Philosophiae Doctor - PhD / The development of finely dispersed powders and superfine-grained materials intended for application in various areas of science and engineering is one of the challenges facing modern nanotechnology. Thus, specific fundamental and applied research was required in order to consolidate advancement made in preparing nano- and submicron crystalline composite materials. Useful templates for electrochemical deposition of nanowires include porous alumina films formed by anodic oxidation of aluminium, nuclear track-etched porous membranes, nanochannel array-glass and mesoporous channel hosts. The properties of the nanowires are directly related to the properties of the nanoporous templates such as, the relative pore orientations in the assembly, the pore size distribution, and the surface roughness of the pores. The template synthesis method, based on the use of porous polymeric and inorganic matrixes, is now actively used for synthesis of such composite materials. The method allows the chemical and/or electrochemical synthesis of nano- and microstructured tubes and wires consisting of conducting polymers, metals and semiconductors.In this study various technological challenges relating to template synthesis and development of nickel nano- and microstructures on adequately strong and durable substrates were investigated. The two methods used were the electrochemical and chemical deposition. “Hard nickel” bath solution was used for optimal nickel deposition. This optimization included investigating variables such as the template structure, type of electrolyte and form of electrolytic deposition. Scanning Electron Microscopy was used to investigate the structures of template matrixes and the resultant materials. The cyclic voltammetry method was applied for the analysis of electrochemical properties and hydrogen evaluation reaction of nano- and microstructured nickel based electrodes. The activity of composite nano- and microstructured materials in various configurations resulting from pore filling of template matrices by nickel was explored. Studies of the physical structure and chemical properties of the nanostructured materials included investigating the necessary parameters of template matrices. The optimum conditions of synthesis, which allowed development of materials with the highest catalytic activity, were determined.  The effect of the template structure on microcrystallinity of the catalyst particles was established using the XRD method. Different new types of non-commercial asymmetric ion track membranes has been tested for nanostructure preparation. The catalytic activity of the new developed nanomaterials is higher as compared to materials using commercial templates. The procedures to modify the newly developed nickel catalyst with Pt, Pd and Pt-Pd alloy have been developed. The Pt and Pt-Pd alloy containing catalyst showed the best performance in water electrolysis. In this work, the promising role for specific application of the new materials in hydrogen economy has been demonstrated. / South Africa

The study of the nanotechnology system in South Africa is an analysis of the South African nanotechnology innovation system, with a discussion of background information regarding nanotechnology awareness, involvement, funding, personnel, education, networking and equipment, and illustration of the level of nanotechnology activities for each product life cycle and per institution. The document contains a classification of nanotechnology industries regarding time to market, market potential, disruptiveness and complexity, identifies innovation hampers for the South African nanotechnology community and ranks nanotechnology national and international nanotechnology buyers, suppliers, competitors and relationships. Lastly, innovative strategies are formulated from information gathered on internal South African nanotechnology strengths and weaknesses, and external nanotechnology opportunities and threats. / Dissertation (MEng)--University of Pretoria, 2010. / Graduate School of Technology Management (GSTM) / Unrestricted

Symmetry in photonic crystals is reflected in the structure of their photonic bands and symmetry breaking can result in the development of complete photonic band gaps, leading to enhanced optical properties. This can be difficult for self-assembled nanostructures, due to their restriction by fundamental principles to preferential geometries, but can be achieved through the application of external stimuli. In order to explore such an approach, elastomeric, nanoengineered, polymer photonic crystal structures have been fabricated on a large scale, through a method of shear induced self-assembly of 200nm monodisperse, polymer spheres with a core-shell structure. Determination of the assembly geometry through light diffraction experiments reveals a highly symmetric structure of close-packed, core-shell particles, with its orientation governed by the directionality imposed by the fabrication procedure. In these tuneable photonic crystals, application of external strain at directions of different crystallographic symmetry, accompanied by synchronised optomechanical measurements, reveals strong anisotropic optomechanical properties. It is shown that mechanical properties are primarily dominated by the viscoelastic nature of the shell material, while the strain-induced symmetry breaking reveals previously forbidden resonant peaks. Experiments involving uniaxial extension at principal and non-principal directions verify the underlying symmetry of the crystal lattice and consistently reproduce the anisotropic optical properties, providing information regarding the dual microstructure that controls the optomechanical response of these systems. Simulations based on a model of close-packed hard spheres predict the appearance of secondary resonances and suggest a structural transition from an fcc to a lower symmetry monoclinic crystal lattice. A more elaborate micromechanical model does not verify this transition but predicts the strain dependence of dominant spectroscopic peaks. Experiments involving different crosslinking densities reveal individual contributions from the elements comprising the material's dual microstructure. The inherently low refractive index contrast featured by these polymeric systems forbids the development of full photonic band gaps but symmetry based principles can be applicable to other structures with similar topological restrictions. Results provide a possible route for fabrication of active deformable nanostructures and aid our understanding of self-assembly in these complex systems, leading to optimised large-scale fabrication.

