Soot is formed whenever the combustion of hydrocarbon fuels is incomplete. Since soot particles are very small, they can be inhaled and cause severe health problems, such as pulmonary diseases. They can also cause environmental pollution, and have a significant effect on global warming and melting of polar ice sheets. The environmental and health impact of soot depends strongly on soot particle size and morphology, so there is a pressing need for measuring techniques that characterize aerosolized soot. Laser-Induced incandescence (LII) has proved to be a reliable technique for making spatial and temporal measurements of soot primary particle sizes and soot volume fractions. Nevertheless, there are some unresolved issues in LII, which may cause large errors in soot primary particle size inferred from LII data. One of these issues is anomalous cooling, which is the unexpectedly high initial rate of soot particle cooling observed in experiments, which can not be predicted by LII models. Among the speculations about the possible causes of this phenomenon is the transient gas dynamics effects which have been ignored in LII models. Another phenomena that has been speculated to affect LII predictions in high fluence LII, is how the gas dynamics of sublimed carbon clusters impact the local gas dynamics surrounding the particle during the cooling phase. The focus of this thesis is to investigate transient effects on heat conduction in low fluence LII, and the gas dynamics of sublimed species in high fluence LII using Direct Simulation Monte Carlo (DSMC) method. DSMC is a statistical/numerical method which works based on the physics of Boltzmann equation. In this method a large number of real molecules are represented by the so called simulated molecules and the state of these molecules is tracked during the simulation as they undergo collisions with each other and with the boundaries. The results show that transient effects contribute to anomalous cooling but are not the only cause of this phenomenon. The time scale over which transient effects are significant is also found to be very close to that of anomalous cooling which implies the real cause of anomalous cooling has some similarities to transient effects. Also regarding gas dynamics of sublimation, two effects in particular have been investigated using DSMC, namely, back flux of sublimed species and formation of shock waves. DSMC results confirm the back flux of sublimed species but no shock wave was observed for the boundary conditions considered in this study.

Abstract The properties of starch nanoparticles (SNPs) labeled with the fluorescent dye pyrene (Py-SNPs) were probed by using fluorescence quenching, pyrene excimer formation, and transmission electron microscopy (TEM). Pyrene labeling of the SNPs was achieved by reacting 1-pyrenebutyric acid with the hydroxyl groups of the SNPs under basic conditions and in the presence of diisopropylcarbodiimide. This procedure did not degrade the SNPs as confirmed by dynamic light scattering (DLS) and afforded a means to generate a pyrene labeling level ranging from 0.5 to 5.0 mol% of the glucose units making up the SNPs. A polymeric quencher was also synthesized to probe the accessibility of the interior of the Py-SNPs by using fluorescence quenching measurements. The polymeric quencher was a 2K poly(ethylene glycol) terminated at one end with a methyl group and a nitropropane group at the other. Unfortunately these quenching experiments were abandoned when it was found that the polymeric quencher synthesized for these experiments absorbed too strongly where pyrene absorbs. Intramolecular pyrene excimer formation in the Py-SNPs was investigated by steady-state and time-resolved fluorescence. These experiments demonstrated that the Py-SNPs contract but do not overlap like linear polymers do in the semi-dilute regime. They also showed that despite the inherent rigidity of starch, the Py-SNPs deformed in water to allow their hydrophobic pyrene labels to cluster toward the center of the SNPs to minimize pyrene-solvent contacts. This segregation of the hydrophobic pyrene labels led to a distinct core-shell structure for the Py-SNPs which was illustrated in TEM images acquired on films prepared with the Py-SNPs. In summary, this thesis has uncovered some unexpected properties of the SNPs. Their branched structure makes their interpenetration difficult in the semi-dilute regime which forces them to contract. SNPs are thus deformable and their deformation can be probed quantitatively by using fluorescence and TEM.

