Influence of Switching Dynamics on the Solvent Extraction Process of Polymer Droplets

  • Author / Creator
    Billet, Romain
  • Switchable hydrophilicity solvents (SHSs) are solvents defined by their ability to switch from their hydrophobic form to a hydrophilic form when put in contact with an acidic trigger such as CO2. As a consequence, SHSs qualify as promising alternatives to volatile organic compounds during the industrial solvent extraction processes, as greener and inexpensive methods can be applied to separate and recover SHSs. Furthermore, because of their less volatile nature, SHSs are less flammable and so increase the safety of a larger-scale extraction process. However, the use of SHSs also comes with challenges related to the long switching times and high residual solvent left in extraction products.

    In the first part of this work, we study the dynamics and in-drop phase separation during the dissolution process of a sessile binary drop composed of the SHS N,N-Dimethylcyclohexylamine (DMCHA) and polystyrene, triggered by an acid in the surrounding aqueous environment. From 70 different experimental conditions, we found a scaling relationship between the drop dissolution time and initial volume with an overall scaling coefficient of 0.53. We quantitatively assessed and found a shorter dissolution time related with a decrease in pH of the aqueous phase or an increase in initial polymer concentration in the drop. Our experimental results provide a microscopic view of the SHS dissolution process from polymer drops. Examining the internal state of the drop during the dissolution revealed an in-drop phase separation behavior, resulting in a porous morphology of the final polymer particle.

    In the second part of this work, we study the effects from switching conditions on the solvent residue during the formation of polystyrene latexes induced by emulsion extraction. The extraction of DMCHA from emulsion droplets containing polystyrene was triggered by addition of an acid in the surrounding aqueous phase. We found a constant level of the solvent residue in the final polystyrene particles regardless of the trigger addition rate and trigger solution concentration. However, a decrease in the solvent residue was achieved at higher fractions of the organic dispersed phase in the emulsion or at lower extraction temperature. The solvent residue may be attributed to the formation of water-oil-water emulsion during the extraction process.

    Overall, the work presented in this thesis highlights the phase separation behavior and the link between residual solvent and trapped water. The dynamics of drop dissolution and mechanism for the presence of residual solvent reported in this work may help design SHS extraction processes for particle formation with effective approaches for reducing the residual solvent left after dissolution.

  • Subjects / Keywords
  • Graduation date
    Spring 2023
  • 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.