Synthesis and Structure-Property Relationships of Single Crystal Nanocomposites

The work in this thesis explores the ability of cationic additives to direct the crystallization of calcium carbonate. Although considered less potent than their acidic counterparts, cationic additives are shown to enable exceptional control over the size, morphology, composition, structure and polymorph of the mineral. In particular, functionalization of polymer and metal nanoparticles with polycations enables their incorporation at exceptional levels within calcite (CaCO3) and alternative carbonate, sulfate and oxide single crystals. These nanocomposites are endowed with new optical properties including bright fluorescence and surface-enhanced Raman scattering. Computation simulations provide crucial insights into the molecular interactions between these cationic additives and host crystals, and structural analyses using synchrotron powder XRD reveal high lattice strains. The internal structures of the nanocomposites can also be controlled by annealing, providing a straightforward strategy for engineering the thermal and optical properties. Cationic polyamines can additionally direct the formation of all three anhydrous polymorphs of calcium carbonate, where aragonite (metastable phase of CaCO3) was observed to form via a particle attachment mechanism reminiscent of the growth of biogenic aragonite. Alternative hybrid single crystals are also explored, where protein nanogels impregnated with diverse (bio)-active compounds are incorporated within calcite. The host crystal effectively protects the payloads, and controlled release can be achieved by dissolution of the mineral in acidic solutions. Finally, while most bio-inspired strategies used to synthesize nanocomposites are carried out in pure aqueous solutions, the introduction of small amounts of organic co-solvents in the crystallization medium is shown to significantly enhance incorporation of various additives within inorganic crystals. This constitutes a significant step-change in methodology, which can find applications in a wide range of industrial fields. This work therefore delivers new insights into the structure-composition-property relationships of composite crystals and offers new straightforward synthetic routes for generating nanocomposites with advanced functional properties.