In this dissertation I present advances in the studies of artificial lattices with honeycomb topology, called artificial graphene (AG), in nano-patterned GaAs quantum wells (QWs). AG lattices with very small lattice constants as low as 40 nm are achieved for the first time in GaAs. The high quality AG lattices are created by optimized electron-beam (E-beam) lithography followed by inductively coupled plasma reactive-ion etching (ICP-RIE) process. E-beam lithography is used to define a honeycomb lattice etch mask on the surface of the GaAs QW sample and the optimized anisotropic ICP-RIE process is developed to transfer the pattern into the sample and create the AG lattices. Such high-resolution AG lattices with small lattice constants are essential to form AG miniband structures and create well-developed Dirac cones. Characterization of electron states in the nanofabricated artificial lattices is by optical experiments. Optical emission (photoluminescence) yields a determination of the Fermi energy of the electrons. A significant reduction of the Fermi energy is due to the nano-patterning process. Resonant inelastic light scattering (RILS) spectra reveal novel transitions related to the electron band structures of the AG lattices. These transitions exhibit a remarkable agreement with the predicted joint density of states (JDOS) based on the band structure calculation for the honeycomb topology. I calculate the electron band structures of AG lattices in nano-patterned GaAs QWs using a periodic muffin-tin potential model. The evaluations predict linear energy-momentum dispersion and Dirac cones, where the massless Dirac fermions (MDFs) appear, occur in the band structures. Requirements of the parameters of the AG potential to achieve isolated and well-developed Dirac cones are discussed. Density of states (DOS) and JDOS from AG band structures are calculated, which provide a basis to interpret quantitatively observed transitions of electrons involving AG bands. RILS of intersubband transitions reveal intriguing satellite peaks that are not present in the as-grown QWs. These additional peaks are interpreted as combined intersubband transitions with simultaneous change of QW subband and AG band index. The calculated JDOS for the electron transitions within the AG lattice model provide a remarkably accurate description of the combined intersubband excitations. Novel low-lying excitation peaks in RILS spectra, interpreted as direct transitions between AG bands without change in QW subband, provide a more direct insight on the AG band structures. We discovered that RILS transitions around the Dirac cones are resonantly enhanced by varying the incident photon energies. The spectral lineshape of these transitions provides insights into the formation of Dirac cones that are characteristic of the honeycomb symmetry of the AG lattices. The results confirm the formation of AG miniband structures and well-developed Dirac cones. The realization of AG lattices in a nanofabricated high mobility semiconductor offers the advantage of tunability through methods suitable for device scalability and integration. The last part of this thesis describes the growth of nanocrystalline single layer and bilayer graphene on sapphire substrates by molecular beam epitaxy (MBE) with a solid carbon source. Raman spectroscopy reveals that fabrication of single layer, bilayer or multilayer graphene crucially depends on MBE growth conditions. Etch pits revealed by atomic force microscopy indicate a removal mechanism of carbon by reduction of sapphire. Tuning the interplay between carbon deposition and its removal, by varying the incident carbon flux and substrate temperature, should enable the growth of high quality graphene layers on large area sapphire substrates.

Thesis (Ph. D.)--University of Canterbury, 2009. / Typescript (photocopy). Includes bibliographical references (p. 241-266). Also available via the World Wide Web.

