A comprehensive solvation theory for colloidal forces with application to both neutral and charged systems
Frink, Laura Jane Douglas
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Permalink
https://hdl.handle.net/2142/22581
Description
Title
A comprehensive solvation theory for colloidal forces with application to both neutral and charged systems
Author(s)
Frink, Laura Jane Douglas
Issue Date
1995
Doctoral Committee Chair(s)
van Swol, Frank
Department of Study
Chemical and Biomolecular Engineering
Discipline
Chemical and Biomolecular Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Engineering, Materials Science
Language
eng
Abstract
This thesis presents a new framework for studying colloidal forces. This framework combines accurate density functional theories for calculating potentials of mean force (or solvation potentials) with McMillian-Mayer theory. Furthermore, combined density functional theory and simulation methods were developed to study solvation transitions and crystallization in neutral solvation controlled systems. These calculations highlighted the independent roles of a mechanical osmotic stress and the solvent chemical potential in manipulating the solvation state of (bio)colloidal systems. While many experimental systems do not rigorously treat these variables as independent, such experiments have been proposed. In addition to studying the general features of solvation control in the parallel cube model, some specific molecular features of the macromolecules have been considered. Randomly rough surfaces with the characteristic roughness on the order of the solvent molecule diameter are shown to destroy solvation structuring. In contrast, periodic roughness commensurate with the size of the solvent molecules stabilizes solvation effects as the solvent fills in the gaps making the surface effectively smooth. Finally, charged systems were considered with the specific goal of applying the new colloidal force framework to a study of the swelling of vermiculite clays. In contrast with the classical theories, the ensemble of the solvation framework provides for chemical equilibrium between a confined solution and a bulk solution in addition to mechanical equilibrium for the clay particles. A weak-gas density functional theory confirmed the existence of a long range attraction with electrostatic origins, and demonstrated that trends similar to experimental results could be predicted. It is important to note that electrostatics can be thought of as a subset of the solvation theory, and ions should be treated on an equal footing with the solvent when calculating solvation potentials. In contrast, direct forces (e.g. van der Waals) forces are not part of the solvation potential, but rather are added to the solvation potential when assessing the total interaction between two colloids through a charged medium.
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