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The effect of impurities on crystal morphology is a challenging problem, since even at low concentrations they can have drastic effects on the final habit. Industrially this causes problems with downstream processes such as filtration, processability and even storage. Conversely, structurally related additive molecules may be introduced to a system in order to mimic the effect of an impurity resulting in a beneficial effect on problematic crystal morphologies. The work presented here considers the design and use of tailor made additives on a nonhydrogen bonded crystal, benzophenone. This compound is typical of many agrochemical materials in that the major intermolecular interactions are of the nondirectional van der Waals type. Using crystal packing analysis a selection of additives has been chosen with the intent of specifically hindering certain directions of crystal growth. From an initial group of nine molecules two additives, 4ABP and 4MBP were found tobe particularly effective, both strongly hindering growth. Measured kinetic data suggests that these additives bind to steps in the growth spirals, drastically slowing growth of specific crystal faces altering the crystal morphology to a needle shape. Through nucleation experiments and product analysis the additives were shown to effect only crystal growth becoming incorporated into the crystal structure. Computational modelling of the binding of additives to the crystal surfaces of benzophenone has been used in an attempt to rationalise the experimental effects. In many cases calculated binding energies were in agreement with experimental observation. However, modified attachment energies did not match well with experimental observations.

Abstract: The interaction between bubbles and solid surfaces is important to a broad range of industrial and biological processes. Various experimental techniques have been developed to measure the interactions of bubbles approaching solids in a liquid. In this thesis the consistency and accuracy of such measurement are tested against Stokes-Reynolds-Young-Laplace model in which the augmented Young Laplace equation is linearized within the interaction zone. The main focus of this thesis is to model thin liquid film drainage using the non-linearized Young Laplace equation in combination with the Stokes Reynolds equation. The scaled equations of the non-linearized SRYL model do not have a universal nature and depend on the physical parameters of system via capillary number. The numerical results show that in contrast to the linearized SRYL model, the hydrodynamic resistance force predicted from the non-linearized SRYL model strongly depends on the capillary number, Ca. The non-linearized SRYL model is compared with the linearized SRYL model at a broad range of capillary number from 10-8 to 10-3. The numerical results show that at low Ca number of 10-8 and smaller, both the non-linearized and linearized SRYL models lead to the same prediction for bubble deformation, time dependent force and hydrodynamic force. Therefore, over this range of Ca number both the non-linearized and linearized SRYL models can be confidently used to obtain the spatial and temporal evolutions of the film profile, once these models are shown to be able to give an accurate prediction of time dependent force profiles. For systems of Ca number larger than 10-8, the linearized SRYL model predicts a stronger hydrodynamic repulsive force, and the maximum difference in prediction between the two models occurs at the Ca number around ~ 3.4×10-5. The numerical results show that in comparison with the non-linearized SRYL model at the same rmax (the boundary of the solution domain), the linearized SRYL model overestimates the hydrodynamic resistance force for the Ca numbers tested which in turn influences the prediction of bubble deformation and time dependent force profiles. However over this high Ca number range, both the non-linearized and linearized SRYL models can predict the same time dependent force profiles with different overlaps (different adjustable parameters), while there are differences in the prediction of bubble shape and hydrodynamic repulsive force. Therefore, even if the linearized SRYL model is shown to be able to give an accurate prediction for time variations of the interaction forces over this range of Ca numbers, we cannot confidently use the linearized SRYL model to predict the spatial and temporal evolutions of the shape of the film trapped between interacting interfaces. Validation of simulation results by thin film profile measurement using thin film force apparatus (TFFA), conclude that the non-linearized SRYL model is more accurate for high Ca number systems. For a system of very high capillary numbers the non-linearized SRYL model predicts a solid-like bubble that does not deform in the approach phase. In contrast, the linearized SRYL model is unable to show the bubble rigidity at high capillary numbers. Furthermore the non-linearized SRYL model is able to predict the critical bubble approach velocity above which the bubble behaves like a solid sphere. This study shows that the non-linearized SRYL model is needed to study the effect of individual parameters of system such as bubble size, interfacial tension and liquid viscosity on the critical bubble approach velocity at which bubble behaves like a solid sphere. The non-linearized SRYL model is used to model the measurements of the recently developed integrated thin film drainage apparatus (ITFDA) which has been used to measure the bubble-particle interactions over a wide range of hydrodynamic conditions. The excellent agreement between the predicted and measured interaction forces between an air bubble and solid surface in three liquids of very distinct physicochemical properties demonstrates that the non-linearized SRYL model can be applied to the systems of a wider range of bubble approach velocity, liquid interfacial tension and viscosity. The excellent agreement suggests that the non-linearized SRYL model can be used to obtain quantitative information on film profiles during the bubble approach-retract cycle. The simulation results indicate that the minimum film thickness between an air bubble and hydrophilic solid surface in a liquid over a given approach period is thinner for the system of low bubble approach velocity, and/or low viscosity and high surface tension of the liquids. In this thesis the non-linearized SRYL is further developed to account for the effect of solid surface hydrophobicity. The experimental data quantified with the integrated thin film drainage apparatus (ITFDA) and the thin film force apparatus (TFFA) was used to validate the extended non-linearized SRYL model. The hydrophobic force which was considered as the driving force for destabilizing water films on hydrophobic surface was evaluated with the best fit between the measured and predicted time evolution forces. The numerical results showed that the longer-range hydrophobic force with increasing the surface hydrophobicity was responsible for film rupture. The effect of surface hydrophobicity and bubble approach velocity on the drainage rate of intervening liquid film was studied. The results showed that the wetting films formed on hydrophobic glass sphere of increasing surface hydrophobicity, thin much faster. Film drainage resistance or force barrier are determined to reduce greatly with increasing the solid surface hydrophobicity. Moreover the film drainage resistance or force barrier is found to increase with increasing bubble approach velocity. Decreasing bubble approach velocity or/and increasing surface hydrophobicity are found to decrease the film radius. As a result the film ruptures at locations closer to the center of the film. The extended non-linearized SRYL model incorporating proper form of hydrophobic force is able to predict the critical film thickness where the film ruptures. The prediction of the critical film thickness is achieved by solving non-linear SRYL equations without simplifications. The simulation results indicate that the critical film thickness increases with increasing surface hydrophobicity and bubble approach velocity.

