Premium
Amorphous Calcium Carbonate is Stabilized in Confinement
Author(s) -
Stephens Christopher J.,
Ladden Sophie F.,
Meldrum Fiona C.,
Christenson Hugo K.
Publication year - 2010
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201000248
Subject(s) - materials science , crystallization , crystallinity , calcite , amorphous solid , calcium carbonate , monolayer , chemical engineering , surface energy , amorphous calcium carbonate , chemical physics , nanotechnology , crystallography , mineralogy , composite material , chemistry , engineering
Biominerals typically form within localized volumes, affording organisms great control over the mineralization process. The influence of such confinement on crystallization is studied here by precipitating CaCO 3 within the confines of an annular wedge, formed around the contact point of two crossed half‐cylinders. The cylinders are functionalized with self‐assembled monolayers of mercaptohexadecanoic acid on gold. This configuration enables a systematic study of the effects of confinement since the surface separation increases continuously from zero at the contact point to macroscopic (mm) separations. While oriented rhombohedral calcite crystals form at large (>10 µm) separations, particles with irregular morphologies and partial crystallinity are observed as the surface separation approaches the dimensions of the unconfined crystals (5–10 µm). Further increase in the confinement has a significant effect on the crystallization process with flattened amorphous CaCO 3 (ACC) particles being formed at micrometer separations. These ACC particles show remarkable stability when maintained within the wedge but rapidly crystallize on separation of the cylinders. A comparison of bulk and surface free‐energy terms shows that ACC cannot be thermodynamically stable at these large separations, and the stability is attributed to kinetic factors. This study therefore shows that the environment in which minerals form can have a significant effect on their stability and demonstrates that ACC can be stabilized with respect to the crystalline polymorphs of CaCO 3 by confinement alone. That ACC was stabilized at such large (micrometer) separations is striking, and demonstrates the versatility of this strategy, and its potential value in biological systems.