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Date of Award
Physics and Astronomy
Modeling the dynamics of interacting many-particle systems is one of the central challenges at the forefront of condensed matter physics. When systems of interacting particles are driven out of equilibrium, complex emergent behaviors can arise that are difficult to predict from their individual properties. In this work, we model two such dynamic many-particle systems. The first is a nanocomposite of conductive CrO2and insulating Cr2O3 nanoparticles. We numerically model the nanoparticles as hard spherocylinders, systems of which are compressed into dense, disordered, packings via the mechanical contraction method, with various volume fractions of conductive CrO2. We then analyze the resulting ensembles of these nanocomposites to identify their critical percolation properties through a finite size scaling analysis. We use a randomly walking ”blind ant” approach to calculate the conductivity of the nanocomposite and obtain the conductivity critical exponent of the nanocomposite system, which agrees with experimental measurements. Intriguingly, the calculated percolation threshold we obtained,pc= 0.312±0.002, is near (within numerical errors) those found previously in two other systems, disordered jammed spheres, and simple cubic lattice.The second type of system we model the evolution of is embedded grains in two dimensional (2D) crystals. We model 2D materials with the phase field crystal (PFC) model,which captures both atomic spatial resolution and slow diffusive dynamics, allowing for precise mapping of defect structures around evolving grain boundaries. We apply the Cahn-Taylor formulation of grain boundary motion to show that the normal motion of a shrinking embedded grain boundary couples to the tangential motion of atoms along the boundary,resulting in a net rotation of the grain as it changes size. Furthermore, we show that a more complex two component system such as hexagonal boron nitride (h-BN) exhibits a dual mode behavior of grain rotation, where the bonding energy difference between different atomic species results in competing rotations in opposite directions for binary embedded grains. This highlights the role played by the lattice inversion symmetry breaking in binary or multi-component materials as compared to single-component materials. The potential implications for processing techniques used to produce large crystals of 2D materials are also discussed.
Waters, Brendon, "Multiscale Modeling Of Dynamic Particle Systems" (2021). Wayne State University Dissertations. 3557.