Understanding the mechanism for crystallization pathway selection remains a significant challenge as none of the existing models is able to capture the full complexity of interatomic and many-body collective interactions driving nucleation and assembly processes. The central difficulty lies in the description of the correlated fluctuation dynamics in multicomponent solution central to the understanding of the mechanism for the formation of metastable density fluctuations during nucleation and subsequent crystal growth. Coupling the theory of inhomogeneous complex fluids to quantum mechanical descriptions of short-range forces can potentially provide a first-principles framework for studying complex non-equilibrium processes, including heterogeneous nucleation and particle-based crystallization. The combination of such coupled plane-wave / classical DFT approach with in situ TEM and AFM characterization of crystallization processes reveals that interfacial correlated solvent dynamics plays a central role in crystallization pathway selection. Simulations indicate that adjusting the relative contribution of interfacial ion correlation interactions into the total chemical potential of precursor species by varying solution pH can induce the transition between classical monomer addition and particle-based crystallization. Similarly, the relative strength of face specific ion correlation interactions and isotropic long-range van der Waals interactions can define the pH window for crystallization via oriented attachment or random aggregation of the particles. Detailed experimental and theoretical studies of TiO<sub>2</sub> and ZnO interparticle forces indicate that at 0.5-2 nm separations face specific interactions include repulsive hydration, attractive ion correlation and short-range particle-particle van der Waals forces. During the oriented attachment process these interactions promote fine adjustment of particle mutual orientation while in the solvent separated state to maximize the attractive force, facilitate solvent expulsion from the interparticle gap and create the conditions for the diffusive jump to contact driven by chemical forces. In contrast, during the coalescence process the strength of the attractive interactions between the misaligned particle may be insufficient to overcome hydration repulsion. The particles may remain separated by 0.5 nm and a bridge is formed between them to initiate contact.

Understanding the driving forces for particle-based crystallization through theory and simulations

2019 Spring National Meeting

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