Submitted by Milena Rubi (milenarubi@ufscar.br) on 2017-06-01T13:24:35Z No. of bitstreams: 1 PEREIRA_Tamyris_2015.pdf: 24726845 bytes, checksum: cad6e1bb20698eeb16bd6280b89c6c35 (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2017-06-01T13:24:52Z (GMT) No. of bitstreams: 1 PEREIRA_Tamyris_2015.pdf: 24726845 bytes, checksum: cad6e1bb20698eeb16bd6280b89c6c35 (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2017-06-01T13:24:59Z (GMT) No. of bitstreams: 1 PEREIRA_Tamyris_2015.pdf: 24726845 bytes, checksum: cad6e1bb20698eeb16bd6280b89c6c35 (MD5) / Made available in DSpace on 2017-06-01T13:25:07Z (GMT). No. of bitstreams: 1 PEREIRA_Tamyris_2015.pdf: 24726845 bytes, checksum: cad6e1bb20698eeb16bd6280b89c6c35 (MD5) Previous issue date: 2015-02-27 / Não recebi financiamento / This work focuses on the production of nanostructured films of poly (ethyleneimine) PEI together with MAO-b free and encapsulated in liposomes constructed by the layer-bylayer technique (LbL), for application in biosensors. Liposomes are microscopic vesicles composed of concentric lipid bilayers separated by aqueous medium, capable of encapsulating hydrophilic and/or hydrophobic molecules, which are, respectively, included in the aqueous compartment and the membrane or adsorbed. Enzymes encapsulated in liposomes have advantages in stability and catalytic activity compared to the free enzyme. Liposomes were synthesized by using a rotary evaporator and subsequently the enzyme was immobilized. The phospholipids dipalmitoyl phosphatidyl glycerol (DPPG) and palmitoyl oleoyl phosphatidyl glycerol (POPG) and the mixture of the two were used in this study in the ratio (1:1) and (1:4) (m/m). To build a biosensor in neurotransmitter monoamine oxidase b on, thin films were set up on poly (ethyleneimine) PEI together with monoamine oxidase b enzyme (MAO-B) immobilized or not in liposomes and deposited on ITO electrodes, being the Prussian blue a mediator of electrons. The obtained films were characterized by fluorescence spectroscopy, UV-visible and circular dichroism. The results indicated that the film is deposited successfully on quartz and ITO. The amperometric measurements were performed to detect the film sensitivity and the detection limits and check which architecture is best suited for the best composition of the biosensor. The results achieved until now show that the liposome retain the conformational structure of the enzyme and films composed of PEI / MAO-B + POPG:DPPG in proportion (1:4) (w/w) indicate better performance of the biosensor, due to the sensitivity value of 0.33 ± 0.02 µA.cm-2 mM-1 found and a good selectivity. / Este trabalho é centrado na produção de filmes nanoestruturados de poli (etilenoimina) PEI em conjunto com MAO-B livre e encapsulada em lipossomos, construídos através da técnica layer-by-layer (LbL), camada por camada, para aplicação em biossensores. Lipossomos são vesículas microscópicas compostas de bicamadas lipídicas concêntricas, separadas por um meio aquoso, capazes de encapsular moléculas hidrofílicas e/ou hidrofóbicas, que se encontram, respectivamente, no compartimento aquoso e inserida ou adsorvidas na membrana. Enzimas encapsuladas em lipossomos apresentam vantagens quanto à estabilidade e atividade catalítica em comparação com a enzima livre. Os lipossomos foram sintetizados por rotaevaporação e a enzima foi imobilizada na sequência. Os fosfolipídios dipalmitoil fosfatidil glicerol (DPPG) e palmitoil oleil fosfatidil glicerol (POPG) e a mistura dos dois foram utilizados neste trabalho nas proporções de (1:1) e (1:4) (m/m). Para construir um biossensor de dopamina baseado em monoamina oxidase b, filmes finos foram montados de poli (etilenoimina) PEI juntamente com a enzima Monoamina oxidase b (MAO-b) imobilizada ou não em lipossomos e depositados sobre eletrodo de ITO, tendo como mediador de elétrons o Azul da Prússia. Os filmes obtidos foram caracterizados por espectroscopias de fluorescência, UV-visível e dicroísmo circular. Os resultados indicaram que o filme é depositado com sucesso sobre quartzo e ITO. As medidas amperométricas foram realizadas nos filmes para detectar sensibilidades e limite de detecção e verificar qual arquitetura é mais adequada para a melhor composição do biossensor. Os resultados obtidos mostram que os lipossomos conservam a estrutura conformacional da enzima e os filmes compostos por PEI/MAO-B+POPG:DPPG na proporção (1:4) (m/m) indicam um melhor desempenho do biossensor, devido ao valor de sensibilidade encontrado de 0,33±0,02 ?A.cm- 2mM-1 e uma boa seletividade.

