Study of Structures and Crystallization Behavior of Amorphous Calcium Carbonate (ACC) and its Application in Bio-inspired Materials

Abstract

Amorphous mineral phases, e.g. amorphous calcium carbonate (ACC) that occurs ubiquitously in nature, play a pivotal role in biomineralization processes and as such, are a focal point of vast interdisciplinary research. Studies into biogenic ACCs indicate the existence of different short-range orders, which can be understood within the notion of amorphous polymorphism (polyamorphism). It is speculated that distinct short-range orders in biogenic ACCs are triggered by various ions and biomolecules. However, it was shown that additive-free ACCs obtained from metastable solutions with equilibrated pre-nucleation clusters (PNCs) can also exhibit different proto-crystalline structures. The first part of this thesis concern with the importance of the existence of equilibrated PNCs for the development of proto-structures in ACCs. This was accomplished by directprecipitation of ACC in alcoholic media. Second, the role of pH and temperature in the development of short-range orders of ACCs is further explored. The aim is to complete and thereby corroborate the notion of ACC polyamorphism with the proto-aragonite (pa)-ACC form, which has not been reported for ambient pressures until now. Last, polymer-stabilized liquid precursors of CaCO3 were employed to selectively mineralize nanocellulose films via controlling the mineralization sites on nanocellulose fibres. The controlled mineralization enabled formation of mineralized and unmineralized layers of nanocellulose. This, in turn, yielded a bio-inspired, layered, nacre-like material outperforming the biological example in terms of plasticity.