Condensed Matter Seminar: Mechanism guided crystal growth: from molecular mechanisms to mature crystals with designed morphologies

One of the major challenges in organic crystalline materials is translating molecular-level understanding of crystal growth mechanisms into the rational design of crystals with targeted properties. We demonstrate that by elucidating growth mechanisms and kinetics, crystallization pathways can be deliberately manipulated to achieve predictive control over crystal geometry, structure, and function.

Previously, we studied birefringent theophylline crystals and shown that driving crystallization into the classical growth mode, where crystals grow molecule-by-molecule via two-dimensional nucleation and layer spreading, enables precise control over crystal structure, shape, and dimensions. By tailoring growth conditions, we achieve polymorph selectivity among neat and hydrated forms and direct morphology toward either one-dimensional needle-like crystals or two-dimensional.

Currently, we extend these insights to morphology-sensitive energetic materials, focusing on hexanitrostilbene (HNS), a highly thermostable compound widely used in aerospace and deep-well applications. Conventional synthesis produces irregular needle- or plate-like crystals that increase mechanical sensitivity and hinder processing. Creating a safety challenge. In contrast, our mechanistically guided, surfactant-free crystallization strategy enables the reproducible formation of dense, spherical HNS particles with narrow size distribution, minimal aggregation, and preserved phase purity. Multimodal characterization (optical microscopy, SEM, AFM, TEM, and XRD) confirms their structural integrity and morphological uniformity.

Together, these results envision a general and transferable framework for rational crystal engineering, demonstrating that mechanistic insight into nucleation and growth enables precise, predictive control over crystal morphology in functional materials.