Mechanistic Approach to Predict the Combined Effects of Additives and Surface Templates on Calcium Carbonate Mineralization

The biomineralization of calcium carbonate is masterfully directed by organic macromolecules present in many organisms. In this biomimetic study, absorbance measurements accompanied by microscopy and infrared spectroscopy are used to evaluate the superposed effect of organic additives and surface chemistries on the kinetics of surface-directed nucleation and growth of calcium carbonate. Polyelectrolyte films with carboxylic and/or amine groups serve as the organic template for mineralization, and amino acids and monosaccharides as the selected solution additives. A grain-boundary kinetics model describes surface precipitation of calcium carbonate to provide a mechanistic insight into the precipitation pathway via two parameters, the near-surface supersaturation and the crystal number density. While an organic matrix rich in ternary amines strongly promotes vaterite nucleation, the selected carboxylic-enriched polyelectrolyte film significantly stabilizes ACC in the near-surface region, while it equally promotes vaterite and calcite nucleation. The combined effect of organic additive and surface template determines the near-surface supersaturation. Soluble additives can also be directly involved in surface nucleation if they strongly interact with the organic interface. Our mechanistic approach reveals two different precipitation pathways that result from the synergy between surface template and organic additives.