para o PEAD puro. O MFI dos compósitos teve pequena alteração, logo a carga não influenciou o comportamento reológico do PEAD. O grau de cristalinidade do PEAD puro aumentou à medida que o teor de pó de concha foi aumentado, sendo que a composição de 5% em massa, na granulometria de 325 mesh foi a que apresentou maior aumento, quase 29% com relação ao puro, já o compósito com 5% em massa de pó de concha(200 mesh) tratado com agente de acoplamento titanato teve um aumento de quase 38%. Esse comportamento indica um provável efeito nucleante dessas partículas. A superfície de Fratura mostrou que existe pouca adesão entre as fases presentes e que existem aglomerados das partículas, principalmente com a composição de 8% nas duas granulometrias. A adição da concha alterou as propriedades mecânicas sob tração do PEAD puro, de um modo geral, sua rigidez foi aumentada, exceto os compósitos contendo 5% em massa, que diminuíram o módulo de elasticidade do PEAD puro. A resistência ao impacto e as propriedades mecânicas sob flexão do PEAD puro foram aumentadas com a adição do pó de concha, com a granulometria mais fina. O pó da concha é um reforço particulado potencial para o uso em compósitos de PEAD.

This research is focused on preparation of polypyrrole (PPy) composite particles by using socalled template oxidative polymerization method. As a template, water-soluble polymers, polymeric microgels, latex particles or bulk gels can be used. The morphology and properties of the composite particles can be controlled effectively by the proper use of the template. By choosing the dopant anion or oxidation agent it is possible to vary the conductivity of the polymer. In the case when uncrosslinked PVME was used as stabilizer, core-type polypyrrole spherical particles in the range of 50-100 nm were formed in both aqueous ethanol and water. Results of the elementary analysis, IR spectroscopy confirmed that the anionic salts can be incorporated in the PPy particles and play as the dopants. The presence of dopants in polypyrrole enhances the conductivity, especially in the case of sodium benzoate the conductivity of the final product has been improved by 3 orders. Polymeric microgels were also applied as the templates for polypyrrole deposition. When crosslinked PVME microgels were used in the oxidation polymerization of pyrrole, large PPy fibrils (appr. 400nm) were formed. Needle-like particles were formed due to the porous structure of microgels, which play a template role in the pyrrole polymerization process. When poly(VCL/AAEM) microgels were used as a template for oxidative polymerization of pyrrole, "raspberry-like" composite particles will be formed with PPy domains located in swollen hydropholic particle shell. Obtained stable composite microgels show similar thermal sensitivity as poly(VCL/AAEM) particles with fully reversible collapse-swelling properties. Increase of PPy content in composite particles increases conductivity of the composite material. The conductivity of composite particles prepared in water was much higher than that of prepared in water : ethanol mixtures. Furthermore, monodisperse PS-PEGMA particles, which were prepared in water medium by polymerization with sodium peroxydisulfate have been used as a template for deposition of polypyrrole (PPy). Obtained composite particles possess core-shell morphology where shell is composed out of small PPy nano-domains. The shell thickness can be varied by changing PPy load, controlling the overall template surface area in the system, and by influencing the pyrrole polymerization kinetics in presence of different oxidants. The last possibility provides also incorporation of different anions into polypyrrole shell. The stability of composite particles decreases gradually if the deposited PPy amount increases. It has been established that obtained particles are intrinsically coloured and the colour can be changed by the PS-PEGMA core size. Conductivity measurement shows that PS/PEGMA/PPy composite particles prepared by using phosphomolybdate as the oxidant are much more conductive than the particles prepared by the other two oxidants. The conductivity increases with the increase of PPy load in the system. Overall, the proper design of the template should give a possibility to control effectively the morphology, particle size and provide sufficient stability to the composite particles. Different morphologies, such as spherical, core-shell, raspberry and needle-like, with different particle size are expected to be available in different cases. By choosing the dopant anion or oxidation agent it is possible to vary the conductivity of the polymer. The stable water-based dispersions are expected to be used as additives for paint formulations, in electrorheology, microelectronic, ion-separation or disease diagnostics.

