Directional Sliding Motion in Two-Dimensional Materials and Its Impact on the Resulting Hierarchical Structure

Oriented attachment (OA) is a widespread phenomenon in geochemical, biomineral, and synthetic material systems, providing a compelling approach for constructing sophisticated, complex hierarchical nanostructures in bioscience and materials science, enabling manipulation of desired properties in catalysis, magnetics, electronics, piezoelectricity, and photonics. Prior research focused on understanding the forces driving rotation point to the importance of the hydrogen bonding network to enable commensurate lattices, but few studies have addressed the lateral forces that drive uniform particle stacking. Here we present findings that reveal how pervasive these translational forces are during the OA of two-dimensional gibbsite nanoplates, and the importance of the underlying energy-structure relationship for interparticle sliding motion. We present findings that highlight the pervasive role of translational forces during the OA of two-dimensional gibbsite nanoplates and the critical influence of energy-structure relationships on interparticle sliding motion. After allowing a suspension of uniform 100 nm hexagonal gibbsite plates to settle for six months, we observed the formation of macroscopic mesocrystals. Detailed analyses using TEM, SEM, XRD, and SAXS revealed that these mesocrystals adopt a monoclinic structure, with plates stacked along the basal (0 0 1) surfaces and uniformly staggered by 32 degrees along the [0 1 0] direction. In situ liquid cell TEM further captured the sliding motion of the (0 0 1) plates along the [0 1 0] direction during self-assembly. Molecular dynamics simulations showed that sliding along the [0 1 0] direction is energetically more favorable than along the [1 0 0] direction, a preference driven by the hydrogen bond network mediated by interlayer water. These insights broaden our understanding of the forces and conditions driving OA in two-dimensional systems, providing fundamental knowledge that could inform predictive models for controlled mesocrystal synthesis.