Abstract: As one of the most critical steps to recover valuable particles from a slurry using flotation, knowledge of the drainage of the thin liquid film between an air bubble and a solid surface is required. The main focus of this thesis is to develop and use an integrated thin film drainage appratus (ITFDA) to investigate the physicochemical properties of the aqueous liquid film between an air bubble and a solid surface under dynamic conditions. The ITFDA was designed to measure drainage dynamics of thin liquid films confined between a solid particle, a gas bubble or/and an immiscible liquid droplet. Equipped with a bimorph force sensor, a computer-interfaced video capture device and a data acquisition system, this custom-made ITFDA allowed us to measure directly and simultaneously hydrodynamic forces, true liquid film drainage time under a well controlled external force, receding and advancing contact angles, capillary force, and detachment force between an air bubble or oil droplet and a solid, a liquid or an air bubble in an immiscible liquid. Using a diaphragm of a high frequency speaker as the drive mechanism for the air bubble or oil droplet attached to a capillary tube, this new device is capable of accurately and independently measuring forces over a wide range of hydrodynamic conditions, including bubble approach and retract velocity up to 50 mm/s and displacement range up to 1 mm. Using this device, interactions between an air bubble and a hydrophilic or hydrophobized glass sphere were measured. The results showed that the ITFDA was capable to accurately measure hydrodynamic resistance between air bubbles and solid particles in aqueous solutions, providing direct evidence of the critical roles of hydrodynamic forces and particle hydrophobicity in air bubble and particle interactions. The results from this study also showed a close relationship between bubble drive velocity, solid hydrophobicity and force barrier before three phase contact of air bubbles on hydrophobized solids in aqueous solutions. Solution pH, salt concentration and surfactant all have effects on the solid hydrophobicity, and hence change the bubble-hydrophobic solid interactions.

The lithographic development of a silver iodobromide emulsion with thiocyanate substituted for bromide in a lith developer formulation showed differences in behavior with regard to induction time and maximum rate of development at equal levels of normality. An experiment was designed with development time, halide concentration, and exposure level as the variables with maximum rate of development, time to reach 0.20 optical density (induction time), and slope at 0.40 optical density as the response parameters. The maximum rate of development with the developer containing bromide was found to be significantly dependent upon exposure level and not significantly dependent upon bromide concentration in the range of 0.020 N to 0.058 N. Significant different exists between 0.000 N and all other levels of bromide. The maximum rate of development with developer containing thiocyanate was found not to be significantly dependent upon thiocyanate concentration nor exposure level. Induction time with the developer containing bromide is significantly dependent upon exposure level and not statistically dependent upon bromide concentration. Induction time with the developer containing thiocyanate is very significantly dependent upon thiocyanate concentration and exposure level. Slope at 0.40 optical density with the developer containing bromide is independent of bromide concentration from 0.020 N to 0.058 N and development time from 1.0 to 2.5 minutes. Slope at 0.40 density with the developer containing thiocyanate is independent of development time. Thiocyanate concentration is highly significant with the 0.000 N and 0.063 N levels as one population and the 0.021 N and 0.042 N levels as another population.