| dc.description.abstract | Colloidal crystallization in sedimenting systems is an incompletely understood
process, where the influence of interparticle forces on the three-dimensional (3-D)
microstructure remains to be fully elucidated. This dissertation outlines work that is
intended to improve our knowledge of this subject by studying sedimentation
equilibrium and phase behavior for electrostatically repulsive systems, as well as the
interfacial crystallization of attractive depletion systems. Towards this end, several
analytical and experimental tools have been developed to explore the thermodynamic
behavior of these systems. For example, the experimental challenges necessitated the
development and implementation of the following in this work: (1) core/shell silica
particles incorporating molecular fluorophores or semiconductor nanocrystals; (2)
modification of silica particle surfaces; (3) the design of specialized sedimentation cells;
and (4) the development of a novel fluorescent intensity-based approach to quantifying
colloidal sediments. Analysis of the experimental data required the use of the following
tools: (1) location of particle centers from images; (2) deconvolution of intensity profiles using a novel Monte Carlo-type algorithm; and (3) prediction of colloidal phase
diagrams using perturbation theory.
On the basis of this work’s experimental and simulation data, it is concluded that
competing orientations of crystal grains may suppress crystallization at grain boundaries,
resulting in a non-uniform depth of the fluid/solid transition. Also, it was demonstrated
that the grain size in depletion crystals formed from quantum dot-coated silica particles
can be increased by localized annealing with the confocal microscope’s laser.
Additional findings include the ability of the intensity-based approach to measure
interparticle forces in colloidal sediments, as well as the inability to use perturbation
theory to predict two-dimensional colloidal fluid/solid transitions. While significant
progress has been achieved, work on 3-D imaging of colloidal depletion crystals in a
refractive index-match medium is ongoing.
This work improves our understanding of 3-D colloidal crystallization at
interfaces, as well as provides new tools for future research. Also, this work
demonstrates a potential route for zone refining of colloidal crystals, a technique that
may be important in the search for low-defect 3-D arrays that can be used as templates
for photonic bandgap materials. | en |
