Understanding the fate and transport of engineered and naturally-occurring nanoparticles is vital to predicting their ecological and toxicological impacts.

Oriented aggregation (OA) is a non-classical crystal growth mechanism by which uniquely shaped nanocrystals with tight size control can be produced. Primary crystallites attach with crystallographic order, leading to the formation of secondary, single crystals. Comprehensive characterization is critical for elucidating the fundamental processes of oriented aggregation. Transmission electron microscopy (TEM), cryogenic TEM, and in situ fluid cell TEM enable direct imaging of materials throughout the growth process. Correlative techniques, such as X-ray diffraction (XRD), small angle X-ray scattering (SAXS), small angle neutron scattering (SANS), dynamic light scattering (DLS), and UV-visible spectroscopy, as well as kinetic modeling, also lead to important insights. Each of these techniques has advantages and limitations; a combination of methods is required to push our understanding of OA forward.