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Favored local structures in amorphous colloidal packings measured by microbeam X-ray diffraction

Significance Local structure and symmetry in amorphous materials and glasses may play a critical role in their formation and properties yet are notoriously hard to measure. Here, we demonstrate a direct method for measuring the proportions of polyhedra with different local point symmetries in amorphous colloidal packings, using small-volume transmission diffraction patterns. We show that local order is tuned by the interaction potential between microspheres and the method of preparation. This methodology can be readily applied to a broad range of disordered materials and packings to probe for universal features in their structure. It also has the potential to quantify local order in liquid, undercooled, and liquid–crystal systems approaching a phase transition. Local structure and symmetry are keys to understanding how a material is formed and the properties it subsequently exhibits. This applies to both crystals and amorphous and glassy materials. In the case of amorphous materials, strong links between processing and history, structure and properties have yet to be made because measuring amorphous structure remains a significant challenge. Here, we demonstrate a method to quantify proportions of the bond-orientational order of nearest neighbor clusters [Steinhardt, et al. (1983) Phys Rev B 28:784–805] in colloidal packings by statistically analyzing the angular correlations in an ensemble of scanning transmission microbeam small-angle X-ray scattering (μSAXS) patterns. We show that local order can be modulated by tuning the potential between monodisperse, spherical colloidal silica particles using salt and surfactant additives and that more pronounced order is obtained by centrifugation than sedimentation. The order in the centrifuged glasses reflects the ground state order in the dispersion at lower packing fractions. This diffraction-based method can be applied to amorphous systems across decades in length scale to connect structure to behavior in disordered systems with a range of particle interactions.