Gravity enables selfâassembly
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jats:titleAbstract</jats:title>jats:sec<jats:label />jats:pCrystallization of granular assemblies has broad implications for rapid and scalable creation of architected materials with applications ranging from structural materials to microarchitected battery electrodes. While significant advances have been made in understanding colloidal selfâassembly at nano to micro scale, the governing mechanisms for organization of dry assemblies of hard spheres remain unclear. Here, we investigate crystallization of monoâsize hard spheres with and without imposed vibration. Using Xâray computed tomographic analysis coupled with discreteâelement simulations, we unravel the roles of gravity and imposed vibration on the threeâdimensional selfâassembly of the dry spheres. We use these insights to introduce gravityâmediated epitaxial crystal growth with slow pouring of balls on seeding templates. Contrary to vibrationâinduced crystallization, this method can form large single crystals with both closeâpacked and rather surprisingly, noncloseâpacked metastable particle arrangements. Our results provide insight for the scalable manufacture of defectâfree granular assemblies that can be used as spaceâholding templates to manufacture cellular materials, such as inverse opals and other related topologies.</jats:p></jats:sec>jats:secjats:titleKey points</jats:title>jats:p<jats:list list-type="bullet"> jats:list-itemjats:pSelfâassembly of hard spheres is a critical step for the scalable manufacture of microâarchitected solids.</jats:p></jats:list-item> jats:list-itemjats:pVia a combination of vibration experiments, 3D Xâray tomographic observations, and simulations, we elucidate the critical role of gravity in the selfâassembly of hard spheres.</jats:p></jats:list-item> jats:list-itemjats:pWe design seeding templates that can not only induce the selfâassembly into stable closeâpacked crystal structures but also rather counterintuitively into metastable single crystal structures.</jats:p></jats:list-item> </jats:list></jats:p></jats:sec>
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2698-6248