Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / NanopartÃculas de FeCo recobertas com (Fe,Co)3O4 (Magnetita dopadas com cobalto) na estrutura casca caroÃo (Core-Shell), foram sintetizadas pela rota quÃmica conhecida como Sol-Gel Proteica. Os materiais sintetizados foram caracterizados por Termogravimetria (TG), DifraÃÃo de Raios-X (DRX), Magnetometria de Amostra Vibrante (VSM), Espectroscopia MÃssbauer, Microscopia EletrÃnica de Varredura (MEV) e Microscopia EletrÃnica de TransmissÃo (MET). Os resultados mostram que o aumento da temperatura de re-oxidaÃÃo influi diretamente no tamanho da casca (Shell) bem como o aumento da razÃo entre a magnetizaÃÃo remanente pela magnetizaÃÃo de saturaÃÃo. O efeito de Exchange Spring e Exchange Bias foram observados nas curvas de histerese. A estrutura Core-Shell foi formada de maneira nÃo homogÃnea, ou seja, nem todas as partÃculas foram recobertas pela magnetita. / FeCo Nanoparticles coated with (Fe,Co)3O4 (Magnetite doped with cobalt) were synthesized by the chemical route known as Sol-Gel Protein. The synthesized materials were characterized by thermogravimetry (TG), X-Ray Diffraction (XRD), Vibrating Sample Magnetometry (VSM), MÃssbauer spectroscopy, Scanning Electronic Miscroscopy (SEM) and Transmission Electronic Microscopy (TEM). The results show that the increase in temperature directly influences the size of the shell (Shell) and increased the ratio of remanent magnetization to the saturation magnetization. The effect of Exchange Spring and Exchange Bias were observed in the hysteresis curves. The Core-Shell structure was formed a non-homogeneous manner, ie not all the magnetite particles were coated.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2015-10-20T11:38:47Z No. of bitstreams: 2 Dissertação - Ariadne Canedo Eduardo - 2015.pdf: 1635500 bytes, checksum: 5c68f75920a8fc69b6de996110938818 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2015-10-20T11:40:09Z (GMT) No. of bitstreams: 2 Dissertação - Ariadne Canedo Eduardo - 2015.pdf: 1635500 bytes, checksum: 5c68f75920a8fc69b6de996110938818 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2015-10-20T11:40:09Z (GMT). No. of bitstreams: 2 Dissertação - Ariadne Canedo Eduardo - 2015.pdf: 1635500 bytes, checksum: 5c68f75920a8fc69b6de996110938818 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2015-02-26 / In recent years, research in the nanocomposites area of core-shell type increased significantly. The core-shell type nanoparticles with photoluminescence properties (PL) attract much attention from the scientific community. Are also of great interest nanoparticles that exhibit the upconversion energy, i.e. they absorbing low energy photons and emission high-energy photons. The present work has as objective nanocomposites synthesis of core-shell type, with CaTiO3 matrix (CT) and doped with rare earth ions Er3+ and Yb3+ in a variety composition and variations, to analysis the photoluminescent properties. The nanoparticles of the core and shell were obtained by the Method of Polymeric Precursors. The samples were characterized by X-ray diffraction (XRD) for structural characterization, and it was found that All samples presented the perovskite structure of the orthorhombic type. The characterization by Transmission Electron Microscopy (TEM) failed to demonstrate the formation of core-shell, requiring analysis by Energy Dispersive X-ray (EDX), which showed the presence of rare earth Er3+ and Yb3+ in the different layers. The UV-Vis gap allowed the calculation of the shell and core samples. The PL emission results were used to relate the thickness of the shell and the intensity of the emission. On the other hand, to study the upconversion energy, core materials showed a higher intensity than in the core-shell; the best intensity in the core-shell was found with doping the core with Yb3+ and Yb3+ with shell and Er3+ suggesting the transfer of energy between the layers. / Nos últimos anos, pesquisas na área de nanocompósitos do tipo core-shell cresceram significativamente. Atualmente nanopartículas do tipo core-shell com propriedades fotoluminescente (FL) atraem muita atenção da comunidade científica. Também são de grande interesse nanopartículas que apresentam a conversão ascendente de energia, ou seja, absorção de fótons de baixa energia e emissão de fótons de alta energia. O presente trabalho teve como objetivo a síntese de nanocompósitos do tipo core-shell, com a matriz CaTiO3 (CT) e dopagem com os íons terras raras Er3+ e Yb3+ nas mais variadas composições, para análise da propriedade fotoluminescente. As nanopartículas do core e do shell foram obtidas pelo Métodos dos Precursores Poliméricos. As amostras foram caracterizadas por Difração de Raios X (DRX) para caracterização estrutural, e foi constatada que todas as amostras apresentaram a estrutura perovsquita do tipo ortorrômbica. A caracterização por Microscopia Eletrônica de Transmissão (MET) não foi conclusiva quanto a formação do core-shell, sendo necessária a análise por Energia Dispersiva de Raios X (EDX), na qual verificou-se a presença das terras raras Er3+ e Yb3+ nas diferentes camadas. A espectroscopia de UV-Vis permitiu o cálculo do gap para as amostras core e shell. Os resultados de emissão FL foram utilizados para relacionar a espessura do shell e a intensidade da emissão. Por outro lado, ao estudar a conversão ascendente de energia, os materiais core apresentaram maior intensidade do que no core-shell; a melhor intensidade no core-shell foi verificada com a dopagem do core com Yb3+ e do shell com Yb3+ e Er3+, sugerindo a transferência de energia entre as camadas.

