Year of Publication

2007

Document Type

Dissertation

College

Engineering

Department

Mechanical Engineering

First Advisor

M. Pinar Mengüç

Abstract

Light scattering is a powerful characterization tool for determining shape, size, and size distribution of fine particles, as well as complex, irregular structures of their aggregates. Small angle static light scattering and elliptically polarized light scattering techniques produce accurate results and provide real time, non-intrusive, and in-situ observations on prevailing process conditions in three-dimensional systems. As such, they complement conventional characterization tools such as SEM and TEM which have their known disadvantages and limitations. In this study, we provide a thorough light scattering analysis of colloidal tungsten trioxide (WO3) nanoparticles in the shape of irregular nanospheres and cylindrical nanowires, and of the resulting aggregate morphologies. Aggregation characteristics as a function of primary particle geometry, aspect ratio of nanowires, and the change in dispersion stability in various polar solvents without the use of dispersants are monitored over different time scales and are described using the concepts of fractal theory. Using forward scattered intensities, sedimentation rates as a result of electrolyte addition and particle concentration at low solution pH are quantified, in contrast to widely reported visual observations, and are related to the aggregate structure in the dispersed phase. For nanowires of high aspect ratios, when aggregate structures cannot directly be inferred from measurements, an analytical and a quasiexperimental method are used.

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