Platinum catalysts are prepared on highly ordered pyrolytic graphite (HOPG). Two different methods are used to deposit platinum onto HOPG; electrochemical deposition and impregnation followed by thermal decomposition. To increase interactions between the Pt deposits and the carbon support, HOPG is oxidized either electrochemically or with ozone gas. The combination two different deposition techniques and three different substrates (freshly cleaved, electrochemically, and ozone oxidized HOPG) results in six different Pt/carbon electrodes that are studied with respect to their particle morphology, activity towards electrochemically oxidizing adsorbed carbon monoxide (COads), and electrochemical stability. Oxidation of HOPG generated pits on the basal plane; ozone oxidation formed nano-pits, < 10 nm in diameter; electrochemical oxidation produced larger pits, > 85 nm in diameter. Regardless of the substrate pre-treatment, electrochemical deposition resulted in clusters of nanoparticles, while impregnation followed by thermal decomposition resulted in individual Pt nano-catalysts. Regardless of the deposition technique, Pt particles are confined to step edges on freshly cleaved HOPG, and dispersed over the basal plane on oxidized HOPG. When comparing all six electrodes it became evident that substrate pre-treatment did not affect the electrochemical activity of the electrodes towards the oxidation of COads, while the method of Pt deposition did significantly affect the measured activity. For example, Pt/HOPG electrodes prepared by electrochemical deposition using short deposition times, < 10 s, show slower COads electro-oxidation kinetics compared to polycrystalline Pt foil, while electrodes prepared by impregnation followed by thermal decomposition show faster kinetics compared to polycrystalline Pt foil. For a given substrate, Pt/HOPG electrodes prepared by impregnation followed by thermal decomposition proved to be more electrochemically stable than electrodes prepared by electrochemical deposition. For a given deposition technique, ozone oxidized HOPG has the greatest stabilizing effect. The chemical interaction between the Pt catalyst and the carbon substrate was studied by XPS analysis. It was found that Pt 4f spectra of all six Pt/HOPG electrodes were shifted to higher binding energies indicating that Pt was interacting with the HOPG possibly forming Pt-C bonds. The XPS results indicate that the electrochemical stability is positively influenced by the interaction between the catalyst and the carbon support.

Rapid and sensitive detection of biomolecules is an important issue in nanomedicine. Many disorders are manifested by changes in protein levels of serum and other biofluids. Rapid and effective differentiation between normal and cancerous cells is an important challenge for the diagnosis and treatment of tumor. Likewise, rapid and effective identification of pathogens is a key target in both biomedical and environmental monitoring. Most biological recognition processes occur via specific interactions. Gold nanoparticles (AuNP s) feature sizes commensurate with biomacromolecules, coupled with useful physical and optical properties. A key issue in the use of nanomaterials is controlling the interfacial interactions of these complex systems. Modulation of these physicochemical properties can be readily achieved by engineering nanoparticles surface. Inspired by the idea of mimicking nature, a convenient, precise and rapid method for sensing proteins, cancerous cells and bacteria has been developed by overtaking the superb performance of biological olfactory systems in odor detection, identification, tracking, and location. On the fundamental side, an array-based/‘chemical nose’ sensor composed of cationic functionalized AuNPs as receptors and anionic fluorescent conjugated polymers or green fluorescent proteins or enzyme/substrates as transducers that can properly detect and identify proteins, bacteria, and cancerous cells has been successfully fabricated.

Particles can be adsorbed to liquid-fluid interface to minimize interfacial energy. The adsorbed particles interact in many ways. There has been a lot of theoretical predictions as well as experimental measurements of the interaction potential between particles confined at interfaces. Experimentally, we track multiple particles using optical microscope image processing of isolated pairs of particles and of more concentrated systems. Statistical methods were implemented to compute microparticle interaction forces from tracking data. The accuracy of different methods were tested with Monte Carlo simulation, which showed that care is needed to avoid artifacts. Our measurements confirmed the absence of significant pair-interactions among charged microparticles and liquid droplets at flat air-water interfaces. At the interface between water and a fluorocarbon, however, we observed strong interactions that cannot be explained by capillary interactions among neutral particles. Theoretically, we focused on the capillary interaction mediated by the curvature of interface. The perturbation to a cylindrical interface upon adsorption of a single spherical particle is studied first. We present an analytical model of the interfacial shape and energy upon adsorption of a single particle, and then calculate the interaction between two particles. Based on our result for a cylindrical interface, we propose a general formula for the force on a particle on a curved interface having constant mean curvature (i.e., not subject to an external forces). This study provides an important step toward understanding the interactions among interfacial particles.