A utilização de nanopartículas (NP) magnéticas em várias áreas da biomedicina e biotecnologia vem recebendo elevado destaque nos últimos anos, graças à versatilidade de aplicações tais como: reparo de tecidos, diagnósticos, imagens por ressonância magnética, tratamento contra o câncer, separação celular, transporte controlado de drogas, entre outras. Atualmente, as NP com potencialidade de aplicação em biomedicina baseiam-se principalmente em óxidos magnéticos de ferro, os quais apresentam comportamento superparamagnético a temperatura ambiente e baixa magnetização da ordem de 60 emu g-1. A utilização dos óxidos se baseia em duas razões principais: facilidade e versatilidade de modificação da superfície e funcionalização devido aos grupos hidroxila na superfície das NP e pela baixa toxicidade comparada às NP magnéticas metálicas. Biocompatibilidade e funcionalidade específica são obtidas geralmente pela incorporação de materiais paramagnéticas e/ou diamagnéticos na superfície das NP contribuindo para diminuir ainda mais o baixo valor de magnetização de saturação dos óxidos. Nesse contexto, é necessário o desenvolvimento de novos núcleos magnéticos com elevado valor de magnetização, próximos aos valores observados para ferro metálico (~200 emu g-1). Entretanto, esses valores são observados apenas em NP metálicos com elevada toxicidade. Assim, neste trabalho, NP magnéticas bimetálicas de FePt, CoPt e NiPt recobertas óxido de ferro ou ferritas de Co e Ni foram sintetizadas pelo processo poliol modificado combinado com a metodologia de crescimento mediado por semente. As NP obtidas apresentaram tamanho e distribuição de tamanho compatíveis para aplicações biomédicas e a magnetização de saturação dos diferentes sistemas foi intensificada quando comparada às de NP de óxidos magnético puros. Os surfactantes ácido oleico e oleilamina presentes na superfície das NP como sintetizadas foram substituídos por moléculas de APTMS (3-aminopropiltrimetoxisilano) resultando em sistemas de NP dispersáveis em água. Adicionalmente, moléculas de carboximetil-dextrana foram conjugadas com as moléculas de APTMS modificando a superfície das NP e levando a formação de sistemas de NP magnéticas biocompatíveis, com estabilidade em dispersões aquosa e resposta magnética melhorada. As NP sintetizadas apresentam, em resumo, grande potencialidade para diversas aplicações em biomedicina. / In recent years, the magnetic nanoparticles uses in many biomedical and biotechnological areas have received great attention due to their applications possibilities such as: tissue repair, diagnostics, magnetic resonance imaging, cancer treatment, cell separation, and controlled drug delivery, among others. Today, the magnetic nanoparticles applications are mainly based on magnetic iron oxides, which exhibit superparamagnetic behavior at room temperature and low saturation magnetization around 60 emu g-1. Magnetic oxide uses was based in two main reasons: easily and versatility of surface changes and functionalization due to hydroxyl groups present on the oxide nanoparticles surface, and low toxicity compared with the magnetic metallic nanoparticles. Biocompatibility and targetable functionalizations are generally obtained by paramagnetic and/or diamagnetic materials incorporations onto the nanoparticle surface contributing to decreases the already low oxide saturation magnetization. In this context, the development of new magnetic nuclei with high magnetizations values closed to the metallic iron values (~200 emu g-1) is required. However, this value is only generally observed in highly toxic metallic nanoparticles. Therefore, in this study, bimetallic magnetic nanoparticles of FePt, CoPt and NiPt coated with iron oxide and Ni- or Co-ferrites in a core-shell structure are synthesized by using the modified polyol process combined with the seed-mediated growth method. Obtained nanoparticles presented size and size distribution compatible for biomedical applications and the saturation magnetization of the different synthesized systems were enhanced compared with the pure magnetic oxide nanoparticles. Oleic acid and oleylamine present on the as-synthesized magnetic nanoparticles surface were properly changed by (3-aminopropyl)trimethoxysilane (APTMS) molecules leading to water-dispersible magnetic nanoparticles system. In addition, carboxymethyl-dextran molecules were conjugated with the APTMS molecules changing the nanoparticles surfaces and resulting in biocompatible water-soluble magnetic nanoparticles systems with improved magnetic response. These synthesized biocompatible magnetic systems present a great potential for many biomedical applications.