The barrier properties and long term strength retention of polymers are of significant importance in a number of applications. Enhanced lifetime food packaging, substrates for OLED based flexible displays and long duration scientific balloons are among them. Higher material requirements in these applications drive the need for an accurate measurement system. Therefore, a new system was engineered with enhanced sensitivity and accuracy. Permeability of polymers is affected by permeant solubility and diffusion. One effort to decrease diffusion rates is via increasing the transport path length. We explore this through dispersion of layered silicates into polymers. Layered silicates with effective aspect ratio of 1000:1 have shown promise in improving the barrier and mechanical properties of polymers. The surface of these inorganic silicates was modified with surfactants to improve the interaction with organic polymers. The micro and nanoscale dispersion of the layered silicates was probed using optical and transmission microscopy as well as x-ray diffraction. Thermal transitions were analyzed using differential scanning calorimetry. Mechanical and permeability measurements were correlated to the dispersion and increased density. The essential structure-property relationships were established by comparing semicrystalline and amorphous polymers. Semicrystalline polymers selected were nylon-6 and polyethylene terephthalate. The amorphous polymer was polyethylene terphthalate-glycol. Densification due to the layered silicate in both semicrystalline and amorphous polymers was associated with significant impact on barrier and long term creep behavior. The inferences were confirmed by investigating a semi-crystalline polymer - polyethylene - above and below the glass transition. The results show that the layered silicate influences the amorphous segments in polymers and barrier properties are affected by synergistic influences of densification and uniform dispersion of the layered silicates.

The development of techniques for colloidal nanoparticle synthesis has allowed scientists to fabricate materials that can manipulate light on a scale that is small even compared to the wavelength of the light itself. This ability has led to the development of myriad and diverse applications of nanostructures in wide-ranging fields. This thesis focuses on the investigation and exploitation of nanoscale material properties in the fields of medicine and energy. The unique optical properties of nanoparticles arise from their size and their high surface area to volume ratios compared to bulk materials. As a result of this relationship, the surface characteristics of nanoparticles generally dominate their properties, whereas in bulk materials the surface atoms have very little bearing on the properties of the composite. Chapter 1 gives an introduction to nanoparticles and their optical properties, including a discussion of the plasmon resonance and the properties imbued upon nanoparticles possesing such a resonance as well as the applicability of these properties that will be explored in the subsequent chapters. Chapter 2 presents a study of the interaction of cationic, hydrophobic gold nanoparticles as probes to elucidate specific regions of interest on cell surfaces. The high imaging contrast of gold nanoparticles in electron microscopy allows for visual, macroscopic observation of the aggregation patterns formed by these nanoparticles on cell surfaces. Plasmon resonant coupling between proximal nanoparticles is exploited in order to monitor nanoprobe binding and localization over time with the use of extinction spectroscopy. The role of surface proteins in the nanoparticle-cell surface interaction is elucidated, generating composite data with relevance in pharmaceutical development and pharmacokinetics. Additionally, bacteria strain-dependent toxicity is observed and subsequently investigated for smaller gold nanoparticle probes, demonstrating a potential use for nanoparticles as strain-specific antibiotics. The development of affordable, effective antibiotic technology is one of the major scientific challenges of our time; infections from pathogen-infested drinking water alone account for millions of deaths each year worldwide. In Chapter 3, we investigate the use of titanium dioxide as an inexpensive method to harness solar energy to split water into reactive species and thereby decontamitate solutions of E. coli. Though titanium dioxide is an excellent catalyst for water splitting, it requires UV irradiation, which is fairly lacking in the solar emission spectrum. Further, recuperation of titanium dioxide nanoparticles from solution is non-trivial, and its immobilization into a film greatly limits its surface area and charge carrier efficiency, thereby limiting its activity. We treat both the poor visible light absorption capability as well as the surface area limitation in this study. CdS semiconductor nanocrystals are used to extend the absorption edge of TiO₂ further into the visible light region of the spectrum by providing for lower-energy photon absorption and charge injection into titanium dioxide. TiO₂ is also electrochemically anodized to generate TiO₂ nanotube arrays, which have greatly increased surface area as well as more efficient charge transfer properties compared to thin films of TiO₂ nanoparticles. The utility of nanoparticles in increasing the light absorption of other systems continues as a theme in the work presented in the next two chapters. Chapter 4 ex- amines the plasmonic enhancement of the solar energy conversion in a biomimetic system. In this endeavor, we enhance the photocurrent generated by a light-transducing, proton-pumping protein, bacteriorhodopsin, in a 3-dimensional wet electrochemical cell. First, we increase the overall charge carrier separation with the use of a proton- selective membrane in order to minimize ionic depolarization in the cell. We then use plasmonic nanoparticles to exploit an irregularity in the bacteriorhodopsin photocycle known as the blue light effect. This effect shortens the timescale of the photocyle by more than 99% via blue photon absorption, but it has a very low natural occurrence. Plasmonic nanoparticles tuned to the blue wavelength region increase the flux of blue photons on a local level and thereby increase the overall photocurrent generation. We first examine the importance of nanoparticle field strength to photocurrent enhancement using silver nanospheres with different capping shell thicknesses. We then consider the trade-off between (1) using a nanoparticle with a plasmon resonance tuned perfectly to the blue wavelength region and (2) using a nanoparticle with a stronger field intensity but weaker energetic presence in the blue. By minimizing ionic depolarization, minimizing shielding of the plasmon electromagnetic field, and maximizing the field strength while maintaining the plasmon frequency at the proper wavelength, we demonstrate an enhancement of 5,000-fold in the photocurrent production by bacteriorhodopsin. Chapter 5 explores a variation on the theme of Chapter 4 with an application in cancer therapeutics. Here, a photodynamic cancer drug, protoporphyrin IX (PpIX), is incorporated into complexes with silver nanospheres, gold nanospheres, and gold nanorods. Each of these nanoparticles displays a plasmon resonance in a different region of the spectrum, with consequent different overlap with the absorption or emission of the drug. Photodynamic therapeutic potential is measured in situ and in vivo, and the drug activity is shown to be strongest when drug absorption overlaps with plasmon resonance. Absorption by electronic excitations in the particle crystal lattice is shown to function as a competitive light filter and decrease drug activity. Additionally, the method of attachment of the drug to the nanoparticle is examined. Maximum enhancement of drug activity is shown to require the drug to remain bound close to the nanoparticle surface, where the electromagnetic field strength is highest. This plasmonic enhancement effect on drug activity is shown to outstrip the increase in drug activity seen when using the nanoparticle solely as a delivery platform. In Chapter 6, some synthetic techniques are presented for various nanomaterials. Included are syntheses for gold, silver, and semiconductor nanoparticles of a variety of shapes and sizes as well as for TiO₂ nanotube arrays. The relationship of the ratio of capping agent to metal salt is explored for gold nanospheres, and a method for facile tuning of the longitudinal plasmon resonance displayed by gold nanorods is presented. Synthetic techniques are also presented for the nanoparticles whose applications are explored in the preceding chapters.

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Nanoscale visualisation of live cells and cellular components under physiological conditions has long been a goal in microscopy. The objective of this study was to validate the use of Atomic Force Microscopy (AFM) as a new tool in unravelling the mysteries of antimicrobial peptide mechanism of action. Using the simplest AFM imaging technique, we were able to analyse the influence of haemolytic melittin and anti-bacterial magainin 2 on different target membranes at nanometer resolution, without using fixing agents. First, magainin 2 was synthesised and purified by gel permeation chromatography and high performance liquid chromatography (HPLC). The purity of magainin 2 and melittin, isolated from bee venom (Sigma-Aldrich), was verified with electro spray ionisation mass spectrometry (ESI-MS). Second, dose-response experiments were used to determine the optimum peptide/target cell ratio that would allow interaction with the membrane without causing lysis. Third, peptide/target-cell samples were placed on silica plates and visualised using contact mode AFM. Images obtained of the cells before and after peptide treatment, showed distinct changes in cell membrane surface topology. We observed grooves, lesions, membrane collapse and vesiculation depending on the concentration, type of peptide and target-cell used, allowing us to make conclusions regarding the mechanism of action of melittin and magainin 2. In comparison with model membrane studies, our AFM results show that a peptide can function by more than one mechanism of action depending on the structural composition of the membrane, which