Materials World Network (MWN) for Particle-mediated Control Over Crystallization: From the Pre-nucleation Stage to the Final Crystal

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A Materials World Network (MWN) will be formed to investigate mechanisms of particle-mediated crystallization through which mesocrystals — crystals structured on the mesoscale — are created. In biomineral systems, mes-ocrystal formation is a widespread phenomenon mediated by biomolecules and leading to the hierarchical organization commonly associated with these materials. Our ultimate goal is a mechanistic understanding of this process and a set of principles to guide biomimetic strat-egies to create hierarchically organized materials (e.g. bioceramics, photonic solids, energy harvesting materials). The value added by the international collaboration is that it facilitates this goal by combining expertise in chemistry and growth of mesocrystals with capabilities in high-resolution in situ imaging, measurement of interactions, determination of structure, and modeling and simulation from the atomic to mesoscale. Using the calcium carbonate, iron oxide and calcium-silicate hydrate (C-S-H) systems combined with polymers, the project will pursue three thrusts, structured around the key scientific questions: Thrust 1: The pre-nucleation stage, nucleation of primary nanoparticles and intermediate phases - The nature of pre-nucleation clusters will be determined using ion potential measurements, titration and ultracentrifugation. Their solution interaction dynamics will be probed through liquid cell TEM. Thrust 2: Interactions forces between nanocrystals and organic mediators of mesocrystal formation – The interactions responsible for particle co-orientation and reorientation will be determined through a combination of dynamic force spectroscopy (DFS) and modeling. DFS will provide a direct measure of the free energy of the orientation dependent crystal-crystal and -polymer interactions. Experimental measurements are supported by molecular model-ing, which allows us to determine molecular details of the effective interactions and provides parameters for the phase field calculations in Thrust 3. Thrust 3: Post-nucleation particle ag-gregation and co-orientation – The kinetics of particle aggregation, crystallographic orienta-tions of the aggregating particles as a function of time, and structural evolution of mesocrys-talline aggregates will be investigated by liquid cell TEM and ex situ HRTEM. Emphasis will be placed on distinguishing between oriented attachment and orientation following random aggregation either through whole-particle rotation or atomic-scale ripening. These data will be compared to phase-field models of mesocrystal assembly that utilize the interaction energies determined in Thrust 2.