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Multicomponent, Multiphase Thermodynamics with Interfacial Curvature

  • Author / Creator
    Shardt, Nadia
  • The interface between two phases—for example, a liquid and a vapor phase—influences the properties of the phases it separates. When the interface is flat, the phase properties of both single- and multicomponent systems can be reliably predicted by applying well-established thermodynamic principles. When the interface is curved, phase properties change according to the extent of the curvature, and this curvature-dependent effect has been studied extensively in single-component systems. This thesis investigates the intersection where multicomponent, multiphase systems contain interfacial curvature. Contributions are made to three questions at this intersection: (1) how does the surface tension of a multicomponent mixture vary as a function of composition and temperature? (2) how does the vapor–liquid phase diagram of a multicomponent system change when there is a curved interface between the vapor and liquid phases? and (3) how does the contact angle of a liquid drop change when it is on a chemically heterogeneous or physically rough solid phase compared to a homogeneous, smooth solid? Considering the first question, a new equation is developed to predict the surface tension of multicomponent liquid mixtures, and it is validated against experimental data for a wide range of temperatures, pressures, and mixture types (those containing one supercritical compound (e.g., carbon dioxide) and those containing two subcritical compounds (e.g., organic and aqueous mixtures)). In pursuing the second and third questions, the postulates of Gibbsian composite-system thermodynamics—a mathematical framework that describes relationships between energy and the properties of matter—are applied to each studied system. For calculating the phase diagrams of multicomponent systems with nanoscale interfacial curvature, an activity-coefficient model is developed and applied to both ideal and nonideal systems; the newly-developed surface tension model is incorporated into this system of equations. For describing contact angle, a rigorous mathematical approach is presented, which demonstrates that the properties at the circumference of the liquid drop determine the contact angle—that is, a line fraction for a chemically heterogeneous surface and a line roughness for a physically rough surface. As a whole, this thesis develops fundamental mathematical equations to quantify the effect of interfacial curvature on the properties of multicomponent, multiphase systems for use in the multitude of applications where curved interfaces are present, such as atmospheric physics, medicine, catalysis, and soft matter nanotechnology.

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  • Graduation date
    Fall 2019
  • Type of Item
  • Degree
    Doctor of Philosophy
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