(552c) Structures and Dynamics of Boehmite Crystal Aggregation

Authors: 
Chun, J., Pacific Northwest National Laboratory
Nakouzi, E., Pacific Northwest National Laboratory
Soltis, J., Pacific Northwest National Laboratory
Legg, B., Pacific Northwest National Laboratory
Schenter, G. K., Pacific Northwest National Laboratory
Zhang, X., Pacific Northwest National Laboratory
Graham, T. R., Voiland School of Chemical Engineering and Bioengineering, Washington State University
Rosso, K., Pacific Northwest National Laboratory
Anovitz, L., Oak Ridge National Laboratory
De Yoreo, J. J., Pacific Northwest National Laboratory
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.