Functional materials for destabilizing and stabilizing emulsions and underlying interfacial interaction mechanisms

• Author / Creator

  Mao, Xiaohui

• Oil related issues such as oil/water emulsions are critical challenging issues in a wide range of engineering processes and have caused negative effects to economy, environment, and ecology. Despite much effort devoted to this area, the developed materials remain many limitations. For example, the traditional materials for breaking the asphaltenes stabilized emulsions are usually amphiphilic polymers that may further stabilize the emulsion at high dosage. In the oil spill treatment and destabilization of surfactant stabilized emulsions, the developed materials are usually functionalized by polymers via complicated methods. The material synthesized via a simple strategy using small molecules has rarely been reported. Besides, the understanding of underlying mechanisms needs to be improved, especially in the aspect of direct force measurement of interactions between emulsified droplets in emulsion, which plays an important role in predicting and altering the stability of emulsions.
  In this project, a novel functional material with superhydrophilic polyelectrolyte has been developed to destabilize asphaltenes-stabilized emulsion, and the scalable materials functionalized with small molecules have been synthesized via a simple and facile method for oil absorption, oil/water separation and demulsification. The atomic force microscope (AFM) is employed to study the interactions between water/oil droplet and as-prepared materials, and the interactions between two water or oil droplets with interfacially active particles to elucidate the destabilization and stabilization mechanisms of emulsion.
  In the first work, novel core-shell microspheres consisting of magnetic core and superhydrophilic zwitterionic polyelectrolyte shell have been developed to break asphaltenes stabilized water-in-oil (W/O) emulsion and to release water from the emulsion with the assistance of external magnetic field. In the study of interactions and mechanism, AFM force measurement reveals strong attraction between the polyelectrolyte and water droplet surrounded by interfacially absorbed asphaltenes in oil. Besides, the addition of as-synthesized core-shell microspheres increase the water-oil interfacial tension (IFT). Also, the result of quartz crystal microbalance with dissipation (QCMD) test shows that asphaltenes can adsorb on the polyelectrolyte.
  In the second work, fiber-based hydrophobic and oleophilic materials are synthesized via a facile and scalable method using a small molecule, γ-mercaptopropyldi(trimethylsiloxy)methylsilane (MD(SH)M). The MD(SH)M-functionalized materials can effectively absorb five types of oil spills from water, separate water from the mixture with high-density/low-density oil and destabilize asphaltenes/surfactants stabilized emulsions. The mechanism is studied using adhesion force measurement and AFM force measurement and is found to be related to the hydrophobicity and oleophilicity of as-prepread materials, as well as the hydrophobic interaction between MD(SH)M and oil droplets in aqueous phase.
  In the third work, the Pickering emulsions formed by oil/water mixture under pH 2, 4, 9 and 11 with bilayer oleic acid coated Fe3O4 nanoparticles (Fe3O4@2OA NPs) are characterized using microscope imaging, zeta potential, IFT and AFM force measurement. W/O emulsion is formed at pH 2 and 4, and its stabilization mechanism is mainly governed by the formation of steric barrier of the confined particle layer (with Fe3O4@2OA NPs and aggregates). At pH 9 and 11, oil-in-water (O/W) emulsion is formed, and its stabilization mechanism is mainly due to relatively low IFT, strong electrostatic repulsion from negatively charged carboxyl groups, and steric repulsion from the confined nanoparticles and their aggregates.
  In the fourth work, the small molecule MD(SH)M is used to prepare slippery surface that is independent of complex micro-/nano-scale surface structures and conventional infused lubricant oils. The as-prepared MD(SH)M surfaces allow facile transport of bubbles in aqueous media and water drops in oil, as well as facilitate the self-assembly of nanoparticles from their aqueous suspensions. The MD(SH)M slippery surfaces have lower surface energy and contact angle hysteresis as compared to conventional lubricant liquid-infused slippery surfaces, which allows the three-phase contact line to move more freely and accounts for the higher moving velocity of bubbles/drops under the same test condition.
  In all, this project has developed novel superhydrophilic demulsifier for asphaltenes stabilized emulsion and paved a new way to separate oil and water using small molecules. Our work points out a new path using polyelectrolytes and suitable small molecules to effectively solve the oil/water emulsion issues and provides useful insights into the interaction forces of Pickering emulsions stabilized by stimuli-responsive interface-active particles, which has great significance and potential applications in many engineering processes.

• Subjects / Keywords

  • surface force
  • atomic force microscope
  • demulsification
  • emulsions

• Graduation date

  Fall 2021

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-96zz-1p26

• 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.