Nanomateriais apresentam propriedades ajustáveis pelo seu tamanho e forma, como o fenômeno de superparamagnetismo em nanopartículas magnéticas ou o confinamento quântico dos portadores de carga em pontos quânticos (quantum dots). Assim, a síntese de nanopartículas esféricas monodispersas torna-se um fator extremamente importante, haja visto que tais propriedades podem ser ajustáveis para diferentes aplicações na área de tecnologia e biomedicina. Nanopartículas magnéticas e quantum dots podem ser apontados como promissores materiais para diagnóstico e terapia de neoplasias (câncer), e o desenvolvimento desses sistemas busca, atualmente, intensificar a magnetização e a eficiência de emissão, respectivamente, relativo às propriedades magnéticas e ópticas, além de outros requisitos. Neste trabalho, nanopartículas esféricas de cobalto metálico foram sintetizadas com diâmetro médio de 5,3 nm e desvio padrão de 0,4 nm, distribuição de tamanhos lognormal. A equação de Langevin modificada pelo modelo de partículas interagentes foi utilizada no ajuste da curva de magnetização M(H) para obtenção do diâmetro magnético médio e desvio padrão, 4,7 nm e 1,0 nm, respectivamente. Comparando os dois diâmetros, encontra-se uma camada morta de magnetização de aproximadamente 3,0 Å a qual, praticamente, não contribui para a magnetização da amostra, sendo a magnetização de saturação de 125 emu g-1. Nanoestruturas core/shell de Co/Au apresentaram a propriedade de ressonância plamon de superfície, uma propriedade adicional também desejada para aplicações biomédicas, sendo este sistema denominado magnetoplasmônico. Quantum dots de CdSe foram sintetizados como elevado controle de tamanho e forma. Utilizando rotas de síntese diferentes dos clássicos procedimentos denominados TOP-TOPO, e dióxido de selênio como precursor, estudos mostraram que na presença de um agente redutor no meio de reação e do solvente 1-octadeceno, as amostras apresentaram melhores propriedades óticas. A estrutura cristalina das amostras de CdSe corresponde à formação da fase blenda de zinco, diferentemente das sínteses TOP-TOPO que levam à formação da fase hexagonal wurtzita. A cinética de crescimento dos quantum dots de CdSe também foram avaliadas através de alíquotas retiras com o tempo de reação mostrando um crescimento exponencial do diâmetro das partículas, como previsto pelas teorias de nucleação e crescimento. Estudos por microscopia de fluorescência mostraram que os quantum dots apresentaram o comportamento de intermitência de fluorescência relatado na literatura como um dos fatores que levam a uma diminuição do rendimento quântico de fluorescência. Nanoestruturas core/shell de CdSe/ZnS foram obtidas com elevado controle da espessura da camada de recobrimento e a intensificação das propriedades de fotoluminescência foram mostradas. Os objetivos do trabalho foram alcançados com sucesso, onde foi possível observar a estabilização e a intensificação da magnetização da fase de cobalto metálico, pouco relatado na literatura. Ainda, foi possível conferir maior estabilidade química, versatilidade de funcionalização da superfície e uma segunda propriedade de ressonância plasmônica com o recobrimento com ouro, sem grande prejuízo da propriedade magnética. Em relação aos sistemas ópticos, os semicondutores de CdSe foram obtidos por nova rota de síntese com expressivo controle de tamanho e forma, recobertos com ZnS intensificando as propriedades ópticas do sistema.  / Nanomaterials properties are size- and shape-controlled, such as the superparamagnetism phenomenon of magnetic nanoparticles or the quantum confinement of charge carriers of quantum dots. Therefore, synthesis of monodisperse spherical nanoparticles became extremely important over the past few deacades, since nanoparticles can be used for plenty of applications in technology and biomedicine. Magnetic nanoparticles and quantum dots are promising materials for diagnosis and therapy of cancer. Spherical nanoparticles of metallic cobalt were synthesized with mean diameter of 5,3 nm and standard deviation of 0,4 nm, lognormal distribution. A modified Langevin equation using the interacting superparamagnetic model was used to fit magnetization curves obtaining the mean magnetic diameter and standard deviation, 4,7 nm and 1,0 nm, respectively. The difference between these two diameters was assigned to the magnetic dead layer (∼3.0 Å), which does not contribute to the sample magnetization, being the saturation magnetization of cobalt nanoparticles around 125 emu g-1. Co/Au core/shell nanostructures were synthesized and the surface plasmon ressonance property was observed, an additional property also desired for biomedical applications, being the Co/Au core/shell system called magnetoplasmonic. CdSe quantum dots were synthesized with high size- and shape-controlled. Using different synthetic routes from the classic TOP-TOPO synthesis, and selenium dioxide as a precursor, the results show that and reducing agent is necessary and 1-octadecene solvent leads to better optical properties. CdSe samples showed a zinc blend (cubic phase) crystal structure, different from TOP-TOPO syntheses that leads to wurtzite structure (hexagonal phase). The growth kinetics of CdSe particles were also evaluated through aliquots from reaction showing exponential growth of particles diameter, as predicted on the theory of nucleation and growth. Fluorescence microscopy studies showed that quantum dots exhibited fluorescence intermittence behavior already reported in the literature as one fo the reasons for the quantum yield decrease. CdSe/ZnS core/shell nanostructures were obtained with high control of the coating layer thickness and the increase of the photoluminescence properties were shown.

