Bradley Dice

Computational materials science work performed in the O'Hern research group at Yale University, part of the Center for Research on Interface Structures and Phenomena (CRISP).

Abstract: The likelihood that an undercooled liquid vitrifies or crystallizes depends on the cooling rate R. The critical cooling rate Rc, below which the liquid crystallizes upon cooling, characterizes the glass-forming ability (GFA) of the system. While pure metals are typically poor glass formers with Rc >… Show more

Computational materials science work performed in the O'Hern research group at Yale University, part of the Center for Research on Interface Structures and Phenomena (CRISP).

Abstract: The likelihood that an undercooled liquid vitrifies or crystallizes depends on the cooling rate R. The critical cooling rate Rc, below which the liquid crystallizes upon cooling, characterizes the glass-forming ability (GFA) of the system. While pure metals are typically poor glass formers with Rc > 1012 K/s, specific multi-component alloys can form bulk metallic glasses (BMGs) even at cooling rates below R ∼ 1 K/s. Conventional wisdom asserts that metal alloys with three or more components are better glass formers (with smaller Rc) than binary alloys. However, there is currently no theoretical framework that provides quantitative predictions for Rc for multi-component alloys. In this manuscript, we perform simulations of ternary hard-sphere systems, which have been shown to be accurate models for the glass-forming ability of BMGs, to understand the roles of geometric frustration and demixing in determining Rc. Specifically, we compress ternary hard sphere mixtures into jammed packings and measure the critical compression rate, below which the system crystallizes, as a function of the diameter ratios σB/σA and σC/σA and number fractions xA, xB, and xC. We find two distinct regimes for the GFA in parameter space for ternary hard spheres. When the diameter ratios are close to 1, such that the largest (A) and smallest (C) species are well-mixed, the GFA of ternary systems is no better than that of the optimal binary glass former. However, when σC/σA <= 0.8 is below the demixing threshold for binary systems, adding a third component B with σC < σB < σA increases the GFA of the system by preventing demixing of A and C. Analysis of the available data from experimental studies indicates that most ternary BMGs are below the binary demixing threshold with σC/σA < 0.8. Show less

Physics research performed in collaboration with Dr. Patrick Bunton of William Jewell College and the de Wit group at the Free University of Brussels.

Abstract: We study the spatio-temporal evolution of the viscosity field during stable and unstable radial flows of glycerol-water solutions in a horizontal Hele-Shaw cell where a localized temperature gradient is imposed. The viscosity field is reconstructed from the measurement of the fluorescence emitted by a viscosity-sensitive… Show more

Physics research performed in collaboration with Dr. Patrick Bunton of William Jewell College and the de Wit group at the Free University of Brussels.

Abstract: We study the spatio-temporal evolution of the viscosity field during stable and unstable radial flows of glycerol-water solutions in a horizontal Hele-Shaw cell where a localized temperature gradient is imposed. The viscosity field is reconstructed from the measurement of the fluorescence emitted by a viscosity-sensitive molecular probe (Auramine O). For an immiscible flow, the viscosity and temperature fields are obtained accurately. For miscible displacements, we show how the interplay between the viscosity changes of both fluids and the variation of the fluid thickness in the gap prevents obtaining strict quantitative reconstruction of the viscosity field. We explain how the reconstructed viscosity field can nevertheless be interpreted to obtain information about the fluid thickness and the local viscosity and temperature. Show less