A systematic research study was carried out in order to characterize the rheology of concentrated slurries prepared from eight nickel laterites. The experiments were carried out using a rotational viscometer, and the behavior of the laterites was evaluated in terms of the apparent viscosity and yield stress obtained through flow curve modeling. An attempt was made to correlate the results obtained for the laterite samples with data obtained for model single mineral systems as well as for model mixed mineral systems. In combination with detailed mineralogical characterization of the laterite samples, all the rheological results allowed a rheology-based laterite classification system to be proposed. Accordingly, the laterite samples gave the following responses: the SAPSIL samples (high-quartz) generally producedl ow yield stress values, the SAPFE samples (high-iron) were characterized by intermediate to high yield stress values, while the SAP samples (saprolite) gave the highest yield stress values. Interestingly, these dominant rheological responses of laterites could actually be predicted based on rheological tests carried out on model mineral suspensions (particularly goethite and quartz). Since the rheology of fine mineral suspensions is largely determined by the surface properties (surface charge) of the particles, a series of electro-acoustic measurements were also performed on model minerals and laterite samples to analyze the surface charge characteristics of the tested samples. It was demonstrated that the current electro-acoustic theory developed for single mineral systems can readily be used for modeling the behavior of mixed mineral systems. The modeling and experimental data agreed exceptionally well when constituent minerals were of the same surface charge under given pH. Clear but rather small deviations between experiment and theory were observed under conditions when the minerals were oppositely charged. This observation strongly suggested that inter-particle aggregation was most likely responsible for the observed discrepancies. Overall, the results of this thesis show that laterite slurries exhibit a wide range of rheological responses due to highly variable mineralogy, differences in particle size distributions, and difference in the surface properties of the many constituent minerals. It also shows that the surface properties of the minerals relates to rheology.

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The overall objective of this PhD thesis research is to characterize, understand and ultimately control phase-separated structures in mixed films consisting of a perfluorinated fatty acid and a photopolymerizable surfactant. In these systems, film morphology, mechanical properties and spectroscopic properties are inter-related and this thesis explores these relationships. In this context the interaction between perfluorotetradecanoic acid (C13F27COOH, referred to as PF in this dissertation), and 10,12-pentacosadynoic acid (CH3(CH2)11−C≡C−C≡C−(CH2)8COOH, referred to as PCDA in this dissertation) has been studied in monolayers using a combination of surface and spectroscopic characterization techniques. To investigate the inter-relationship of the properties described above, film behavior under a variety of conditions, including behavior at different interfaces (solid-liquid, air-liquid), different film compositions and under different conditions of photoillumination and mechanical stress were explored. Thermodynamic and morphological studies of mixed monolayer surfactant films of PF and the photo-polymerizable diacetylene molecule, PCDA, were carried out. The films were prepared at the air-water interface and transferred onto solid supports such as a glass slides via Langmuir-Blodgett (LB) deposition technique. The presence of the perfluoroacid helped to stabilize the diacetylene surfactant monolayer in comparison with the diacetylene alone, allowing film transfer onto solid substrates without needing to add cations to the sub-phase or photo-polymerize the components prior to deposition. Addition of the perfluorocarbon to PCDA resulted in films with the photopolymer strands oriented perpendicular to the direction of the film compression in a Langmuir trough. This is in contrast with film structures formed from pure PCDA. Formation of these features could be explained by a two-step process that happened sequentially: first, the compression of monolayer with trough barriers while trying to maintain the surface pressure constant induces stress on the film surface; second, additional film buckling which was enhanced by the strong cohesion between PF and PCDA. Film compression data, supported by in situ fluorescence spectrophotometry, Brewster angle microscope imaging and atomic force microscope images of deposited films, supported this mechanism. Factors that controlled the orientation of the photopolymer fibers were also investigated. Fibers were found to consist of multiple strands, with each strand having a different orientation. Our investigation also revealed there was a preferred orientation for fibers in the film as a whole. The angle of approximately 60o to the direction of film compression during deposition from a Langmuir trough has been calculated with the help of dual-view, polarized fluorescence microscopy. This orientation was attributed to the mechanical stress exerted by the trough compression barriers coupled with rotation of the polymer fibers during film draining. The combination of Atomic Force Microscope (AFM) and fluorescence microscopy (FM) provided a thorough and comprehensive mapping of fundamental properties of mixed monolayer system, and enabled a quantitative determination of the degree of selectivity of the polymerization process.

Diamond is of interest as an advanced functional material, since the extreme physical properties of diamond, suggests it is ideally suited to a range of new demanding applications. In this context, the thesis explores basic surface chemical properties of diamond thin films, along with electrochemical, electronic and electron emission processes involving this material. New experiments are reported concerning the nature of surface conductivity on diamond. Measurements clearly show that the conductivity only arises if a hydrogenated diamond surface is exposed to water vapour, in the presence of chemical species capable of acting as electron acceptors. The conduction properties of surface conductive diamond in aqueous solution are also studied, and the first detailed electrochemical investigations of this material are described. Comparative electrochemical studies of nanocrystalline and boron-doped diamond have been performed. Investigations of electrode stability, and the accessible "potential window" are described, as well as the behaviour of a range of 'redox' systems, including transition metal complexes, metal deposition/stripping, and bio-related organic species. Significant differences between the behaviour of nanodiamond and microcrystalline boron-doped material are observed. A range of surface chemical and threshold photoemission studies of diamond thin films are reported. The results indicate that quantum photoyields (QPYs) are insensitive to the diamond "quality", although the wavelength selectivity is dependent on it. The adsorption of oxygen strongly reduces the QPY, although this only occurs slowly in the presence of O₂ because of a low reactive sticking probability. Much more rapid uptake of oxygen and consequent reduction of photoyield is observed in the presence of atomic O or electronically excited dioxygen O₂*. The presence of alkali metals on the diamond surface increases the QPY, and reduces the sensitivity of the QPY to surface oxygen. Significant differences between the surface chemical properties of Li, and other adsorbed akali metals (K and Cs) are observed.