appears to have specific segregated lateral organisation. Magainin 2 (non-toxic) selectively targets cell membranes using different mechanisms of action. In this way it can lyse bacterial membranes (anti-bacterial agent) using one mechanism, while using another mechanism to interact with mammalian cells at physiological concentrations, without destroying them. In contrast, melittin (toxic) is non-selective, and uses the same mechanism of interaction with bacterial and mammalian cells. In conclusion, we propose a new holistic model for the mechanism of action of antimicrobial peptides. / AFRIKAANSE OPSOMMING: Nanoskaal visualiseering van lewende selle en sellulêre komponente onder fisiologiese toestande is al 'n geruime tyd 'n mikpunt in mikroskopie. Die doel van hierdie studie was om antimikrobiese peptiede se meganisme van werking op teikenselle op nanoskaalvlak met AFM te visualiseer. Sonder om fikseermiddels by te voeg, het ons die eenvoudigste AFM tegniek gebruik om die effek van hemolitiese melittien en anti-bakteriële magainin 2 op verskillende teikenselle, in nanometer resolusie, waar te neem. Eerstens is Magainin 2 gesintesiseer en gesuiwer met behulp van gelpermeasie chromatografie en hoë doeltreffenheid vloeistof chromatografie (HPLC). Die suiwerheid van magainin 2 en kommersiële bye gif melittien, is bevestig met behulp van elektrosproei-ionisasie massaspektrometrie (ESI-MS). Tweedens, is dosis-respons eksperimente gebruik om die optimale peptied/teikensel verhouding te bepaal voordat membraanliese plaasvind. Derdens, is peptied/teikensel monsters op silika plate gevisualiseer met gebruik van kontak AFM. Die beelde van die selle, voor en na peptied behandeling, het duidelike veranderinge in seltopologie getoon. Ons het groewe, letsels, membraaninstorting en vesikulasie, afhangende van die konsentrasie peptied en teikensel gebruik, waargeneem. Dit het ons toegelaat om tot gevolgtrekkings te kom aangaande die meganisme van werking van melittien en magainin 2. In ooreenstemming met model membraan studies, het ons AFM resultate gewys dat 'n peptied veelvoudige meganismes van werking kan hê, afhangend van die strukturele samestelling van die membraan, wat klaarblyklik laterale segregasie toon. Magainin 2 (nie-giftig) is selektief ten opsigte van teikenselle omdat dit gebruik maak van verskillende meganismes van werking op bakteriële en soogdier selle. In teenstelling is melittien (giftig) nie-selektief, en gebruik dieselfde meganisme van werking op bakteriële en soogdierselle. Ten slotte, stel ons 'n nuwe model vir die meganisme van werking voor.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / Please refer to full text to view abstract

Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / Synthesis and structural characterization of two novel cationic and three new neutral reversible addition–fragmentation chain transfer (RAFT) agents is described. The cationic RAFT agents bear a quaternary ammonium group: N,N-dimethyl-N-(4- (((phenylcarbonothionyl)thio)methyl)benzyl)ethanammonium bromide (PCDBAB) and N-(4-((((dodecylthio)carbonothioyl)thio)methyl)benzyl)-N,N-dimethylethanammonium bromide (DCTBAB). The three neutral RAFT agents synthesized are 1,4- phenylenebis(methylene)dibenzene carbodithioate (PCDBDCP), didodecyl-1,4- phenylenebis(methyllene)bistrithiocarbonate (DCTBTCD) and 11-(((benzylthio)carbonothioyl) thio)undecanoic acid (BCTUA). The self-assembly behaviour in diluted aqueous solutions of the cationic RAFT agents, PCDBAB and DCTBAB, is described. The self-assembly behaviour was promoted by the presence of the thiocarbonyl- thio group on the RAFT agents, in addition to the overall chemical structure of the surfactant that also influence self-assembly. The RAFT agents were used for the bulk or miniemulsion RAFT-mediated controlled free-radical polymerization in the presence of clay to yield polymer–clay nanocomposites (PCNs). Bulk polymerization resulted in PCNs with better control of molar mass and polydispersity index (PDI) values when compared to PCNs prepared by miniemulsion polymerization. In both bulk and miniemulsion polymerizations the molar masses and PDI values were dependent on the amount of clay and RAFT agent present in the system. Free-radical bulk neutral RAFT agent-mediated polymerization resulted in PCNs with predominantly intercalated morphology. This was attributed to radical–radical coupling of the initiator anchored onto the clay galleries on which polymerization took place. On the other hand, when the cationic RAFT agent anchored onto clay, i.e. RAFT-modified clay was used, bulk polymerization resulted in predominantly exfoliated PCNs. However, miniemulsion polymerization carried out in the presence of the RAFT-modified clays resulted in PCNs with a morphology that ranged from partially exfoliated to intercalated morphology, as the clay loading was increased. The changing morphology for miniemulsion-based PCNs was attributed to the decreasing molar mass as the clay loading was increased. The PCNs obtained had enhanced thermo-mechanical properties as a result of the presence of clay. The thermo-mechanical properties depended on the molar mass, PDI, clay loading, and the morphology of the PCNs.

