Interfacial Structure, Interparticle Forces and Assembly Dynamics During Crystallization by Particle Attachment

Crystallization by particle attachment (CPA) to form hierarchical structures is a common phenomenon and a promising approach to synthesizing functional materials. CPA exhibits diverse styles ranging from oriented attachment (OA), by which individual nanocrystals of the same phase attach with crystallographic coalignment, to mis-oriented aggregation of nanocrystals with disparate phases followed by coarsening to single-phase, ordered structures. CPA leads to remarkable morphological outcomes, including formation of tetrapods, chains and sheets, highly branched nanowires, and self-similar 3D mesocrystals. Moreover, CPA has now been widely observed in semiconductors, metals, silicates, oxides, fluorides, carbonates, organic compounds, peptides, and proteins. While descriptions of CPA must share a commonality with continuum-based DLVO-type theories for simple isotropic colloids, nanocrystals present additional complexities, including face-specificity of dielectric properties, inherent diopolar interactions, structured nanoscale interfaces, solvent-responses at a length scale comparable to particle size, and the impact of organic ligands often used to stabilize nanoparticles on the interparticle potentials. Macromolecular systems add another level of complexity due to their electrostatic patchiness and specific interactions via side chain chemistry. To understand the relationship between interfacial structure, interparticle forces and assembly dynamics, as well as the role of organic ligands and the properties of macromolecules, we are investigating CPA in a range of systems, including noble metals, metal oxides, peptides, and proteins, using a combination of in situ TEM, in situ AFM, and molecular modeling. In this talk I will focus on, 1) the effects of organic ligands in both driving CPA and creating unique crystal morphologies, and 2) the distinct behavior exhibited by proteins, due to their uniform, but anisotropic, dimensions and charge distributions. The results shed light on the mechanisms by which CPA progresses, the interaction potentials that drive the process, and the role of interfacial structure in defining those potentials.