Biomineralizing organisms routinely assemble materials with sophisticated design and advanced functional properties, often using amorphous precursors to access compositional and structural states far from equilibrium. Organic macromolecules and inorganic additives such as magnesium ion are thought to play an important role in controlling phase transformations in these systems. However, it has proven extremely challenging to accurately describe pathways and determine mechanisms, even for extensively studied system such as amorphous calcium carbonate (ACC). I will discuss recent work in my laboratory in which we use liposomes and microfluidic droplets as nano-to-microscale reactors to study the impact of confinement, biomolecules, and inorganic additives on the kinetics of crystallization of ACC and its barium-substituted derivative (ACBC). In the course of this work, we discovered bulk syntheses leading to two other metastable, yet crystalline carbonates that we call balcite and gortotowskite. Balcite is isostructural with a high temperature modification of calcite and has exceptional hardness; its kinetics of formation hint on a complex, possibly non-classical mechanism. Gortatowskite on the other hand is a barium carbonate monohydrate that crystallizes in quasi-two-dimensional habit. These findings demonstrate that microfluidic devices are a powerful tool in the study of phase transformations of the rich chemistry of metastable carbonates.

Nucleation and growth of crystalline carbonates from amorphous precursors

255th National Meeting (2018)

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