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.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Solution electrospinning is a technique used to produce polymer micro- or nanofibres. Recently a great deal of research has been done on the application of polymer nanofibres produced by this method. The solution electrospinning of polyolefins have not been researched in-depth mainly due to the difficulty in dissolving these polymers in suitable electrospinning solvents. We managed to electrospin polypropylene copolymers at room temperature, obtaining both polymer micro- and nanofibres. A suitable solvent system was developed (cyclohexane/DMF/acetone) that allowed for the room temperature solution electrospinning of these crystalline polypropylene copolymers. It was also shown that using propylene-1-alkene copolymers with a low comonomer content was a facile way of producing crystalline polyolefins nano – and microfibers. Similar attempts to electrospin isotactic polypropylene were unsuccessful, even though lower molecular weight materials were used than in the case of the copolymers. This lead to an investigation of solution melting temperature by SCALLS. The copolymers showed great variance in their solution melting temperatures despite the fact that they all had more or less the same crystallinity and amount of comonomer, indicating that the type of comonomer played an important role in the solubility of the copolymer. The effect of different collectors was investigated, but in the end it was found that between spinning unto ice, foil on ice of just foil, foil still seemed to be the best collector. Comparing crystallinity of the polymer powders with that of the polymer fibres by DSC and WAXD, it was found that there is a difference in the crystallinity of the fibres and the powders. EVOH is a polymer with excellent properties and electropspinning of this polymer is relatively easy due to the fact that it dissolves quite easily in conductive solvents. DMF, Isopropanol/water and DMSO were all tested as suitable solvents and the morphology was compared through the use of SEM. The morphology of the fibres indicated that DMSO was the best solvent. The influence of the spinning parameters was determined for both systems of DMF and DMSO. These nanofibres were used as reinforcement in LDPE matrix and the mechanical properties of the LDPE matrix was improved with the addition of both aligned and unaligned fibres. The next step was the electrospinning of EVOH fibres containing MWCNT. TEM, FE-SEM and TGA were used to confirm the presence of the MWCNT as well as determine the distribution of the MWCNT inside the nanofibres. The nanotubes were distributed through the fibres; however agglomeration of the nanotubes did still take place. The nanofibres containing MWCNT were also used to make composites where the fibres were melted, leaving the MWCNT behind in the polymer matrix. This was done in both LDPE and EVOH matrices. The LDPE/MWCNT composites did not give positive results, on the other hand the EVOH/MWCNT composite showed an improvement in the mechanical properties compared to pure EVOH. The attachment of fluorescent dye molecules to the surface of the MWCNT was attempted and through fluorescent microscopy and the dispersion of the nanotubes inside the fibres as well as the composite could be seen. This study proved that polyolefin nanofibres could be obtained, giving rise to more applications for these versatile polymers. It also confirmed the importance of nanofibres as reinforcement and the use of nanofibres as a way to incorporate MWCNT in a polymer matrix. / AFRIKAANSE OPSOMMING: Elektrospin in ‘n oplosmiddel is ‘n tegniek wat gebruik word om polimeer mikro- en nanovesels te produseer. Die afgelope tyd word baie navorsing gedoen oor die aanwending van polimeer nanovesels wat geproduseer word op hierdie manier. Daar is nog min navorsing gepubliseer wat