A multidisciplinary literature survey revealed that copolymeric nanoparticles could be applied in various technologies such as the production of paint, adhesives, packaging material and lately especially drug delivery systems. The specialized application and investigation of copolymers in drug delivery resulted in the synthesis of two series of copolymeric materials, i.e. poly(styrene-co-methyl methacrylate) (P(St-co-MMA)) and poly(styrene-co-ethyl methacrylate) (P(St-co-EMA)) were synthesized via the technique of o/w microemulsion copolymerization. These copolymers have not as yet been utilized to their full potential in the development of new drug delivery systems. However the corresponding hydrophobic homopolymer poly(styrene) (PS) and the hydrophilic homopolymer poly(methyl methacrylate) (PMMA) are known to be biocompatible. Blending of homopolymers could result in novel applications, however is virtually impossible due to their unfavorable mixing entropies. The immiscibility challenge was overcome by the synthesis of copolymers that combined the properties of the immiscible homopolymers. The synthesized particles were analyzed by gel permeation chromatography combined with multi-angle laser light scattering (GPC-MALLS) and attenuated total reflectance Fourier infrared spectroscopy (ATR-FTIR). These characterizations revealed crucial information to better understand the synthesis process and particle properties i.e. molecular weight, nanoparticle size and chemical composition of the materials. Additionally, GPC-MALLS revealed the copolymer chain conformation. These characterizations ultimately guided the selection of appropriate copolymer nanoparticles to develop a controlled-release drug delivery system. The selected copolymers were dissolved in a pharmaceutically acceptable solvent, tetrahydrofuran (THF) together with a drug, rifampin. Solvent casting of this dispersion resulted in the evaporation of the solvent and assembly of numerous microscale copolymer capsules. The rifampin molecules were captured in these microcapsules through a process of phase separation and coacervation. These microcapsules finally sintered to produce a multi-layer film with an unusual honeycomb structure, bridging yet another size scale hierarchy. Characterization of these delivery systems revealed that both series of copolymer materials produced films capable of controlling drug release and that could also potentially prevent biofilm adhesion. / Thesis (Ph.D. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2008.

A multidisciplinary literature survey revealed that copolymeric nanoparticles could be applied in various technologies such as the production of paint, adhesives, packaging material and lately especially drug delivery systems. The specialized application and investigation of copolymers in drug delivery resulted in the synthesis of two series of copolymeric materials, i.e. poly(styrene-co-methyl methacrylate) (P(St-co-MMA)) and poly(styrene-co-ethyl methacrylate) (P(St-co-EMA)) were synthesized via the technique of o/w microemulsion copolymerization. These copolymers have not as yet been utilized to their full potential in the development of new drug delivery systems. However the corresponding hydrophobic homopolymer poly(styrene) (PS) and the hydrophilic homopolymer poly(methyl methacrylate) (PMMA) are known to be biocompatible. Blending of homopolymers could result in novel applications, however is virtually impossible due to their unfavorable mixing entropies. The immiscibility challenge was overcome by the synthesis of copolymers that combined the properties of the immiscible homopolymers. The synthesized particles were analyzed by gel permeation chromatography combined with multi-angle laser light scattering (GPC-MALLS) and attenuated total reflectance Fourier infrared spectroscopy (ATR-FTIR). These characterizations revealed crucial information to better understand the synthesis process and particle properties i.e. molecular weight, nanoparticle size and chemical composition of the materials. Additionally, GPC-MALLS revealed the copolymer chain conformation. These characterizations ultimately guided the selection of appropriate copolymer nanoparticles to develop a controlled-release drug delivery system. The selected copolymers were dissolved in a pharmaceutically acceptable solvent, tetrahydrofuran (THF) together with a drug, rifampin. Solvent casting of this dispersion resulted in the evaporation of the solvent and assembly of numerous microscale copolymer capsules. The rifampin molecules were captured in these microcapsules through a process of phase separation and coacervation. These microcapsules finally sintered to produce a multi-layer film with an unusual honeycomb structure, bridging yet another size scale hierarchy. Characterization of these delivery systems revealed that both series of copolymer materials produced films capable of controlling drug release and that could also potentially prevent biofilm adhesion. / Thesis (Ph.D. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2008.