Koherent Diffraktionsavbildning med en intensiv röntgenpuls från en Frielektronlaser har möjliggjort strukturbestämning av isolerade nanopartiklar som inte går att studera med hjälp av konventionella metoder, så som elektronmikroskopi. En mycket kort pulslängd tillsammans med spridningssignalens beroende av objektets elektroniska struktur medför också möjligheten att studera inducerad ultrasnabb dynamik med denna teknik. I detta projekt studerades joniseringspåverkan av Xe hos Xe-Ar core-shell-nanokluster. Enligt teorin har neutral Xe lägre spridningstvärsnitt under dess 3d-resonans än det motsvarande för fotonenergier över 3d-resonansen. Därför var en hög kontrast i klustren förväntad vid energier över dess 3d-resonans. I stället observerades mörkare regioner liknande hål i rekonstruktioner från de experimentella resultaten vid energier över 3d-resonansen hos Xe. En möjlig förklaring var jonisering av neutral Xe. För att undersöka detta skapades 3D modeller av Xe-Ar nanokluster för att simulera den interaktionen mellan intensiva röntgenpulser och nanokluster. Diffraktionsmönstren som genererades med hjälp av 3D-modellerna användes sedan för att utföra Iterativ fasrekonstruktion och rekonstruera partikeldensiteten. Brytningsindex av neutral Xe och de första tio jontillstånden hos Xe beräknades med hjälp av en modell konstruerad i detta projekt, kallad för step-model. Följaktligen introducerades samtliga jontillstånden hos Xe från 0 till 10 in i 3D modeller av Xe-Ar nanoklustren med brytningsindexen av jontillstånden uppskattade med hjälp av Kramers-Kronig-relationerna. Här antogs det att samtidigt som resonansen för varje Xe-jon förflyttas visar 𝛽 (det vill säga den imaginära komponenten i det komplexa brytningsindexet) som en funktion av fotonenergin, ett icke-monotoniskt beteende med en förändring i fotonenergin. Simuleringsresultaten erhållna med hjälp av Kramers-Kronig-relationerna visade en avtagande trend för 𝛽 i Xe-joner med en laddning> 4+ till skillnad från en ökning i 𝛽 för joner med en laddning <4+ relativt dess motsvarande för neutral Xe. Denna metod ansågs tillräcklig för att användas som en första approximation. Dessa resultat visade att ju mer Xe joniseras (och därför minskar 𝛽) desto mer transparenta blir Xe-jonerna under en laserpuls och därför ser de mörkare ut jämfört med Ar som har sin resonans långt ifrån fotonenergierna relevanta för detta projekt (660–760 eV). Vidare simulerades temporära förändringar i Xe-jonpopulationer för att bekräfta de erhållna simuleringsresultaten via step-model. En massiv energideposition då den intensiva röntgenpulsen träffar Xe-kärnorna initierar en serie av joniseringsmekanismer under de första få femtosekunderna av pulsen. Simuleringar för de jonpopulationer som uppstår och försvinner under förloppet av en 100 femtosekunder-lång röntgenpuls visade att jontillstånd mellan 1+ och 10+ är redan förbrukade efter några få femtosekunder vid 1016 W/cm2. Vid slutet av pulsen observerades endast högt laddade Xe-joner (upp till 35+). Den slutsats som drogs var därför att mörkare regioner som liknade hål och observerades i rekonstruktioner från experimentella data var en konsekvens av en förflyttning av resonansen hos de högt laddade Xe-joner (>4+) relativt dess motsvarande i en neutral Xe så att deras spridning minskar. / Coherent Diffraction Imaging with intense x-ray pulses from X-ray Free-Electron Lasers has enabled structure determination of isolated nanoparticles, that cannot be studied with conventional methods, such as electron microscopy. The very short pulse durations and the intrinsic dependence of the scattering signal on the electronic structure of the scattering object also allow studying ultrafast light-induced dynamics with this technique. In this project, the ionization impact of Xe on Xe-Ar core-shell nanoclusters was studied. Theory predicts that neutral Xe has a lower scattering cross-section below its 3d resonance than that at photon energies above its 3d resonance. Therefore, a high contrast in clusters above the neutral Xe’s 3d resonance is expected. However, in the experimental data, unusual dark features resembling holes were observed at energies above Xe’s 3d resonance. As possible explanation, ionization of neutral Xe was suggested. To investigate this, 3D models of Xe-Ar nanoclusters were created to simulate the interaction of intense x-ray pulses and nanoclusters. The diffraction patterns generated by these 3D models were used to perform Iterative Phase Retrieval to reconstruct the particle densities. The refractive indices of neutral Xe and Xe’s first ten ionic states were computed using a model designed in this project, called the step-model. Hence, each and every ionic state of Xe from 0 to 10 were introduced into the 3D models of the Xe-Ar nanoclusters with refractive indices of the ionic states estimated based on the Kramers-Kronig relations. Here, it was assumed that as the resonance is shifting for every ionic state of Xe, 𝛽 (i.e the imaginary component of the complex refractive index) as a function of photon energy shows a nonmonotonic behavior as the photon energy is varied. The simulation results by Kramers-Kronig relations showed a decrease in 𝛽 for ionic states > 4+ in contrast to an increase in 𝛽 for ions with charges < 4+ relative to that of neutral Xe. This approach was sufficient to be used as a first approximation. The results showed that Xe ions become more transparent to the laser pulse as their charge increases (and 𝛽 thereby decreases) and therefore they appear darker than Ar, which has its resonance far away from photon energies relevant for this project (660–760 eV). Furthermore, temporal changes in ionic populations of Xe were simulated to confirm the simulation results obtained by the step-model. The massive energy deposition upon interaction with the intense laser pulse launches a series of ionization events in the Xe cores during the first few fs of the x-ray pulse. The simulation of ionic populations emerging and depleting during the 100-fs-long 1016 W/cm2 x-ray pulse showed that ionic states 1+ to 10+ are depleted already after a few fs. By the end of the pulse, only highly charged (up to 35+) Xe ions are observed. Therefore, it was concluded that the dark features resembling holes in reconstructions from the experimental data were a consequence of a shift in the resonance of highly charged Xe ions (>4+) relative to that of neutral Xe so that their scattering decreases.

