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Nano- and Mesoscale Structures of Amorphous Calcium Carbonate Indicate Nanoscale Assembly Processes
preprintsubmitted on 24.03.2021, 14:54 and posted on 26.03.2021, 13:43 by Simon M. Clark, Bruno Colas, Dorrit E. Jacob, Jӧrg Neuefeind, Hsiu-Wen Wang, Katherine L. Page, Alan K. Soper, Philipp I. Schodder, Patrick Duchstein, Benjamin Apeleo Zubiri, Tadahiro Yokosawa, Vitaliy Pipich, Dirk Zahn, Erdmann Spiecker, Stephan E. Wolf
Here, we approach the issue of ACC ultrastructure by applying a method for determining atomically resolved structures of amorphous materials using Monte Carlo simulations constrained by both X-ray and neutron scattering data. This structural analysis approach allows us to develop a detailed model for ACC at the atomic level. Our findings reveal that synthetic ACC, rapidly precipitated at high pH, consists of two-nanometer sized units containing a high degree of near range order similar to partially disordered nano-crystals. Small-angle scattering analyses show a multi-scale hierarchical organisation of the structure, supportive of a multi-step colloid self-assembly process. Computer simulations and high-resolution transmission electron microscopy show that the mesostructure of ACC resembles that of a glassy gel with crystalline material in domains. Our findings support the formation of ACC by a nanoparticle aggregation process that likely starts from prenucleation clusters in solution.