A multidisciplinary approach has been applied to the development of sustainable technologies for three industrially relevant projects. Reversible ionic liquids are novel carbon dioxide capture solvents. These non-aqueous silylamines efficiently capture carbon dioxide through chemical and physical absorption and release carbon dioxide with minimal addition of heat. The development of these capture agents aims to eliminate the need for a co-solvent, while minimizing energy loss and achieving solvent recyclability. Also presented is the use of carbon dioxide for amine protection during chemical syntheses. Amine protection is widely used in almost all sectors of chemical and pharmaceutical industries. The use of carbon dioxide as a reversible protecting group reduces solvent waste during protection and deprotection and improves the atom economy of existing processes. Sustainable chemistry has also been applied to the use of reversible ionic liquids as switchable surfactants for nanoparticle synthesis. The reversible ionic liquid system offers two significant advantages toward a more efficient synthesis and deposition of nanoparticles in that an additional surfactant is not required, and due to the reversible nature of the ionic liquids, a facile and waste-reduced deposition method exists.

Synthesis of nanocrystals is one of the most rapidly advancing areas of nanoscience, and today nanocrystals can be produced with impressive control over their composition, size, shape, polydispersity, and surface chemistry. As such, they are ideal building blocks for fabricating hierarchical architectures with tailorable functionality on every level of the hierarchy. Here an evaporation-driven, template-assisted nanocrystal assembly (ETNA) technique is developed, providing a novel and general approach to fabricating freestanding, 3D, functional architectures using diverse combinations of colloidal nanocrystal species and porous templates of arbitrary geometry. Colloidal PbS (photoluminescent) and CoFe2O4 (superparamagnetic) nanocrystals are template-assembled to fabricate freestanding nanorods and inverse opals, which retain the size-dependent properties of their constituent building blocks while replicating the geometry and preserving the functionality of the templates. Further multifunctionality is demonstrated through mixed-nanocrystal architectures which exhibit the aggregate functionality of their building blocks.

Synthesis of nanocrystals is one of the most rapidly advancing areas of nanoscience, and today nanocrystals can be produced with impressive control over their composition, size, shape, polydispersity, and surface chemistry. As such, they are ideal building blocks for fabricating hierarchical architectures with tailorable functionality on every level of the hierarchy. Here an evaporation-driven, template-assisted nanocrystal assembly (ETNA) technique is developed, providing a novel and general approach to fabricating freestanding, 3D, functional architectures using diverse combinations of colloidal nanocrystal species and porous templates of arbitrary geometry. Colloidal PbS (photoluminescent) and CoFe2O4 (superparamagnetic) nanocrystals are template-assembled to fabricate freestanding nanorods and inverse opals, which retain the size-dependent properties of their constituent building blocks while replicating the geometry and preserving the functionality of the templates. Further multifunctionality is demonstrated through mixed-nanocrystal architectures which exhibit the aggregate functionality of their building blocks.

A new class of polymer stabilized gadolinium trifluoride nanoparticles (NPs) have been developed as contrast agents for magnetic resonance imaging (MRI) and computed tomography (CT), with potential long term goals in targeted imaging and anti-cancer therapy. The NPs are comprised of a 90/10 mixture of GdF3/EuF3 and are coated with linear polyacrylic acid (PAA) chains consisting of 25 repeating units. The resulting aggregates are stable in serum and possess unprecedented mass relaxivities [i.e. ~100-200 s-1(mg/mL)-1]. Electron microscopy images reveal various NP morphologies which depend on the exact synthesis protocol. These include highly cross-linked oblong clusters with 30-70 nm cross sections, extensively cross-linked aggregates with 100-300 nm cross sections, and distinct polymer stabilized nanocrystals with 50 nm diameters. Their application as contrast agents in T1-weighted MRI studies, CT imaging at various X-ray energies, and preliminary rat brain perfusion studies was also tested. NP contrast enhancement was compared to Gd-DPTA (Magnevist®) and iopramide (Ultravist 300®) to demonstrate their high contrasting properties and potential as multimodal contrast agents.