Porous metal oxide materials, particularly those comprised of silica or titania, find use in many applications such as low-k dielectric materials for microelectronics as well as chemical sensors, micro/nanofluidic devices, and catalyst substrates. For this dissertation, the focus will be on the processing of porous metal oxide materials covering two subjects: hierarchical porosity exhibited over two discrete length scales and incorporation of functional nanomaterials. To generate the porous silica materials, the technique of supercritical carbon dioxide infusion (scCO2) processing was heavily relied upon. Briefly, the scCO2 infusion processing utilizes phase selective chemistries within a pre-organized amphiphilic block copolymer template using scCO2 as the reaction medium to selectively hydrolyze and condense silica precursors to yield mesoporous materials. To further develop the scCO 2 infusion processing technique, hierarchically porous silica materials were generated on unique substrates. Hierarchically structured silica nanochannels were created using a combination of scCO2 infusion processing and nanoimprint lithography (NIL) patterned sacrificial polymer templates to yield mesopores and airgap structures respectively. Hierarchically porous silica materials were also generated on alternative substrates, in the form of cellulose filter paper, which were used to host the amphiphilic block copolymer template to yield tri-modal porosity silica materials. To extend the applicability of mesoporous silica generated from scCO 2 infusion processing, functional nanomaterials, in the form of pre-synthesized gold nanoparticles, fullerene derivatives, and polyhedral oligomeric silsequioxanes (POSS) were embedded within the mesoporous silica to produce unique composite materials. The functional nanomaterials were able to impart specific properties, typically only affored to the functional nanomaterials, upon the mesoporous silica thin film with an example being enhanced thermal and hydrothermal properties of mesoporous silica doped with POSS molecules. To continue research with functional nanomaterials, nanoparticle composite materials, comprised of crystalline metal oxide nanoparticles and binder/filler materials, either organic or inorganic, were also evaluated as novel NIL resist materials. Patterning of the nanoparticle composite materials, specifically, but not limited to, titanium dioxide based materials, into two dimensional, arbitrarily shaped, sub-micron features was readily achieved on either rigid or flexible substrates. True three-dimensional structures, based on nanoparticle composite materials, were fabricated by utilizing release layers and pre-patterned substrates.

Nanoparticles are regarded as exciting new building blocks for functional materials due to their fascinating physical properties because of the nano-confinement. Organizing nanoparticles into ordered hierarchical structures are highly desired for constructing novel optical and electrical artificial materials that are different from their isolated state or thermodynamics random ensembles. My research integrates the surface chemistry of nanoparticles, interfacial assembly and lithography techniques to construct nanoparticle based functional structures. We designed and synthesized tailor-made ligands for gold, semiconductor and magnetic nanoparticle, to modulate the assembly process and collective properties of the assembled structures, by controlling the key parameters such as particle-interface interaction, dielectric environments and inter-particle coupling etc. Top-down technologies such as micro contact printing, photolithography and nanoimprint lithography are used to guide the assembly into arbitrarily predesigned structures for potential device applications.

Developing effective biosensor for proteins, cells, and tissues would enhance the likelihood of early disease detection and treatment. Traditional specificity-based methods are limited by the requirement of prior knowledge of the specific biomarker(s) and high production cost. My research has been focused on developing a rapid and efficient biosensor based on selective interactions using an unbiased array of supramolecular complexes formed between cationic gold nanoparticles and fluorescent proteins. The sensor is capable of discriminating between mammalian cells, as well as healthy and metastatic tissues with significantly small amount of samples, an important requirement for disease diagnosis in clinics. In addition to the cell/tissue state classification, the sensor array is able to identify protein imbalances in undiluted serum, demonstrating the applicability of the sensor array in physiological matrices. Later, I have developed a triple-channel high-throughput sensor to identify chemotherapeutic drug mechanism that would simplify drug discovery. Overall, the sensor array provides a generic tool for bio-profiling, precluding additional processing steps prior to screening and holds great promise for personalized screening of disease states.

