Materials World Network: Particle-Mediated Control Over Crystallization: From the Pre-Nucleation Stage to the Final Crystal

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TECHNICAL SUMMARY:The formation of hierarchically organized crystalline solids through nanoparticle interaction and attachment is now recognized as a widespread phenomenon in environmental, biological and synthetic crystallization systems. The goal of this project is to develop a mechanistic understanding of how these so-called mesocrystals are created through particle-mediated growth processes. To achieve that goal, expertise in growth of mesocrystals will be combined with capabilities in high-resolution in situ transmission electron microscopy (TEM) and atomic force microscopy (AFM) imaging, dynamic force spectroscopy (DFS) of nanoparticle interactions, determination of atomic structure, and modeling and simulation from the atomic to mesoscale. Using calcium carbonate, iron oxide and calcium-silicate hydrate (SCH) combined with polymers as the experimental systems, the project will pursue three thrusts, structured around the key scientific issues. The nature of pre-nucleation clusters will be determined using ion potential measurements, titration and ultracentrifugation and their solution interaction dynamics will be probed through liquid cell TEM. The interactions responsible for particle co-orientation and reorientation will be determined through a combination of DFS and modeling. Experimental measurements will be supported by molecular modeling simulations, which will be used to determine molecular details of the effective interactions and provide parameters for phase field calculations. The kinetics of particle aggregation, crystallographic orientations of the aggregating particles, and structural evolution of mesocrystalline 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 assembly that utilize the experimentally determined interaction energies. The outcome will be a set of principles to guide synthetic strategies for creating hierarchically organized materials such as bioceramics, photonic solids, energy harvesting materials.NON-TECHNICAL SUMMARY:Through support from the NSF Division of Materials Research, a Materials World Network will be formed to investigate mechanisms by which complex crystalline structures, known as mesocrystals, are created through the interaction and attachment of nanoparticles. The goal of this research is to establish a mechanistic understanding of this process and a set of principles to guide synthetic strategies for creating hierarchically organized materials such as bioceramics, photonic solids, and energy harvesting materials. The work will be carried out by combining computer simulations and chemical analyses with a powerful set of in situ microscopy tools that provide real-time molecular-scale information about both nanoparticle attachment processes and the interaction forces between the particles. The materials to be investigated include those of relevance to biomaterials research, such as calcium carbonate, as well as those of relevance in energy and environmental systems such as iron oxide. The outcome will be a set of physical principles that can be applied both to understanding the processes responsible for formation of natural materials in the environment and to synthesis of hierarchical materials for energy, biomedical, and structural applications. Success of the project is enabled by an international collaboration between four US and German Universities, each of which brings a unique set of skills and knowledge to the project. Moreover, this collaboration will provide a unique learning experience for the graduate and undergraduate students involved in the research through international exchanges between the US and German labs. Finally, the project will include development of a module on mesocrystal formation for the public outreach programs to be made available through the NSF-funded Nanoscale Informal Science Education network.