Dichroic calcite reveals the pathway from additive binding to occlusion

David C. Green, Robert Darkins, Bartosz Marzec, Mark A. Holden, Ian J. Ford, Stanley W. Botchway, Bart Kahr, Dorothy M. Duffy, Fiona C. Meldrum

Research output: Contribution to journalArticlepeer-review


Organic additives play key roles in controlling the precipitation of calcium carbonate in the environment, industry, and biology, where they can direct polymorphism, alter crystal morphologies, and sometimes even become occluded, modifying bulk properties. However, significant questions remain regarding the pathway from adsorption on crystal surfaces to occlusion. Here, the optical properties of calcite crystals grown in the presence of the dye Congo red are used to characterize the organization of the additives within the crystal. Complemented by the analysis of surface adsorption through in situ atomic force microscopy (AFM), molecular simulations, and changes in crystal morphologies, we show that the occluded dye molecules are randomly oriented under fast growth conditions, but that slow growth engenders ordering of the dye within islands, whose orientation is determined by the dye/terrace interaction free energy. The islands are subsequently overgrown such that their internal structure is preserved. These results reveal that the occlusion of organic macromolecules into calcite can be understood by thermodynamics operating at the adsorption stage. This new insight will ultimately enable the design of additives to give specific material properties.

Original languageEnglish (US)
Pages (from-to)3746-3755
Number of pages10
JournalCrystal Growth and Design
Issue number7
StatePublished - Jul 7 2021

ASJC Scopus subject areas

  • General Chemistry
  • General Materials Science
  • Condensed Matter Physics


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