Polymorph Switching in the Calcium Carbonate System by Well-Defined Alginate Oligomers

• Published in: Crystal growth & design Vol. 11; no. 2; pp. 520 - 529
• Main Authors: Olderøy, Magnus Ø, Xie, Minli, Strand, Berit L, Draget, Kurt I, Sikorski, Pawel, Andreassen, Jens-Petter
• Format: Journal Article
• Language: English
• Published: Washington,DC American Chemical Society 02.02.2011
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Crystalline state (including molecular motions in solids); Crystallographic aspects of phase transformations; pressure effects; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Materials science; Methods of crystal growth; physics of crystal growth; Organic compounds; Physics; Solid-solid transitions; Specific phase transitions; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation; Crystal growth; pH value; Nucleation; Growth rate; Macromolecules; Crystallization; Crystal seeds; Calcite; Precipitates; Switching; Oligomers; Proteins; Aragonite; Precipitation; Composite materials; Calcium carbonate; Growth mechanism; Crystal morphology; Polymers; Vaterite; Polymorphism; Crystal structure
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/cg101337g

Functional biominerals formed in living organisms require high control of inorganic phase crystal polymorphs, morphology, size, and orientation. Such control is often governed by both soluble and insoluble functional molecules, where the soluble ones usually are highly negatively charged proteins and polymers. Here, the effect of alginate and well-defined alginate oligomers on calcium carbonate crystallization is explored, by seeded and unseeded experiments, to separate the effects of the additive on the crystal growth process from the effect on nucleation. The experiments were done at well-defined activity-based levels of supersaturation, controlled pH and temperature. In the seeded experiments, crystal growth of calcite, aragonite, and vaterite were studied separately, and the observations were used to explain a switch in polymorphism when alginate oligomers were present during the crystallization process. Unseeded experiments showed that low concentrations of G-blocks (oligomers of α-l-guluronic acid) switched the precipitation product from aragonite and vaterite to calcite, at conditions that would normally precipitate only aragonite or vaterite. This effect was explained by growth inhibition of aragonite and vaterite, as shown by seeded experiments in the presence of G-blocks. The growth rate of calcite was not affected to the same extent, apart from the stabilization of faces other than {104}, which are usually expressed in additive free systems. These observations may be used to design composite materials at ambient conditions, inspired by the strategies nature applies to control biomineral formation.