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Coarsening and grain boundary dynamics in a two-dimensional colloidal hard sphere system

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Understanding grain growth in polycrystalline materials is crucial in metallurgy to enable tuning the mechanical properties of metals and alloys. Also from a fundamental point of view it is interesting to study grain growth dynamics as a non-equilibrium ordering process [1]. From an experimental point of view, colloidal polycrystalline materials are very convenient model systems to study grain growth, since they can be imaged by means of simple optical microscopy at single particle resolution and high frame rate [2]. This enables bridging the time and length scales between the single particle and grain size level and obtain a comprehensive structural and dynamical picture of grain growth in a single experiment.

In this work we develop a two-dimensional colloidal hard sphere system and characterise its equilibrium structure by comparing the radial distribution functions and experimentally determined contact values to a recent fundamental measure theory for hard disks [2]. This system is then used to study the grain growth process of a polycrystalline monolayer of colloidal hard spheres after a quench into the crystalline state. The time-evolution of the orientational order is studied and we find strong orientational ordering. The orientational correlation function exhibits dynamic scaling [3] and the associated correlation length increases as a power law in time, where the exponent is lower than expected for an isotropic curvature driven growth [4]. We find that the annihilation of large angle grain boundaries is the main coarsening mechanism, which is supported by the linear decay in the orientational correlation function at intermediate distances [1, 4]. We finally show that the migration of large angle grain boundaries is caused by small and local particle displacements, thereby gradually changing their local orientation. Interestingly, the displacements are found to correspond to the minimum displacement vectors obtained by geometrically mapping the expanding grain onto the shrinking grain.

This talk is part of the BPI Seminar Series series.

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