Homogeneous nucleation theory

Author: McClurg, Richard Beatty

Year: 1997

Degree: Dissertation (Ph.D.)

Advisors: Goddard, William A., III; Flagan, Richard C.

Committee Members: Flagan, Richard C.; Goddard, William A., III

Option: Chemical Engineering

DOI: 10.7907/Z011-9767

Abstract

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This thesis is composed of a brief preface followed by six chapters addressing various aspects of homogeneous nucleation theory. In the preface, I motivate the need for improved theoretical approaches to resolve the discrepancies between current theory and experiment. The remaining chapters are collected research papers which are in print, in press, or to be submitted as of the writing of the thesis. They were written in collaboration with one or both of my advisors. In Chapter 2, we review current nucleation theories in a statistical mechanical framework. This framework allows us to identify the errors of the various models and to point out internal inconsistencies in some of them. In Chapters 3 and 4, we develop methods to calculate the partition function and thermodynamic properties for noble gas clusters. The methods allow us to describe the asymptotic approach of cluster properties toward the bulk limit with increasing cluster size and to calculate the nucleation rate for supersaturated noble gas vapors. We then apply the methods to the homogeneous nucleation of condensed mercury from a supersaturated vapor in Chapter 5. Chapters 6 and 7 contain portions of the theoretical groundwork needed to extend atomistic nucleation theories to molecular systems. Chapter 6 is a development of a one-dimensional hindered rotor partition function. It sets the stage for the two and three-dimensional hindered rotor partition functions needed to model molecular solids. In Chapter 7 we construct a model for the charge distribution of [...]. We chose this icosahedral molecule as an ideal plastic crystalline substances. The plastic crystals are solids with translational symmetry, but having weak orientational symmetry due largely to their highly symmetric molecular charge distributions. Thus, plastic crystals are ideal hindered rotors in multiple dimensions. I conclude the thesis with some brief comments on my assertion that molecules which form plastic crystals will provide a fruitful common ground for theoretical and experimental investigations of homogeneous nucleation phenomena.

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