Existing commercially available microcarriers are very efficient at encouraging cell attachment and proliferation. However, recovery of the cells is problematic as it requires the use of proteolytic enzymes which are damaging to critical cell adhesion proteins. From this perspective, temperature responsive polymers appear to be a valid option. The current innovative study is to produce and engineer microcarriers in terms of particle size, surface coating and properties, as well as thermo-responsiveness for cell release. All these benefits are based on particle production by membrane emulsification to provide a highly controlled particle size. The polymer of choice is poly N-isopropylacrylamide (pNIPAM) because of the sharpness of its phase transition, biocompatibility and transition temperature close to the physiological value. These characteristics make pNIPAM a very attractive material for Tissue Engineering applications. Cells are cultured on the hydrophobic surface at 37??C and can be readily detached without using proteolytic enzymes from the surface by lowering the temperature to room temperature. The Dispersion Cell (MicroPore Technologies Ltd, UK) was successfully employed for the production of W/O emulsions. The generated monomer droplets were additionally solidified by applying a free radical polymerisation to manufacture solid pNIPAM microspheres. Additionally, calcium alginate particles were also generated and further functionalised with amine terminated pNIPAM to form temperature responsive core-shell particles by simply taking advantage of the electrostatic interactions between the carboxyl groups of the alginate and amino groups of the modified pNIPAM. Controlled particle production was achieved by varying process parameters and changing the recipe formulation (e.g. monomer concentration, surfactant concentration, pore size and inter-pore spacing, injection rate, shear stress applied at the membrane s surface). The manufactured particles were then analysed in terms of particle size and size distribution, chemical composition, surface analysis, shrinkage ratio and thermo-responsiveness and further sterilised and used for cell culture and release experiments. Swiss Albino 3T3 fibroblastic cells (ATCC, USA) were utilised to show proof-of-concept for this technology. Cell attachment and proliferation were assessed and successfully demonstrated qualitatively and quantitatively. pNIPAM solid particles, uncoated and with different protein coatings were shown to allow a limited degree of cell attachment and proliferation compared to a commercially available microcarrier. On a different approach, uncoated core-shell structures demonstrated improved capabilities for cell attachment and proliferation, similar to commercially available microcarriers. Having in mind the potential of temperature responsive polymers and the aim of this innovative study, cell detachment from the generated microcarriers was evaluated and compared to a commercially available temperature responsive surface. Necessary time for detachment was recorded and detached cells were recovered and reseeded onto tissue culture plastic surfaces in order to evaluate the replating and reattachment capabilities of the recovered cells. Successful cell detachment was achieved when using the core-shell structures as cell microcarriers, but the necessary time of detachment was of an order higher than that for the commercial temperature responsive surface.