The Electrospray (ES) technique is a promising particle generation method for drug delivery due to its capabilities of producing monodisperse PLGA composite particles with unique configurations and high drug encapsulation efficiency. In the dissertation work, the coaxial dual capillary ES was used to generate drug-loaded core-shell PLGA particles to study the effects of particle filling materials, drug loading locations and particle shell thicknesses on the resultant in vitro release behaviors of the hydrophilic and/ or hydrophobic model drugs. Through release profile characterization of drug-loaded PLGA particles (particle size: 400 nm and 1 μm), it was confirmed that the co-encapsulation of Budesonide (BUD, the hydrophobic small-molecule model drug) and Theophylline (THY, the hydrophilic small-molecule model drug) in the particle cores is the most effective drug loading strategy for extended release of the fixed combined BUD and THY. Particles composed of PLGA fillers with lower molecular weights and with greater shell layer thicknesses could release THY in a well controlled fashion. On the other hand, a slower release rate of Bovine Serum Albumin (BSA, the protein model drug) from PLGA particles with greater shell thickness was also observed. Sequential release of BSA and Paclitaxel (PTX, the hydrophobic small-molecule anti-cancer model drug) was achieved by the 400-nm PLGA (Mw: 7,000-17,000 g/mol, LA/GA: 50/50) particles with potential biopharmaceutical applications in cancer therapy.

Metallic nanoparticles are unique materials for optical, electronic, catalytic, and sensing applications. Due to the vast flexibility in controlling the surface chemistry of these particles through functionalization there is a great deal of interest in using metallic nanoparticles as building blocks in the development of more complex nanostructures through the use of a 'bottom-up' approach. Using self assembly techniques, one can exploit spontaneous chemical interactions to build complex constructs on the nanometer scale. Towards this end, gold nanorods have been synthesized and modified with various polymers, inorganic oxides and organic ligands to establish principles for self-assembly of these unique nanomaterials. Gold nanorods are of great interest due to their strong optical absorption in the visible and near infrared regions, which can be tuned through material preparation and modification of the surrounding environment. This thesis focuses on investigating approaches for both irreversible and reversible self-assembly of gold nanorods. Techniques such as dynamic light scattering (DLS), ultraviolet-visible (UV) spectroscopy, transmission electron microscopy (TEM), and polarization modulation infrared reflection absorbance spectroscopy (PM-IRRAS) were used to characterize the colloidal particles and gold surfaces. A novel contribution of this work is the successful demonstration of end-to-end linking of gold nanorods in a rapid and reversible manner using a pH responsive polypeptide.

abstract: Polymer-gold composite particles are of tremendous research interests. Contributed by their unique structures, these particles demonstrate superior properties for optical, catalytic and electrical applications. Moreover, the incorporation of “smart” polymers into polymer-gold composite particles enables the composite particles synergistically respond to environment-stimuli like temperature, pH and light with promising applications in multiple areas. A novel Pickering emulsion polymerization route is found for synthesis of core-shell structured polymer-gold composite particles. It is found that the surface coverage of gold nanoparticles (AuNP) on a polystyrene core is influenced by gold nanoparticle concentration and hydrophobicity. More importantly, the absorption wavelength of polystyrene-gold composite particles is tunable by adjusting AuNP interparticle distance. Further, core-shell structured polystyrene-gold composite particles demonstrate excellent catalyst recyclability. Asymmetric polystyrene-gold composite particles are successfully synthesized via seeded emulsion polymerization, where AuNPs serve as seeds, allowing the growth of styrene monomers/oligomers on them. These particles also demonstrate excellent catalyst recyclability. Further, monomers of “smart” polymers, poly (N-isopropylacrylamide) (PNIPAm), are successfully copolymerized into asymmetric composite particles, enabling these particles’ thermo-responsiveness with significant size variation around lower critical solution temperature (LCST) of 31°C. The significant size variation gives rise to switchable scattering intensity property, demonstrating potential applications in intensity-based optical sensing. Multipetal and dumbbell structured gold-polystyrene composite particles are also successfully synthesized via seeded emulsion polymerization. It is intriguing to observe that by controlling reaction time and AuNP size, tetrapetal-structured, tripetal-structured and dumbbell-structured gold-polystyrene are obtained. Further, “smart” PNIPAm polymers are successfully copolymerized into dumbbell-shaped particles, showing significant size variation around LCST. Self-modulated catalytic activity around LCST is achieved for these particles. It is hypothesized that above LCST, the significant shrinkage of particles limits diffusion of reaction molecules to the surface of AuNPs, giving a reduced catalytic activity. Finally, carbon black (CB) particles are successfully employed for synthesis of core- shell PNIPAm/polystyrene-CB particles. The thermo-responsive absorption characteristics of PNIPAm/polystyrene-CB particles enable them potentially suitable to serve as “smart” nanofluids with self-controlled temperature. Compared to AuNPs, CB particles provide desirable performance here, because they show no plasmon resonance in visible wavelength range, whereas AuNPs’ absorption in the visible wavelength range is undesirable. / Dissertation/Thesis / Doctoral Dissertation Chemical Engineering 2015

