Light scattering at the nonequilibrium crystal melt interface: Salol and succinonitrile.
Item
-
Title
-
Light scattering at the nonequilibrium crystal melt interface: Salol and succinonitrile.
-
Identifier
-
AAI9207139
-
identifier
-
9207139
-
Creator
-
Williams, Lloyd Melvyn.
-
Contributor
-
Adviser: Herman Cummins
-
Date
-
1991
-
Language
-
English
-
Publisher
-
City University of New York.
-
Subject
-
Physics, Optics | Physics, Condensed Matter
-
Abstract
-
The phenomenon of diffusive dynamic light scattering at the crystal-melt interface has been investigated in salol and succinonitrile. The origin of this phenomena is a matter of some controversy which this thesis will attempt to resolve. Of the several models that have been proposed to explain the phenomenon, the microbubble model (Cummins et al. Solid State Communications 60, p857 1986) and the mesophase model proposed by the ETH Zurich group of J. Bilgram and co-workers (Boni et al. Phys. Rev. A 28, p2953 1983) are the only two explanations still consistent with most of the observed properties of the scattering.;In the experiments on salol the scattering has been observed for 14 days. The hydrodynamic radius deduced from intensity correlation data increased continuously from {dollar}\sim{dollar}1 to 100 {dollar}\mu{dollar}m. When the scattering layer was trapped by the advancing crystal front, microscopic observation revealed bubbles as inclusions whose size agreed with the light scattering values.;In the experiments on succinonitrile the angular dependence of the scattered light was investigated. In the mesophase model the light is scattered by density fluctuations. The angular dependence of light scattered by density fluctuation is described by the Ornstein-Zernike form I(q) = I{dollar}\sb0{dollar}(1 + q{dollar}\sp2\xi\sp2{dollar}). However, light scattered by bubbles can be modeled using the appropriate Mie function for the problem. The data was found to be incompatible with the Ornstein-Zernike form; however, it could be reasonably well fit by Mie theory.;The behavior of the onset of the scattering was also investigated, and it was found that the product R{dollar}\sb0{dollar}t{dollar}\sb0{dollar}v{dollar}\sb{lcub}\rm g{rcub}\sp2{dollar} was a constant, where R{dollar}\sb0{dollar} is the onset radius, t{dollar}\sb0{dollar} is the onset time, and v{dollar}\sb{lcub}\rm g{rcub}{dollar} is the crystal growth velocity. This was consistent with the analysis of Mesquita et al.(1987) in which the onset of the scattering was modeled by considering the rate of buildup of dissolved gas at the advancing crystal-melt interface.;The gases dissolved in our samples of succinonitrile were identified by mass spectroscopy and found to have a composition similar to air.
-
Type
-
dissertation
-
Source
-
PQT Legacy CUNY.xlsx
-
degree
-
Ph.D.
