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Removal of emulsified water is a challenge in oil sands and heavy oil processing. The flocculation and coagulation of emulsified water droplets depend on the interactions between the water droplets covered mainly by asphaltenes and oil-contaminated fine solids. To quantitatively evaluate the stability of water-in-diluted bitumen emulsions, this research determined the interactions between asphaltene surfaces in model oils, heptane, toluene or a mixture of the two known as heptol, by colloidal force measurements using atomic force microscopy (AFM) in combination with the Langmuir-Blodgett technique. The effect of aromaticity of the solvents, temperature and water content of the solvents on asphaltenes-asphaltenes interactions was systematically investigated. The results showed that the interaction forces between asphaltenes are highly sensitive to the aromaticity of the organic solvents. In solvents of higher aromaticity, a repulsive force existed between asphaltene surfaces; whereas in solvents of lower aromaticity, a weak attraction was detected. The transition from repulsion to attraction indicates that it is possible to control asphaltenes-asphaltenes interactions, and ultimately to control the stability of asphaltene-stabilized water droplets in oil, through tuning the aromaticity of the organic solvents. By fitting the measured force profiles with theoretical models, the nature of the forces was determined, which provides insights into the mechanisms of asphaltene-stabilized water-in-oil emulsions. The concomitant benefit of the results from the direct force measurement is to predict asphaltene precipitation with change of solvent composition. Oil-contaminated fine solids not only help stabilize water-in-diluted bitumen emulsions but are detrimental to bitumen upgrading. To control the wettability of these fine solids, a preliminary study was carried out in this work to explore the potential of ethyl cellulose (EC), an effective demulsifier for water-in-diluted bitumen emulsion, as a surface wettability modifier of the oil-contaminated solids. It was found that EC is able to reduce the surface hydrophobicity of the asphaltene- and bitumen-contaminated solids and thus enhances their removal from bitumen froth. The mechanism of increased wettability by EC addition was determined by quartz crystal microbalance with dissipation (QCM-D) and AFM topographical imaging. The results from this study can help establish the criteria for selecting and developing chemical modifiers for applications in wettability control of oil-contaminated solids. / Chemical Engineering

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I have studied the effects of polydispersity on the phase behaviour of suspensions of PMMA colloidal spheres on their own and in the presence of non-adsorbed polymer. I systematically explored the volume fraction-polydispersity phase behaviour of hard spheres (with radii R =167, 244, 300 and 303nm) through direct observations and crystallography measurements. I observed normal crystallisation for sigma < 7:5%, and no crystals at sigma > 18%. Samples at sigma ~~ 9.5% showed crystal-fluid coexistence between 0:52 < phi < 0:56 but no fully crystalline be- haviour above this region. This may be explained by slow particle diffusion in the dense metastable fluid and a glass transition, possibly involving only the larger particles. The addition of random coil polymer (radius of gyration rg) to a suspension of single-sized spherical colloidal particles induces an attractive depletion potential which, for size ratios Xi = rg=R < 0:2, has the effect of expanding the crystal-fluid coexistence region. Surprisingly, when such a polymer solution (with Xi = 0:1), with a range of concentrations cp, is added to a polydisperse colloidal suspension (sigma ~~ 10%), crystal formation is actually suppressed. This can be explained by the fact that the polymer compresses the nascent crystal phase to volume fractions greater than the maximum phi permitted for polydisperse spheres. By modifying existing free energy equations to include the effects of colloidal polydispersity we also succeed in reproducing the observed phase diagram. Larger added polymer (Xi > 0:3) introduces a region of stable gas-liquid coexistence. In systems where crystallisation is suppressed due to polydispersity, this will theoretically be the only transition. By preparing many samples over a range of phi and cp this prediction was observed experimentally for Xi = 0:5. Fractionation studies on coexisting phases enabled verification of a recent universal law of fractionation in slightly polydisperse systems.

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This dissertation describes the use of spherical micro- and nanoparticles as building blocks for the fabrication of colloidal crystals. The polymer component used in all of the projects that are described herein is poly-N-isopropylacrylamide (pNIPAm). The polymeric identity of particles composed of this soft, hydrogel material, which is also thermoresponsive, contributes to particle self-assembly to form ordered structures. Specifically, particles that possess a core/shell topology were investigated to allow for the localization of distinct polymeric properties. Chapter 2 examines a characterization technique using fluorescence resonance energy transfer (FRET) that was explored to investigate the structure of pNIPAm particles that possess this core/shell topology. Chapters 4-6 investigate strategies to impart both stability and flexibility to the particles so that these properties could assist in particle self-assembly as well as provide a stable construct for the production of robust crystalline materials. Styrene was used as the main monomer component in a copolymer synthesis with NIPAm to achieve poly(styrene-co-N-isopropylacrylamide particles (pS-co-NIPAm) that exhibited both hard and soft properties. Simple drying procedures were used to form crystal assemblies with these particles and the application of these pS-co-NIPAm particle suspensions as processable, photonic inks is also investigated. Chapter 7 examines the ability to physically cross-link colloidal crystals composed of pS-co-NIPAm particles by simple heating methods to produce robust films. The optical properties of these crystal films could be tuned by simple rehydration of the film due to the hydrogel character of the crystal building blocks. Chapters 3 and 5 examine the synthesis and self-assembly strategies of core/shell particles using the properties of pNIPAm shell layers that have been added to different types of core particles (silver or pS-co-NIPAm) for the purposes of fabricating colloidal crystals with enhanced properties using thermal annealing procedures. Chapter 8 explores the use of silver particles as tracers for the characterization of colloidal crystals composed of thermally annealed colloidal crystals composed of pNIPAm hydrogel particles.