Thesis (PhD)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The synthesis of structured nanoparticles, in particular core/shells, IS of great technological and economical importance to modem materials science. One of the advantages of structured particles is that they can be synthesized with either a solid core (albeit soft or hard) or a liquid core (of varying viscosity). This adds to the versatility of structured particles and their relevance to a majority of industrial and commercial endapplications. The synthesis of core/shell particles with liquid cores was investigated for the effective impact modification of glassy amorphous polymers. Polybutyl acrylate was chosen as the shell due to its rubbery nature. Hexadecane functioned as the core oil and facilitated osmotic stability by being a suitable hydrophobe for the miniemulsion synthesis. Polymer synthesis was preceded by the prediction of particle morphology by using thermodynamic prediction models. Core/shell particles with liquid cores were synthesized via miniemulsion polymerization. This resulted in the direct introduction of core-oil and monomer into the miniemulsion droplets. Polymerization was achieved in situ, resulting in the formation of particles with the desired morphology. For additional strength, stability and matrix mixing capabilities, methyl methacrylate (MMA) was grafted onto the initial core/shell particles. The obtained morphology was in contradiction with the predicted morphology, thus pointing to strong kinetic influences during the polymerization process. These influences could be attributed to surface anchoring of polymer chains due to the initiator (KPS) used, the establishment of the polymerization locus as well as the increase in viscosity at the polymerization locus. To test these influences a surface-inactive initiating species (AIBN) and an interfacial redox initiating species (cumyl hydroperoxide/Fe/") were used. Use of the former resulted in the formation of solid polymer particles due to homogeneous polymerization throughout the droplet, thus leading to an inverse core/shell morphology as a result of thermodynamic considerations. The redox initiator promoted kinetic influences as a result of fast polymerization kinetics at the droplet/water interface. This, as well as the increase in viscosity, facilitated the production of core/shell particles. To obtain core/shell particles with the desired size, the influence of surfactant concentration was investigated. Capillary hydrodynamic fractionation (CHDF) was used to determine the particle size of the initial core/shell particles as well as the size of the MMA-grafted core/shell particles. The area stabilized per surfactant molecule was calculated stoichiometrically and compared to "classical" miniemulsion results, i.e. data generated from the synthesis of polymeric latexes in the presence of a hydrophobe, but at a much lower hydrophobe:monomer ratio than was used here. The influence of methanol as well as the possibility of scaling-up the process was also investigated. The study was further expanded to the investigation of living miniemulsion polymerization techniques to control the molecular architecture of synthesized core/shell latexes. The influence of different RAFT agents, initiators and monomers were investigated on the core/shell formation properties of the investigated systems. The combined effects of establishing the polymerization locus as well as increased polymerization kinetics, thus increasing the viscosity at the polymerization locus, lead to the successful formation of liquid- filled core/shell particles. To conclude, the ability of the synthesized core/shell particles to induce impact modification in glassy amorphous polymers was investigated. Results showed that incorporation of these particles could effectively modify the intrinsic properties of the investigated polymers, resulting in a brittle-to-ductile transition. Improved impact results of the investigated glassy matrix were obtained. Keywords: core/shell, liquid-filled, RAFT, miniemulsion, impact modification / AFRIKAANSE OPSOMMING: Die sintese van gestruktureerde nano-partikels, meer spesifiek kern/skil partikels, is van onskatbare tegnologiese en ekonomiese belang vir moderne materiaalkunde. Een van die voordele van hierdie tipe partikels is dat sintese kan geskied met 'n soliede kern (hard of sag) of vloeistofkern (met wisselende viskositeit). Dit dra by tot die veelsydigheid van gestruktureerde partikels en dus tot grootskaalse aanwending in industriële en kommersiële toepassings. Die sintese van kern/skiI partikels met vloeistofkerne is ondersoek met die oog op effektiewe slagsterkte modifikasie van glasagtige amorfe polimere. Polibutielakrilaat is gekies as skil-polimeer op grond van sy rubberige voorkoms. Heksadekaan moes funksioneer as die kern-olie, maar het ook bykomende osmotiese stabiliteit verleen tydens die miniemulsie-polimerisasie proses. Dit is as gevolg van die gepaste hidrofobiese eienskappe van heksadekaan. Polimeer sintese is voorafgegaan deur die voorspelling van partikel morfologie met behulp van termodinamies gebaseerde voorspellingsmodelle. Kern/skil partikels is gesintetiseer deur middel van 'n miniemulsie-polimerisasie reaksie wat die direkte inkorporering van kern-olie en monomeer in die miniemulsiedruppel teweeg bring. Polimerisasie vind in situ (lat. vir in die oorspronklike plek, m.a.w. binne-in die druppel) plaas en lei tot die vorming van partikels met die gewenste morfologie. Metielmetakrilaat is ge-ent op die oorspronklike kern/skil partikels om addisionele sterkte, stabiliteit en vermenging met die matriks polimeer te bewerkstellig. Die verkrygde morfologie