The effect of orientation and crystallinity of certain polymers, polyethylene, polypropylene, polyethylene terephthalate (PET) and poly (ether ether ketone) (PEEK) , upon the extent and nature of plasma oxidation was studied. It was found that increasing the extent of surface ordering lessened susceptibility to plasma oxidation and reduced the subsequent decay of surface treatment. The surface ageing of plasma oxidised PEEK was extensively studied with regards to the transient increase in hydrophilicity that has been observed after plasma modification. The decay and transient increase in hydrophilicity were found to be dependent upon crystallinity and storage temperature. An estimate of the activation energies for processes leading to the increase in contact angle after plasma modification were calculated and found to suggest that these processes were rotational reorganisations at the surface as opposed to migrational reorganisations. The decay of other plasma modified surfaces revealed that plasma oxidised PET and plasma fluorinated PEEK both underwent transitional reorganisations at the surface, however no such change was observed for ammonia plasma treated PEEK. Plasma modification of carbon fibres was investigated with regards to improving composite performance. Microwave plasma treatments were found to be as good as standard commercial treatments. Graphitic carbon was investigated as a model for carbon fibre surfaces, however, the plasma modified surface was found to age more readily and to be too labile for useful comparison.

Theoretical studies on the wetting of cylindrical solid surfaces with axisymmetric rugosities explicitly showed the presence of contact angle hysteresis, non-equilibrium jumps during contact line motion and the formation of composite surfaces. For physically rough surfaces with unidirectional randomness it was shown that hysteresis increases with decreasing roughness dimensions and with increasing standard deviation in the solid surface slope distribution. / The wetting of solid surfaces by liquids was investigated by a new tensiometric technique called capillarography. At large roughness wavelengths ((TURN)100 (mu)m) the contribution of concentric sawtooth-shaped regular roughness was found to be close to the values calculated theoretically. At smaller roughness wavelengths ((TURN)1 (mu)m) the wetting is complicated by intrinsic roughness and chemical heterogeneity. / High energy surfaces such as platinum and quartz exhibit a regular stick-jump behavior when wetted with water above a very low critical contact line velocity. This is caused by minute amounts of surface active impurities in the system. From the experimental data it can be deduced that surface active molecules diffuse onto and over the solid surface. / A relaxation of the contact angle was observed when an initially slow moving contact line was brought to a full stop. This is attributed to the slow establishment of a new equilibrium, possibly by surface capillary waves, involving metastable contact line positions separated by energy barriers. For receding contact angles, the main cause of the relaxation seems to be a stabilization of a liquid film left behind a receding contact line. / The observations made in this study contribute to a better understanding of the complicated nature of the wetting of solids.

A systematic research study was carried out in order to characterize the rheology of concentrated slurries prepared from eight nickel laterites. The experiments were carried out using a rotational viscometer, and the behavior of the laterites was evaluated in terms of the apparent viscosity and yield stress obtained through flow curve modeling. An attempt was made to correlate the results obtained for the laterite samples with data obtained for model single mineral systems as well as for model mixed mineral systems. In combination with detailed mineralogical characterization of the laterite samples, all the rheological results allowed a rheology-based laterite classification system to be proposed. Accordingly, the laterite samples gave the following responses: the SAPSIL samples (high-quartz) generally producedl ow yield stress values, the SAPFE samples (high-iron) were characterized by intermediate to high yield stress values, while the SAP samples (saprolite) gave the highest yield stress values. Interestingly, these dominant rheological responses of laterites could actually be predicted based on rheological tests carried out on model mineral suspensions (particularly goethite and quartz). Since the rheology of fine mineral suspensions is largely determined by the surface properties (surface charge) of the particles, a series of electro-acoustic measurements were also performed on model minerals and laterite samples to analyze the surface charge characteristics of the tested samples. It was demonstrated that the current electro-acoustic theory developed for single mineral systems can readily be used for modeling the behavior of mixed mineral systems. The modeling and experimental data agreed exceptionally well when constituent minerals were of the same surface charge under given pH. Clear but rather small deviations between experiment and theory were observed under conditions when the minerals were oppositely charged. This observation strongly suggested that inter-particle aggregation was most likely responsible for the observed discrepancies. Overall, the results of this thesis show that laterite slurries exhibit a wide range of rheological responses due to highly variable mineralogy, differences in particle size distributions, and difference in the surface properties of the many constituent minerals. It also shows that the surface properties of the minerals relates to rheology.