This research is focused on preparation of polypyrrole (PPy) composite particles by using socalled template oxidative polymerization method. As a template, water-soluble polymers, polymeric microgels, latex particles or bulk gels can be used. The morphology and properties of the composite particles can be controlled effectively by the proper use of the template. By choosing the dopant anion or oxidation agent it is possible to vary the conductivity of the polymer. In the case when uncrosslinked PVME was used as stabilizer, core-type polypyrrole spherical particles in the range of 50-100 nm were formed in both aqueous ethanol and water. Results of the elementary analysis, IR spectroscopy confirmed that the anionic salts can be incorporated in the PPy particles and play as the dopants. The presence of dopants in polypyrrole enhances the conductivity, especially in the case of sodium benzoate the conductivity of the final product has been improved by 3 orders. Polymeric microgels were also applied as the templates for polypyrrole deposition. When crosslinked PVME microgels were used in the oxidation polymerization of pyrrole, large PPy fibrils (appr. 400nm) were formed. Needle-like particles were formed due to the porous structure of microgels, which play a template role in the pyrrole polymerization process. When poly(VCL/AAEM) microgels were used as a template for oxidative polymerization of pyrrole, "raspberry-like" composite particles will be formed with PPy domains located in swollen hydropholic particle shell. Obtained stable composite microgels show similar thermal sensitivity as poly(VCL/AAEM) particles with fully reversible collapse-swelling properties. Increase of PPy content in composite particles increases conductivity of the composite material. The conductivity of composite particles prepared in water was much higher than that of prepared in water : ethanol mixtures. Furthermore, monodisperse PS-PEGMA particles, which were prepared in water medium by polymerization with sodium peroxydisulfate have been used as a template for deposition of polypyrrole (PPy). Obtained composite particles possess core-shell morphology where shell is composed out of small PPy nano-domains. The shell thickness can be varied by changing PPy load, controlling the overall template surface area in the system, and by influencing the pyrrole polymerization kinetics in presence of different oxidants. The last possibility provides also incorporation of different anions into polypyrrole shell. The stability of composite particles decreases gradually if the deposited PPy amount increases. It has been established that obtained particles are intrinsically coloured and the colour can be changed by the PS-PEGMA core size. Conductivity measurement shows that PS/PEGMA/PPy composite particles prepared by using phosphomolybdate as the oxidant are much more conductive than the particles prepared by the other two oxidants. The conductivity increases with the increase of PPy load in the system. Overall, the proper design of the template should give a possibility to control effectively the morphology, particle size and provide sufficient stability to the composite particles. Different morphologies, such as spherical, core-shell, raspberry and needle-like, with different particle size are expected to be available in different cases. By choosing the dopant anion or oxidation agent it is possible to vary the conductivity of the polymer. The stable water-based dispersions are expected to be used as additives for paint formulations, in electrorheology, microelectronic, ion-separation or disease diagnostics.

Le confinement de polymères incompatibles au sein de particules induit une séparation de phase et conduit à la formation de morphologies particulières (cœur-écorce, hémisphérique…). Cette nanostructuration est à l’origine de propriétés de filmification particulières qui justifient l’utilisation des particules polymères composites dans le cadre d’applications comme la formulation de peintures ou de revêtements. Ce travail s’intéresse au développement d’approches permettant de préparer ces particules polymères composites en une seule étape et en milieu aqueux. La stratégie proposée repose sur le couplage « en simultané » de deux polymérisations distinctes: la polymérisation de cyclooléfines par métathèse (ROMP) et la polymérisation radicalaire par transfert d’atome (ATRP). Après avoir mis en évidence les difficultés liées au couplage de la ROMP et de l’ATRP en milieu dispersé aqueux, deux approches originales faisant intervenir respectivement des conditions de miniémulsion et de microémulsion sont proposées. Pour chacune d’elles, la présentation du principe de la synthèse et l’analyse de ses résultats précèdent l’étude morphologique des particules produites. / So as to broaden the scope of their applications in paints, coatings and impact-resistant plastics, many investigations have been dedicated to the preparation of nanostructured colloids over the past decades. Original morphologies including core-shell, hemispherical and complex occluded structures (raspberry-like, golf ball-like, octopus-like) can now be readily prepared. This work proposes a new straightforward one-pot, one-step, one-catalyst strategy to prepare polymer composite particles based on the simultaneous combination of two mechanistically distinct polymerizations in aqueous dispersed media. Norbornene (NB) and methyl methacrylate (MMA) were converted via Ring-Opening Metathesis Polymerization (ROMP) and Atom-Transfer Radical Polymerization (ATRP), respectively. Two original routes, designed to ensure simultaneous ROMP and ATRP, respectively under mini- and microemulsion conditions, are proposed. Both are successively reviewed on chemical and colloidal levels. Specific attention is paid to the morphologies of the prepared particles.