is teenstrydig met die voorspelde morfologie, wat dus die teenwoordigheid van sterk kinetiese invloede aandui. Hierdie invloede kan toegeskryf word aan die oppervlak-aktiewe afsetter (KPS, kaliumpersulfaat) wat gebruik is, die daarstelling van die polimerisasie lokus asook die toename in viskositeit by die lokus van polimerisasie. Om hierdie invloede te toets is 'n oppervlak-onaktiewe afsetter (AIBN, asobisisobutironitriel) en intervlak redoks-afsetter (kumielhidroperoksied/Pe'") gebruik. Gebruik van eersgenoemde het die vorming van soliede partikels teweeg gebring. Dit is as gevolg van homogene polimerisasie in die druppel en dus die ontstaan van omgekeerde kern/skiI partikels weens termodinamiese oorwegings. Die redoks-afsetter het egter die kinetiese oorwegings bevoordeel as gevolg van vinnige polimerisasiekinetika by die druppel/water intervlak. Dit, tesame met die toename in viskositeit, maak die produksie van kern/skil partikels moontlik. Vir die verkryging van kern/skiI partikels met die gewenste partikelgrootte is die invloed van die seep konsentrasie ondersoek. CHDF (eng. capillary hydrodynamic fractionation) is gebruik om die partikelgrootte van die oorspronklike kern/skiI partikels, sowel as dié ge-ent met metielmetakrilaat, te bepaal. Die area gestabiliseer per seepmolekule is bereken d.m.v. stoichiometrie en vergelyk met "klassieke" miniemuisie data, d.i. data verkry deur die sintese van latekse in die teenwoordigheid van 'n hidrofoob, maar teen 'n baie laer hidrofoob:monomeer-verhouding as wat hier gebruik is. Die invloed van metanol, asook die moontlikheid om die reaksie op te skaal, is ondersoek. Die studie is verder uitgebrei om die invloed van lewende miniemulsie-polimerisasie tegnieke in te sluit, om sodoende beheer uit te oefen oor die molekulêre argitektuur van die gesintetiseerde latekse. Die invloed van verskeie RAFT (eng. reversible additionfragmentation chain transfer) agente, afsetters en monomere op die kern/skiI vormingsmoontlikhede van die bestudeerde stelsels, is ondersoek. Die gesamentlike effek van die daarstelling van die polimerisasie lokus en dus die verhoging van die viskositeit by die lokus, lei tot die suksesvolle vorming van vloeistof-gevulde kern/skiI partikels. Laastens is die invloed van die gesintetiseerde kern/skil partikels op die slagsterkte van glasagtige amorfe polimere ondersoek. Resultate dui daarop dat die insluiting van hierdie partikels kan lei tot die effektiewe verandering van die intrinsieke eienskappe van die bestudeerde polimere, en dus 'n oorgang van bros na rekbaar kan veroorsaak. 'n Verbetering in die slagsterkte resultate van die bestudeerde glasagtigte matriks is ook waargeneem.

Cette thèse est divisée en trois parties. La première traite la synthèse de la polyaniline (PANI), un polymère conducteur de trou, utilisé dans plusieurs applications. En variant les quantités du monomère et de l'oxydant tout en fixant leur rapport molaire à 1:1,25, et en ajoutant de l'oxyde de magnésium, des aiguilles et des nouvelles structures semblables aux échinides sont formées. Le mécanisme de formation des structures unidimensionnelles est expliqué à l'aide de la théorie des multicouches. La deuxième partie est consacrée à la fabrication des monocouches photovoltaïques à faible coût en se basant sur le principe de fonctionnement des cellules à pigment photosensible (en anglais DSSC, Dye-Sensitized Solar Cell). En 1991, Grätzel a réintroduit l'effet photo-électrochimique en développant la première DSSC, une des cellules solaire troisième génération, formée d'un film de TiO2 (photo-anode) pigmenté à l'aide d'un colorant et d'un électrolyte qui sert à régénérer le pigment oxydé. Malgré leur faible coût, les DSSCs font face à de nombreux problèmes tels que le coût élevé du pigment, la fuite de l'électrolyte, la sublimation du couple I-/I3- à travers I2, etc. Afin de résoudre ces problèmes, des monocouches photovoltaïques ont été développées. Des composites formés de PANI et TiO2 sont la base de ces dispositifs nouvelle génération. La polymérisation in-situ de l'aniline en présence des nanoparticules de TiO2 conduit à une forte interaction entre la PANI et les particules de TiO2 où une structure " core (TiO2)/shell (PANI) " existe dans le composite. Dans le dispositif photovoltaïque basé sur le composite PANI-TiO2, PANI est considérée comme pigment à la photo-anode et comme poly-électrolyte plus profondément dans le composite. En plus, des textiles fabriqués utilisant ces composites photo-génèrent une tension de 0,6 V et un courant de 1 A/m2 lorsque l'éthanol est injecté dans le dispositif. Une nouvelle architecture a été développée qui sert à améliorer la performance de la cellule et en même temps stocker l'énergie pour des utilisations ultérieures. La dernière partie est consacrée à la fabrication des DSSCs basées sur les pigments naturels. L'anthocyane, un pigment naturel halochromique responsable de la couleur rouge dans les plantes, a été extrait du chou rouge et utilisé pour pigmenter les films de TiO2. Cette propriété se traduit par la fabrication des DSSCs de différentes couleurs et comportement photovoltaïque. Avec un pH égal à 0, une Vco et une Jcc de 520 mV et 185 μA/cm2 sont respectivement obtenues prouvant la possibilité d'utiliser le chou rouge comme source de pigment à très faible coût des DSSCs.