Although orientation-dependent forces governing crystallization by particle attachment have been reported, their scaling with particle anisotropy and solution chemistry remains unknown. Accordingly, the collective dynamics of systems exhibiting oriented attachment remain difficult to predict, particularly for non-spherical particles. In this context, we investigated the structure and dynamics of boehmite aggregation as a function of solution pH and ionic strength. Cryogenic transmission electron microscopy showed that boehmite platelets assemble by oriented attachment on (010) planes. The coagulation rate constants obtained from dynamic light scattering span both the reaction-limited and diffusion-limited regimes. We use simple scaling arguments, calculations of stability ratios, and rotational/translational diffusivities of irregular particle shapes to rationalize the effects of orientation on the early stages of aggregation. Using Monte Carlo simulations, we found that a nanoscale geometric parameter, namely the contact area between two attaching platelets, has a determining impact on the emerging macroscale aggregates and explains their unusually high fractal dimensions.

Structure and collective dynamics of boehmite-oriented aggregation

2019 Spring National Meeting

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