Browsing by Subject "Colloidal crystals"

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    Modeling of transport processes during solution, melt and colloidal crystal growth.
    (2008-08) Gasperino, David Joseph.
    In this thesis, numerical models are developed and applied to study systems used for the growth of crystals from both solution and the melt. Additionally, numerical models are employed to study the convective self-assembly of microspheres within solution. Solution crystal growth can be visualized in real-time through the application of atomic force microscopy (AFM) within a fluid cell. We apply a three-dimensional finite element method on a parallel supercomputer to determine the continuum transport of momentum and mass in an AFM fluid cell during crystal growth, using data acquired from calcium oxalate monohydrate crystal growth measurements as a comparison. Simulations quantify mass transfer resistances to crystal growth inherent to the fluid cell geometry, and examine influences on growth via high-frequency cantilever oscillations. The melt growth of single crystal cadmium zinc telluride (CZT), a high-value crystal used in radiation detectors, has posed a serious challenge for crystal growers for over three decades. We employ a two-dimensional finite volume method to simulate CZT growth in a vertical Bridgman furnace used by our collaborators at Pacific Northwest National Laboratories. Models couple the continuum transport of mass, momentum and radiation, and track the interface shape between the melt and crystal. Results provide insight into the thermal behavior of two crucibles to be used for CZT growth by our collaborators. Three-dimensional computations of steady flows directed toward the (1 1 1) plane of a face-centered cubic (fcc) packing of microspheres are carried out to assess the convective steering hypothesis, which posits that solvent flow could play a role in the assembly of colloidal crystals. The computations clearly show the kinematics of flows into and through the packing and clarify the influences of fluid inertia and particle arrangement. Results from the computations accurately describe the outcome of macroscopic experiments.
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    Understanding DNA Electrophoresis in Colloidal Crystals
    (2014-08) King, Scott
    The electrophoretic separation of DNA (deoxyribose nucleic acid) has been a target of engineering and optimization since its inception. In the following pages, I describe an engineering investigation into the physics of DNA separation in colloidal crystals. Colloidal crystals are formed through self-assembly of micron-sized spheres, suspended as a colloidal suspension. In this work, we follow the pioneering separation work of Zeng and Harrison, seeking to better understand the properties that allow for the observed enhanced separations of small, <1 kilo base-pair (kbp) DNA and large (>10 kbp) DNA. I demonstrate some key insights required to fabricate these devices, then move on to evaluating their performance. In the first section I tackle the quality of the crystal and its potential effects on separation performance. In the second section, I attempt to explain the order of magnitude better separation behavior between agarose gels and colloidal crystals by evaluating the mobility regimes for large DNA. At the end of this work, I have included a discussion on the future place of colloidal crystals as a separation medium.