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / Thesis presented in partial fulfilment of the requirements for the degree of Master of Science (polymer science) at the University of Stellenbosch / Embargo date 2010-03-31 plt 2010 / ENGLISH ABSTRACT: A novel method, herein referred to as ‘solvent facilitated coaxial electrospinning’, was used to produce reversibly thermochromic core-shell fibres with poly(methyl methacrylate) (PMMA) as shell and a thermochromic dye composite as core. The thermochromic dye composite consisted of combinations of 1-dodecanol, bisphenol A (BPA) and crystal violet lactone (CVL). In the ‘solvent facilitated coaxial electrospinning’ method, the thermochromic dye composite was dissolved in a suitable ‘facilitating solvent’ prior to spinning, instead of being spun into the fibres from the melt as previously described in literature. A low interfacial tension between the core and shell liquids, which is beneficial to effective core entrainment, was achieved by using a correctly chosen core ‘facilitating solvent’. The PMMA was dissolved to form the shell spinning liquid and by selecting the correct core and shell solvents, spinneret blockage and precipitation due to core and shell liquid interactions were eliminated. High molar mass PMMA was used to produce fibres with diameters in the range of 3–10 μm (larger than typical electrospun fibres) in order to minimize light scattering and subsequently allow visual observation of the thermochromic transitions, unlike the fibres that were produced in literature. The fibres were analyzed using SEM, TEM, TGA and DSC to investigate fibre morphology, dye composite thermal transition and fibre composition. Physical and chemical interactions between the thermochromic dye composite and the PMMA shell were identified as possible causes of differences between the thermochromic transition temperatures of the core-shell fibres and the bulk dyes, as well as of the instability of the colour developed state of certain thermochromic fibres. The spatial confinement of the dye composite inside the fibres and the extensive volume reduction (from bulk dye to small volume inside the fibres) affected the thermochromic behaviour of the thermochromic composite once it was entrained in the fibres. An excess BPA was used in the dye composition to allow the production of reversibly thermochromic fibres with a stable colour developed state. / AFRIKAANSE OPSOMMING: A nuwe metode, hierin beskryf as ‘oplosmiddel gefasiliteerde koaksiale elektrospinnery’, is gebruik om omkeerbare termochromiese kern-skil vesels met polie(metiel metakrilaat) (PMMA) as skil en ‘n saamgestelde termochromiese kleurmiddel as kern te vervaardig. Die saamgestelde termochromiese kleurmiddel het bestaan uit kombinasies van 1-dodekanol, bisfenol A (BPA) en kristal violet laktoon (CVL). Vir die ‘oplosmiddel gefasiliteerde koaksiale elektrospin’-metode, is die saamgestelde termochromiese kleurmiddel opgelos in ‘n gepaste ‘fasiliterende oplosmiddel’ voordat dit geëlektrospin is, eerder as om dit te smelt om dit sodoende in vesels te kan inspin soos beskryf in die literatuur. ‘n Lae raakvlakspanning tussen die kern- en skilspinvloeistowwe, wat voordelig is vir doeltreffende kern insluiting, is bereik deur gebruik te maak van sorgvuldig verkose ‘fasiliterende oplosmiddels’ vir die kern. Die PMMA is opgelos om die skilspinoplossing te vorm en, deur die keuse van die korrekte kern- en skiloplosmiddels, kon spinneret blokkasie en neerslag van die polimeer as gevolg van kern- en skilvloeistofinteraksies elimineer word. Hoë molekulêre massa PMMA is gebruik om vesels te vervaardig met deursnee in die omtrek van 3–10 μm (groter as tipiese elektrogespinde vesels) om sodoende lig-verstrooiing te verminder en daardeur visuele waarneming van die termochromiese oorgange moontlik te maak, in teenstelling met die vesels wat in die literatuur gevorm is. Die vesels is ge-analiseer met SEM, TEM, TGA en DSC om veselmorfologie, termiese omskakelinge van saamgestelde kleurmiddels en veselsamestelling te bestudeer. Fisiese en chemiese interaksies tussen die saamgestelde termochromiese kleurmiddel kern en die PMMA skil is geïdentifiseer as moontlike oorsake van verskille tussen die termochromiese oorgangstemperature van die kern-skil vesels en die kleurmiddels in grootmaat, asook van die onstabiliteit van die gekleurde toestand van sommige termochromiese vesels. Die ruimtelike inperking van die saamgestelde kleurmiddel binne in die vesels asook die beduidende volume verkleining (van grootmaat kleurmiddel tot klein volume binne in die vesels) het die termochromiese gedrag van die saamgestelde kleurmiddel binne die vesels beïnvloed. ‘n Oormaat BPA is in die saamgestelde termochromiese kleurmiddel gebruik om die produksie van omkeerbaar termochromiese vesels met ‘n stabiele gekleurde toestand toe te laat.

© Springer Science+Business Media Dordrecht 2016 / Reducing AgNO3 by glucose at basic pH coated the surface of silica spheres with a high density of hemispherical silver nanoparticles (average diameter 3.2±1 nm). A much lower silver concentration than is standard favored heterogeneous nucleation of silver on the silica surface at the expense of homogeneous nucleation in solution. The slow growth rate of the nuclei promoted the formation of discrete silver particles rather than a continuous shell. Based on scanning electron microscopy and transmission electron microscopy, the surface coverage of silver seed particles was as high as 25% at 10 °C without prior functionalization of the silica. The particles were composed of metallic silver based on x-ray photoelectron spectroscopy. There was a sharp increase in the silver surface coverage and decrease in the particle size when the temperature was raised from 5 °C to 10 °C and the amount of silica was decreased from 0.2 to 0.025 V/V. The size was controlled by the diffusion barrier through the ion shell surrounding the silica spheres and by maintaining reaction conditions where the particles on the surface compete for silver.