Dynamic behaviour during liquid-liquid phase separation within 2D confinement

  • Author / Creator
    Arends, Gilmar Friedrich
  • Fluid transport within confinement is important for many lab-scale and industrial-scale technological processes ranging from membrane separation, enhanced oil recovery, CO2 sequestration to drug delivery systems. At the industrial scale, confined liquids are often quite complex as they consist of several chemical components and phases. The physicochemical properties of the confined fluid and displacing fluid can impact fluid transport in many ways. More specifically, differences in the solubility of species can drive liquid-liquid phase separation, which often results in chemical composition gradients influencing the displacement rate. One of the major challenges is to improve fluid transport in confinement which is primarily driven through diffusion.

    The work in this thesis explores the effects of liquid-liquid phase separation on the displacement process of confined ternary liquid mixtures in a quasi-2D microchannel. The ternary mixtures consisted of a model oil component, a good solvent (ethanol) and a poor solvent (water). The mixtures were displaced and diluted by a penetrating liquid consisting of water or ethanol aqueous solution. The first part of the work reveals that the initial ternary solution composition affects the spatial distribution of subphases formed by phase separation and the displacement rates of the solutions producing distinct phase separation behaviours. The boundary between the confined ternary liquid and the penetrating liquid changes from a defined interface to a diffusive interface by reducing the initial 1-octanol composition. The boundary displacement rate was found to vary non-linearly as a function of the initial 1-octanol solution composition. The slowest boundary displacement rates were found at an intermediate 1-octanol composition. However, the rate was still 2 times faster than expected for a purely diffusive process. At low 1-octanol compositions (2-20 wt-%), fast displacement rates were associated with droplet formation and movement driven by local composition gradients formed during phase separation.

    The second part of the work investigates the direction and speed of propelling microdroplets driven by local chemical composition gradients from liquid-liquid phase separation within confinement. The microdroplets, ~1/4-1/3 the height of a narrow channel, form and move spontaneously as the ternary solution mixes with water diffusing from a deep side channel. The local composition gradients were estimated from fluorescence intensity measurements, and microdroplet movement was followed in situ using high-speed bright field imaging. From the phase separation of a ternary solution with high oil composition, propelling oil-rich microdroplets formed within a water-rich phase zone, along with water-rich microdroplets in an oil-rich phase zone. The oil-rich propelling microdroplets induce a directional flow transport that mobilizes water-rich microdroplets close to water-rich zones. Microdroplet displacement scaled linearly with time regardless of the solution compositions, while average droplet speed increased with initial oil composition displaying speeds up to 150 µm/s along the surface of the hydrophobic wall. The presence of a sharp ethanol concentration gradient is believed to be the primary driving force for the fast movement of oil-rich microdroplets. Overall, the knowledge gained from this thesis improves the understanding of fluid transport within confinement, particularly for systems undergoing liquid-liquid phase separation. The work highlights the potential of using phase separation as a functional strategy to improve multicomponent liquid flow within confinement applicable for a wide range of separation processes.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • 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.