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THE INTERACTION BETWEEN DEPLETION FLOCCULATION AND MOLECULAR LIQUID-LIQUID PHASE SEPARATION MECHANISMS

  • Author / Creator
    Kumar, Anupam
  • There is growing interest in the formulation and application of nano colloids + non-adsorbing polymer in fields of nanomedicine, hydrocarbon production, and environmental science. Successful applications rely on a detailed understanding of the related fluid thermophysical and thermochemical properties. Polymer + solvent binary mixtures exhibit liquid-liquid phase behavior at low temperature. This behavior, driven by repulsive interactions between the globular conformation of the polymer, possess an UCEP temperature because the polymer undergoes a conformational change. From a Gibbs free energy perspective, at temperatures slightly above the UCEP temperature, a single-phase liquid is marginally stable. This phase behavior is driven by entropically favourable molecular interactions between polymer in the coil conformation and solvent molecules. Phase diagrams for nanoparticle + non-adsorbing polymer + solvent ternary mixtures typically exhibit colloid gas, G (a liquid comprising largely polymer and solvent), a colloid liquid, L (a liquid comprising largely solvent and colloid) and a colloid phase, C (a largely nanoparticle rich phase) phases. The phase behaviors GC, GL, LC and GLC at equilibrium are driven by depletion flocculation (a surface phenomenon). This work focuses on the interaction between these two phenomena – depletion flocculation and molecular liquid-liquid phase behavior based on the behavior of polystyrene + cyclohexane + nano silica particles. For example, above the UCEP temperature, even a trace mass fraction of silica nanoparticle (<0.005) destabilizes the marginally stable polystyrene + cyclohexane mixture. The phase diagrams obtained in this work are discussed in relation to the UCEP temperature of the binary mixture polystyrene + cyclohexane (this work: 299 K). The interplay between molecular and colloidal effects leads to phase diagrams that were not previously anticipated. Some of these phase diagrams were observed directly. Other phase diagrams were inferred from phase diagram theory as transitional when colloid solid (C) and colloid gas (G) + liquid (L) phase behaviors overlap. Above the UCEP temperature, one new phase diagram including two colloid G=L critical points on a closed loop colloid G+L region was observed experimentally. A second new phase diagram with a L+G+C region and two colloid G=L critical points is inferred, but not observed experimentally, based on this work and prior work of others. Below the UCEP temperature, one new phase diagram was observed experimentally and a second new phase diagram was inferred based on measurements in this work and phase diagram theory. Implications of these findings and priorities for further study are introduced.

  • Subjects / Keywords
  • Graduation date
    Spring 2018
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/R3BZ61Q16
  • 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.