(552c) Structures and Dynamics of Boehmite Crystal Aggregation

While aggregation kinetics and resultant aggregate structures for spherical colloids have been studied extensively, such studies for sharp-edged non-spherical particles have been relatively unexplored. We studied the structure and dynamics of aggregation for rhombohedral boehmite crystals as a function of solution pH and ionic strength based on dynamic light scattering (DLS), combined with cryo-transmission electron microscope. The coagulation rate constants obtained from DLS during the early stages of aggregation are found to span seven orders of magnitude and cross both the reaction-limited and diffusion-limited regimes. A simple scaling for van der Waals, electrostatic, and hydrodynamic interactions combined with rotational/translational diffusivities of irregular particle shapes provides qualitative understanding of the effects of orientation for the irregular-shaped colloids on the early stages of aggregation. Unusually high fractal dimensions of the aggregates are observed in the diffusion-limited aggregation regime, which can be qualitatively explained by a simple geometric parameter (i.e., a contact area between the particles) based on Monte Carlo simulations.