Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
2 results
Search Results
Item Hot and Cold Water as a Supercritical Solvent(2012) Fuentevilla, Daphne Anne; Anisimov, Mikhail A; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation addresses the anomalous properties of water at high temperatures near the vapor-liquid critical point and at low temperatures in the supercooled liquid region. The first part of the dissertation is concerned with the concentration dependence of the critical temperature, density, and pressure of an aqueous sodium chloride solution. Because of the practical importance of an accurate knowledge of critical parameters for industrial, geochemical, and biological applications, an empirical equation for the critical locus of aqueous sodium chloride solutions was adopted in 1999 by the International Association for the Properties of Water and Steam (IAPWS) as a guideline. However, since this original Guideline on the Critical Locus of Aqueous Solutions of Sodium Chloride was developed, two new theoretical developments occurred, motivating the first part of this dissertation. Here, I present a theory-based formulation for the critical parameters of aqueous sodium chloride solutions as a proposed replacement for the empirical formulation currently in use. This formulation has been published in the International Journal of Thermophysics and recommended by the Executive Committee of IAPWS for adoption as a Revised Guideline on the Critical Locus of Aqueous Solutions of Sodium Chloride. The second part of the dissertation addresses a new concept, considering cold water as a supercritical solvent. Based on the idea of a second, liquid-liquid, critical point in supercooled water, we explore the possibility of supercooled water as a novel supercooled solvent through the thermodynamics of critical phenomena. In 2006, I published a Physical Review letter presenting a parametric scaled equation of state for supercooled-water. Further developments based on this work led to a phenomenological mean-field "two-state" model, clarifying the nature of the phase separation in a polyamorphic single-component liquid. In this dissertation, I modify this two-state model to incorporate solutes. Critical lines emanating from the pure-water critical point show how even small additions of solute may significantly affect the thermodynamic properties and phase behavior of supercooled aqueous solutions. Some solutes, such as glycerol, can prevent spontaneous crystallization, thus making liquid-liquid separation in supercooled water experimentally accessible. This work will help in resolving the question on liquid polyamorphism in supercooled water.Item A Scaled Equation of State for the Liquid-Liquid Critical Point in Supercooled Water(2007-09-14) Fuentevilla, Daphne Anne; Anisimov, Mikhail A; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The second-critical-point scenario is one of the most popular explanations for the anomalous behavior of supercooled liquid water. According to this scenario, liquid water at ambient conditions is a "supercritical" ?uid that separates into two types of liquid water in the supercooled region. However, experimental confirmation is challenging. In this work we developed a scaled parametric equation of state, based on the principle of critical-point universality, to examine the second-critical-point scenario from a new direction. The equation of state, built on the growing evidence for liquid-liquid water separation, is universal in terms of theoretical scaling fields and belongs to the Ising-model universality class. The theoretical scaling fields are postulated to be analytical combinations of the physical fields, pressure and temperature. The equation of state enables us to accurately locate the "Widom line" (locus of stability minima) and determine that the critical pressure is considerably lower than predicted by computer simulations.