There is growing interest in the use of nanoemulsions as delivery systems for lipophilic functional agents in food and beverage products due to their high optical clarity, physical stability and bioavailability. The goal of this research is to establish quantitative structure-function relationships to allow rational formulation of food-grade nanoemulsions for food and beverage applications. Initially, formation of oil-in-water nanoemulsions using a low energy method was examined. Nanoemulsions were formed using the phase inversion temperature (PIT) method, which involves heating a surfactant, oil, water (SOW) systems near the PIT, and then cooling rapidly with stirring. Preliminary experiments were carried out using a model system consisting of a non-ionic surfactant (C12E4), hydrocarbon oil (tetradecane), and water. Nanoemulsions were formed by holding SOW mixtures near their PIT (38.5 °C) and then cooling them rapidly to 10 °C. The PIT was measured using electrical, conductivity and turbidity methods. The optimum storage temperature for PIT-nanoemulsions was about 27 °C lower than the PIT. The stability of PIT-nanoemulsions at ambient temperatures can be improved by adding either Tween 80 (0.2 wt%) or SDS (0.1 wt%) to displace the C12E4 (Brij 30) from the nano-droplet surfaces. Experiments were then carried out to establish if stable nanoemulsions could be formed using the PIT method from food-grade ingredients. Nanoemulsions were fabricated from a non-ionic surfactant (Tween 80) and flavor oil (lemon oil) by heat treatment. Different types of colloidal dispersion could be formed by simple heat treatment (90 °C, 30 minutes) depending on the surfactant-to-oil ratio (SOR): emulsions at SOR < 1; nanoemulsions at 1 < SOR < 2; microemulsions at SOR > 2. The results suggested that there was a kinetic energy barrier in the SOW system at ambient temperature that prevented it from moving from a highly unstable system into a nanoemulsion system. The conditions where stable nanoemulsions could be fabricated were also established when sucrose monopalmitate (SMP) and lemon oil were used as the surfactant and oil phase. Nanoemulsions (r < 100 nm) were formed at low surfactant-to-oil ratios (SOR < 1) depending on homogenization conditions, whereas microemulsions (r < 10 nm) were formed at higher ratios (SOR > 1). Relatively stable nanoemulsions could be formed at pH 6 and 7, but extensive particle growth/aggregation occurred at lower and higher pH values. Flavor oil nanoemulsions were also formed using an emulsion titration method that involves titration of emulsion droplets into surfactant micelle solutions. In this study, the effectiveness of nanoemulsion formation using nonionic surfactants (sucrose monopalmitate (SMP) and/or Tween 80 (T80) was investigated. Lemon oil was transferred from emulsion droplets into the micelle phase until a critical lemon oil concentration (Csat ) was reached. The solubilization process was rapid (< few minutes), with the rate increasing with increasing surfactant concentration. The value of Csat increased with increasing surfactant concentration and was higher for SMP than Tween 80. The influence of lemon oil composition (1×, 3×, 5×, and 10×) on the formation and properties of oil-in-water nanoemulsions was also studied. Initially, the composition, molecular characteristics, and physicochemical properties of four lemon oils were established. The main constituents in 1-fold lemon oil were monoterpenes (> 90 %), whereas the major constituents in 10-fold lemon oil were monoterpenes (≈ 35%), sesquiterpenes (≈ 14%) and oxygenates (≈ 33%). The density, interfacial tension, viscosity, and refractive index of the lemon oils increased as the oil fold increased ( i.e., 1× < 3× < 5× < 10×). The stability of oil-in-water nanoemulsions produced by high pressure homogenization was strongly influenced by lemon oil composition. The lower fold oils were highly unstable to droplet growth during storage (1×, 3×, 5×) with the growth rate increasing with increasing storage temperature and decreasing oil fold. Oil fold also affected the solubilization and stability of lemon oil nanoemulsions titrated into a non-ionic surfactant (Tween 80) solution. The movement of oil molecules from nanoemulsion droplets to surfactant micelles increased with increasing lemon oil fold. Finally, nanoemulsions were used as delivery systems for β-carotene, a bioactive lipophilic component. The influence of carrier oil composition (ratio of digestible to indigestible oil) on the physical stability, microstructure, and bioaccessibility of β-carotene nanoemulsions was investigated using a simulated gastrointestinal tract model. The extent of free fatty acid production in the small intestine increased as the amount of digestible oil in the droplets increased. The bioaccessibility of β-carotene also increased with increasing digestible oil content, ranging from ≈ 5% for the pure lemon oil system to ≈ 76% for the pure corn oil system.