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Study of Thin Liquid Film Drainage and Interaction Forces in Organic Solvent for Liquid/Solid and Liquid/Liquid Interactions Using Dynamic Force Apparatus (DFA)

  • Author / Creator
    Ivanova, Nina Olegovna
  • Properties of thin liquid films between two approaching droplets or between a droplet and a solid surface are critical for emulsion stability and for mineral flotation. If the thin liquid film is stable, no coalescence occurs, while an unstable film will lead to rupture and coalescence or the formation of a three-phase contact line. While many studies have been conducted on the drainage of thin liquid films in aqueous media using techniques such as the Surface Force Apparatus (SFA) or Atomic Force Microscopy (AFM), fewer have been undertaken in organic media. Hydrodynamic effects, while important in many practical applications, are neglected in most studies by limiting approach speeds to low Reynolds numbers. This thesis focuses on understanding thin film behaviour and surface forces involved in the interaction of water/water and water/solid in “clean” and “contaminated” organic systems.

    A Dynamic Force Apparatus (DFA), which allows for simultaneous measurement of interfacial film thickness, drainage time and interaction forces at precisely controlled approach velocities, was used to study the interactions of a water drop with solid surfaces or between two water drops in organic liquids. For the “clean” system, two types of organic solvents were used: toluene and n-heptane (with and without water saturation). In the case of n-heptane, a very fast film rupture occurred for fully water-wettable hydrophilic silica and mica, with a very long-range attractive force observed (in the mm range), capable of deforming the interacting water droplet(s) prior to contact. It was shown that increasing substrate n-heptane immersion time, droplet salt concentration, approach velocity and pH decreased the observed long-range force and droplet elongation, with the opposite effect (increased attractive force, drop elongation) observed for water-saturated n heptane; high pH was found to increase drop elongation for drop/drop interactions. In the case of toluene, sapphire or all hydrophobized substrates, no elongation of droplet(s) or long-range force was observed.

    For the “contaminated system”, the fundamental behaviour of thin organic liquid films (containing the asphaltene model compound C5PeC11) between a droplet and solid surface was elucidated using a temperature-controlled DFA cell. A water droplet in 0.1 g/L C5PeC11-in-toluene solution was driven towards a silica surface of varying wettability (contact angles of 0° and 107°) at two different droplet approach velocities (0.1, 1 mm/s) and temperatures (22°C, 40°C). The observed spatiotemporal thin film drainage dynamics and interaction force agreed well with the prediction of the Stokes-Reynolds-Young-Laplace (SRYL) theoretical model. Rupture of thin liquid films between a water droplet and silica surfaces was observed, with moving three phase contact line and strong attachment for hydrophilic silica and minor, local attachment and an easily detachable water drop for hydrophobic silica. Increasing the approach velocity of water droplets towards solid surfaces resulted in a larger dimple and longer film lifetime. Interestingly, higher temperature led to a faster film rupture for hydrophilic silica, in line with industrially observed improvements in bitumen production for the removal of water-in-oil emulsions at higher temperatures during froth treatment.

    The major contributions to science of this thesis are the detection of a novel, extra long-range attractive force in a “clean” n-heptane system observed between water/(silica or mica) and water/water that cannot be described by current DLVO theory. The DFA was used to quantify the effect of salt concentration, pH, approach velocity, solvent immersion time and solvent water saturation on the extra long-range attractive force in the “clean” n-heptane system. The interaction forces and thin film drainage were also explored for other “clean” systems where no such long-range force was observed, namely hydrophobized surfaces and sapphire. Finally, in the “contaminated” system, the effect of velocity, wettability and temperature were elucidated for a water droplet driven toward a silica surface in a dilute C5PeC11/toluene solution, with the results in good agreement with the SRYL theoretical model.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
    Thesis
  • Degree
    Doctor of Philosophy
  • DOI
    https://doi.org/10.7939/r3-wara-3b23
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.