handel oor die elektrospin van poliolefiene uit ‘n oplosmiddel, deels oor hoe moeilik dit is om ‘n geskikte elektrospin oplosmiddel te vind vir hierdie polimere. In hierdie studie het ons mikro- en nanovesels verkry deur polipropileen kopolimere te elektrospin by kamertemperatuur. Die polimere is opgelos in ‘n oplosmiddel sisteem wat bestaan uit sikloheksaan/dimetielformamied/asetoon, by hoë temperatuur en het toegelaat dat die polimere in oplossing bly by kamertemperatuur. Hierdie diverse kopolimere het verskillende resultate gegee, sommige polimere het mikrovesels produseer, waar ander nanovesels geproduseer het. Die vessel morfologie is ondersoek deur die gebruik van Skandering Elektron Mikroskopie (SEM) en daar is gevind dat die vesels nie ‘n gladde voorkoms het nie, maar dat daar kraalvormige morfologie gesien kon word. Om dit te voorkom is sout by die oplosmiddel sisteem gevoeg. Die invloed van die verskillende parameters op die vesels se deursnit is ondersoek vir al die kopolimere. Die byvoeging van sout het gelei tot ‘n meer gladde vesel morfologie. Die effek van die gebruik van verskillende oppervlaktes om die vesels op te vang is ondersoek en die die kristalliniteit van die polimeer poeiers is vergelyk met die kristalliniteit van die polimeer vesels met die hulp van DSC en WAXD. ‘n Poging is aangewend om isotaktiese polipropileen te elektrospin uit oplossing, maar ons kon nie daarin slag om die polimeer op te los nie, al was die molekulêre gewig minder as die van die kopolimere. Dit het gelei tot die ondersoek van die smeltpunt temperatuur in oplossing deur die gebruik van oplossing kristallisasie-analise deur laser lig verstrooing (SCALLS). Al die kopolimere het min of meer dieselfde kristalliniteit en hoeveelheid komonomer bevat, tog het hulle smeltpunt temperatuur in oplossing baie verskil. Dit het gedui op die feit dat die tipe komonomeer ‘n groot rol speel in die oplosbaarheid van die kopolimeer. Die elektrospin van etileen-ko-vinielalkohol (EVOH) is ook ondersoek. DMF, Isopropanol/Water en Dimetielsulfoksied (DMSO) is getoets as geskikte oplosmiddels en die morfologie van die vesels is vergelyk deur die gebruk van SEM. Die tyd wat die polimeer in oplossing gebly het asook die morfologie van die vesels, het aangedui dat DMSO die mees geskikte oplosmiddel was. Die invloed van die elektrospin parameters was vasgestel vir beide DMF en DMSO sisteme. Hierdie nanovesels is gebruik as versterking in ‘n LDPE matriks en die meganiese eienskappe van die LDPE matriks is verbeter deur die toevoeging van beide nie-geweefde en gerigte veselsopppervlakte. Die volgende stap was die elektrospin van EVOH vesels wat multi-ommuurde koolstof nanobuisies (MWCNT) bevat. TEM, FE-SEM en TGA was gebruik om te bevestig dat die vesels wel MWCNT bevat asook om die verspreiding van MWCNT in die vesels aan te dui. Die nanobuisies was versprei deur die vesels, maar bundels nanobuisies het tog voorkom in sommige plekke. Die nanovesels wat MWCNT bevat is ook gebruik om nanosamestellings te maak, waar die vesels gesmelt is om net MWCNT agter te laat in die polimeer matriks. Hierdie was gedoen in beide LDPE en EVOH matrikse. Geen positiewe resultate is verkry vir die LDPE/MWCNT nanosamestelling nie, maar die EVOH/MWCNT nanosamestelling het aan die anderkant ‘n groot verbetering getoon in die meganiese eienskappe in vergelyking met EVOH sonder MWCNT. ‘n Poging was aangewend om fluoreseerende molekules aan die oppervlak van MWCNT te voeg en deur fluoresensie mikroskopie kon die verspreiding van die MWCNT in die vesels asook in die nanosamestellings gesien word. Hierdie studie het bewys dat poliolefien nanovesels gemaak kan word wat lei tot die aanwending van hierdie polimere in nog meer toepassings. Dit het ook die belangrikheid van die gebruik van nanovesels as versterking in nanosamestellings bevestig asook die gebruik van nanovesels as ‘n manier om MWCNT in ‘n matriks te plaas.