Studies various nanostructured materials have gained considerable interest within the past several decades. This novel class of materials has opened up a new realm of possibilities, both for the fundamental comprehension of matter, but also for innovative applications. The size-dependent effect observed for these systems often lies in their interaction with the surrounding environment and understanding such interactions is the pivotal point for the investigations undertaken in this thesis. Three families of nanoparticles are analyzed: semiconductor quantum dots, metallic silver nanoparticles and rare-earth oxide nanomaterials. The radical scavenging ability of cerium oxide nanoparticles (CeO2) is quite controversial since they have been labeled as both oxidizing and antioxidant species for biological systems. Here, both aqueous and organic stabilized nanoparticles are examined in straightforward systems containing only one reactive oxygen species to ensure a controlled release. The apparent absence of their direct radical scavenging ability is demonstrated despite the ease at which CeO2 nanoparticles generate stable surface Ce3+ clusters, which is used to explain the redox activity of these nanomaterials. On the contrary, CeO2 nanoparticles are shown to have an indirect scavenging effect in Fenton reactions by annihilating the reactivity of Fe2+ salts. Cadmium selenide quantum dots (CdSe QD) constitute another highly appealing family of nanocolloids in part due to their tunable, size-dependent luminescence across the visible spectrum. The effect of elemental sulfur treatment is investigated to overcome one of the main drawbacks of CdSe QD: low fluorescence quantum yield. Herein, we report a constant and reproducible quantum yield of 15%. The effect of sulfur surface treatment is also assessed following the growth of a silica shell, as well as the response towards a solution quencher (4-amino-TEMPO). The sulfur treated QD is also tested for interaction with pyronin Y, a xanthene dye that offers potential energy and electron transfer applications with the QD. Interaction with the dye molecule is compared to results obtained with untreated quantum dots, as well as CdSe/ZnS core shell examples. In another chapter of this thesis, the catalytic potential of silver nanoparticles is addressed for the grafting of polyhydrosiloxane polymer chains with various alkoxy groups. A simple one-pot synthesis is presented with silver salts and the polymer. the latter serves as a mild reducing agent and a stabilizing ligand, once silver nanoparticles are formed in-situ. We evaluate the conversion of silane into silyl ethers groups with the addition of several alcohols, whether primary, secondary or tertiary, and report the yields of grafting under the mildest conditions: room temperature, under air and atmospheric pressure.

This thesis examines the effects of nanoparticle, metal-oxide additives on the burning rate of composite solid propellants. Recent advancements in chemical synthesis techniques have allowed for the production of improved solid rocket propellant nano-scale additives. These additives show larger burning rate increases in composite propellants compared to previous additive generations. In addition to improving additive effectiveness, novel synthesis methods can improve manufacturability, reduce safety risks, and maximize energy efficiency of nano-scale burning rate enhancers. Several different nano-sized additives, each titania-based, were tested and compared for the same baseline AP/HTPB formulas and AP size distributions. The various methods demonstrate the evolution in our methods from spray-dried powders to pre-mixing the additive in the HTPB binder, and finally to a method of producing the additive directly in the binder as a nano-assembly. Burning rate increases as high as 80% at additive mass loadings of less than 0.5% were seen in non-aluminized, ammonium perchlorate-based propellants over the pressure spectrum of 500 psi (3.5 MPa) to 2250 psi (15.5 MPa). Increases in burning rate up to 73% were seen in similarly formulated aluminized propellants. During the past several years, the research team has refined laboratory-scale techniques for quickly and reliably assessing the mixing and performance of composite propellants with catalytic nanoparticle additives. This thesis also documents some of the details related to repeatability, accuracy, and realism of the methods used in the team’s recent nano-additive research; it also introduces the latest techniques for producing propellants with nano-sized additives and provides new burning rate results for the entire scope of additives and mixing methods. Details on the propellant characterization methods with regard to physical and combustion properties are provided. Snapshots from atmospheric propellant combustion videos taken with a Photron FASTCAM SA3 high-speed camera are included along with existing pressure and light-emission responses.