Comparative Gibbsian composite-system thermodynamics for confined and unconfined multicomponent multiphase systems

• Author / Creator

  Zargarzadeh, Leila

• The behavior of multiphase multicomponent systems can be well predicted by Gibbsian composite-system thermodynamics. This approach is used in this thesis to study three different systems of interest: (i) nanobubbles on a flat solid surface submerged in a liquid solution at constant temperature and liquid pressure, (ii) bubble formation, starting with a convex or a concave meniscus inside a finite cone exposed to a liquid solution at constant temperature and liquid pressure, and (iii) comparison of the polynomial equations for the osmotic virial equation and the Margules model, and their application in fitting to solid–liquid equilibrium data of different water/solute mixtures with a eutectic point. (i) A surface nanobubble has the shape of a spherical cap with a height of tens of nanometers and an anomalously high contact angle (measured through the liquid phase). The conditions for the stability of surface nanobubbles submerged in a liquid solution at constant temperature and liquid pressure are investigated by finding the conditions for equilibrium and the appropriate free energy of the system. It is assumed that on the time scale of the experiment, the bubbles are not in diffusive contact with each other or the gas phase outside the system. The changes in the concentration of the liquid phase and the surface nanobubble as it grows are both taken into account. From this investigation it is concluded that surface nanobubbles can only be stable if the liquid solution is initially supersaturated, and the contact angle is anomalously high. (ii) For a bubble starting inside a cone, with a convex or a concave meniscus (depending on the contact angle and cone apex angle), from a liquid solution at constant temperature and pressure, stability analysis has been performed by finding the conditions for equilibrium and the appropriate free energy of the system. The bubble is studied over the whole growth path: inside, pinned to the corner, and outside the finite cone. The changes in the concentration of the bulk liquid phase and the gas phase are considered as the bubble grows. For a bubble starting with a convex meniscus, a stable bubble can only form after passing an energy barrier and if the initial liquid is above a certain degree of saturation (which depends on other parameters of the system). In cases where the height of the energy barrier becomes comparable to the depth of the energy well of the stable point, and if the energy barrier is sufficiently small, bubble “formation–disappearance fluctuation” occurs. For a bubble starting with a concave meniscus, there is always at least one stable equilibrium state, even when the liquid phase is pure, and there is no initial energy barrier to be overcome. In each of the cases, the stable equilibrium may form inside, pinned, or outside the cone depending on the parameters of the system. The effect of different parameters including cone apex angle, cone half mouth radius, contact angle, total number of moles, and the initial degree of saturation, on the stability of a bubble inside a cone are investigated to present a comparative complete picture of the phenomena. (iii) The polynomial forms of the osmotic virial equation and the Margules model are compared for two-component solutions. Fitting each model to the solid–liquid equilibrium experimental data of different water/solute systems with a eutectic point shows that both models perform well in fitting the data. Fitting is done over both the ice-formation and the solute-precipitation regions. In the osmotic virial equation, the integration constant in expressing the concentration effect of the solute (that arises from the Gibbs–Duhem equation) is shown to be dependent on the osmotic viral coefficients and the relation for that is derived. The comparative approach in this study provides a big picture for each of the systems that promotes better understating, hence an ability for future design or control, of the phenomena.

• Subjects / Keywords

  • surface nanobubbles
  • interfacial nanobubbles
  • thermodynamic stability
  • resistance force
  • pinning
  • free energy
  • thermodynamic potential
  • bubble
  • liquid solution
  • cone
  • conical roughness
  • supersaturation
  • (de)wetting
  • osmotic virial equation
  • Margules equation
  • water
  • aqueous solution
  • solid–liquid equilibrium
  • thermodynamics

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-w948-pv32

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.