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Current problems on the interaction of complex liquids (i.e. droplets or foams) with complex surfaces (i.e. soft deformable or porous surfaces) are addressed in the following areas: (1) wetting of deformable substrates and surface forces, (2) kinetics of wetting and spreading of non-Newtonian liquids over porous substrates, (3) kinetics of spreading of non-Newtonian solutions over hair, (4) free drainage of foams produced from non-Newtonian solutions, and (5) foam drainage placed on porous substrates. Equilibrium of liquid droplets on deformable substrates was investigated and the effect of disjoining pressure action in the vicinity of the apparent three phase contact line was taken into account. It was proven that the deformation of soft solids is determined by the action of surface forces inside the transition zone. Spreading/imbibition of blood, which is a power law shear thinning non-Newtonian liquid, over a dry porous layer was investigated from both theoretical and experimental points of view. It was found that blood droplet spreading/imbibition over porous substrates shows two different behaviours: (i) partial wetting case with three subsequent stages: initial fast spreading, constant maximum droplet base and the shrinkage of the droplet base; (ii) complete wetting case with only two stages: initial fast spreading and the shrinkage of the droplet base. The wetting of hair tresses by aqueous solutions of two commercially available polymers, AculynTM 22 (A22) and AculynTM 33 (A33) was investigated experimentally. Both A22 and A33 solutions demonstrate well pronounced shear thinning behaviour. Initial contact angle of the A22 and A33 solutions on hair tresses was about 100o. The A22 droplets remained on the hair tress after spreading for at least half an hour. However, a fast penetration of the A33 droplets inside the hair tresses was observed when advancing contact angle in the course of spreading reached a critical value of about 60o. This could be explained by Cassie-Wenzel wetting transition which is caused by filling the pores inside the porous media by liquid. The influence of non-Newtonian rheology of A22 and A33 solutions on foam drainage was also investigated experimentally and a new theory of foam drainage was presented for the case of free drainage. For lowly viscous polymeric solutions and under the assumption of rigid surface of the Plateau border, the predicted values of the time evolution of the foam height and liquid content were in good agreement with the experimental data. However, in the case of highly viscous solutions an interfacial mobility at the surface of the Plateau border has to be taken into account. A completely new theory of foam drainage placed on porous substrate was developed. It was found that there are three different regimes of the process: (i) a rapid imbibition, the imbibition into the porous substrate dominates as compared with the foam drainage; (ii) an intermediate imbibition, that is, the imbibition into the porous substrate and the rate of drainage are comparable; (iii) a slow imbibition, the rate of drainage inside the foam is higher than the imbibition into the porous substrate for a period of time and a free liquid layer is formed over the porous substrate.

Foam fractionation is an adsorptive bubble separation technology that has shown potential as a replacement to the more costly and non-sustainable traditional downstream processing methods such as solvent extraction and chromatography for biological systems. However biological systems mostly tend to be a mixture of surface active species that complicates the foam fractionation separation. In this thesis a detailed experimental study on the application of foam fractionation to separate a well-defined surfactant-protein mixture was performed with emphasis on the competitive adsorption behaviour and transport processes of surfactant-protein mixtures in a foam fractionation process. Surface tension and nuclear magnetic resonance (NMR) measurements showed that nonionic surfactant Triton X−100 maximum surface pressure, surface affinity and diffusivity were a factor of 2.05, 67.0 and 19.6 respectively greater than that of BSA. Thus Triton X−100 dominated the surface adsorption at an air-water surface by diffusing to the surface and adsorbing at the surface faster than BSA. This competitive adsorption behaviour was observed in foam fractionation experiments performed for Triton X−100/BSA mixtures for different feed concentration ratios and air flow rates. The recovery and enrichment of Triton X−100 were found to increase and decrease respectively with increasing air flow rate for all foam fractionation experiments as expected for a single component system. However the recovery and enrichment of BSA were both found to increase with increasing air flow rate for high feed concentrations of Triton X−100.Bubble size measurements of the foamate produced from foam fractionation experiments showed that at steady state conditions the bubbles rising from the liquid pool were stabilised by BSA. However at the top of the column the recovery of Triton X−100 in the foamate (75% to 100%) was always greater than the recovery of BSA (13% to 76%) for all foam fractionation experiments. In addition, for high feed concentrations of both components and at low air flow rates, the enrichment of BSA remained at almost unity for most experiments and only increased when the recovery of Triton X−100 reached 100%. Thus it was concluded that Triton X-100 displaced the adsorbed BSA from the surface. The foam drainage properties of Triton X−100/BSA mixtures were characterised using two methods; forced foam drainage and from pressure profiles of steady state foam fractionation experiments (pressure method). The drainage data from the forced foam drainage was found not to be compatible with experimental foam fractionation results, by indicating that stable foam was not produced during the foam fractionation experiments. However stable foam was repeatedly produced during foam fractionation experiments. The drainage data from the pressure method was found to be in close agreement to experimental foam fractionation experiments. The work in this thesis takes a significant step beyond the literature experimental foam fractionation studies for multicomponent systems. In addition to investigating the effect of foam fractionation process parameters on the separation of mixed systems, the results from the characterisation studies of surface adsorption and foam properties provided insight and deeper understanding of the competitive adsorption behaviour of surfactants and proteins in a foam fractionation process.

Flotation is a complex, multiphase process used to separate minerals. Four problems central to the fundamentals of the flotation process were studied. A multiphase grid turbulence experiment was conducted to verify particle collision models. The slip velocities of solid particles and bubbles were measured using Digital Particle Image Velocimetry (DPIV). The experimental results were compared with the predictions from empirical and theoretical collision models. Time-resolved DPIV was used to measure the turbulent velocity field in a Rushton turbine around the impeller region. The turbulence quantities were found by removing the periodic component from the blade passing, which is a dominant part of the measured velocities near the impeller. We provide evidence that larger, biased dissipation and turbulent kinetic energy values are estimated in the vicinity of the impeller due to the periodic component of the blade passage. The flow was found to be anisotropic close to the impeller. Vortex detection revealed that the tip vortices travel in a nearly radial direction from the impeller for small Reynolds numbers and with a wider distribution for higher Reynolds numbers. The rise of a buoyant bubble and its interaction with a free liquid surface was experimentally investigated using Time-Resolved Digital Particle Image Velocimetry as a function of bubble size, and surfactant concentration of the fluid medium. It is shown that the presence of a surfactant significantly affected the characteristics of the velocity field during the rise and interaction with the free surface. This difference is attributed to the adsorption coverage of the surfactant at the bubble-fluid interface. Wake profiles were compared. The presence of large vortices were observed and found to play a significant role. Finally, Numerical and experimental results of stable and unstable foams are presented by comparing liquid fractions and bubble sizes. There was good agreement between the experiments and numerical modeling in free drainage and forced drainage experiments. In addition, foam coarsening was measured and characterized experimentally. Each of the problems investigated have added to the understanding in the underlying physics of the flotation process and can lead to more accurate modeling. The ultimate goal of this work is to contribute to the design of more effective and efficient flotation machines. / Ph. D.