Continuous Structural Evolution of Calcium Carbonate Particles:  A Unifying Model of Copolymer-Mediated Crystallization

Abstract

Two double-hydrophilic block copolymers, each comprising a nonionic block and an anionic block comprising pendent aromatic sulfonate groups, were used as additives to modify the crystallization of CaCO3. Marked morphological changes in the CaCO3 particles were observed depending on the reaction conditions used. A poly(ethylene oxide)-b-poly(sodium 4-styrenesulfonate) diblock copolymer was particularly versatile in effecting a morphological change in calcite particles, and a continuous structural transition in the product particles from polycrystalline to mesocrystal to single crystal was observed with variation in the calcium concentration. The existence of this structural sequence provides unique insight into the mechanism of polymer-mediated crystallization. We propose that it reflects continuity in the crystallization mechanism itself, spanning the limits from nonoriented aggregation of nanoparticles to classical ion-by-ion growth. The various pathways to polycrystalline, mesocrystal, and single-crystal particles, which had previously been considered to be distinct, therefore all form part of a unifying crystallization framework based on the aggregation of precursor subunits.

Calcite mesocrystals: a very effective block polyelectrolyte for crystal "Morphing"

“…A continuous transition in building unit particle size to molecules on the one hand and of decreasing mutual order of the nanoparticle subunits on the other, places mesocrystals as structural intermediate between a classical single crystal composed of atoms/ions/molecules and a polycrystal without any mutual order between its nanoparticle subunits. 6) This intermediate structure of mesocrystals between single crystal and polycrystal was very recently also found for Ag mesocrystals. 7) Mesocrystals are usually not stable against crystallographic fusion of their nanoparticle subunits to a single crystal, if their nanoparticle subunits are in crystallographic register, since the subunits are aligned and the system can win a substantial amount of energy by elimination of these internal surfaces.…”

Nacre, a Natural Biomaterial

“…It is conceivable that this organic ring structure acts to nucleate aragonite into the highly oriented nano-crystals (~50 nm in size) that make up the meso-crystal (i.e. µm sized) nacre tablets (Wohlrab et al, 2005;Kulak et al, 2007). This adds support for a highly dynamic biomineralization process during which organic materials and carbonate precursor phases (likely amorphous) are delivered to the site of nacre tablet formation from the overlying mantle with a high degree of spatial control.…”

Inorganic Self-Organized Silica Aragonite Biomorphic Composites

“…Wang et al 10 synthesized complex "flower type" vaterite superstructures in the presence of urea at high temperatures. Kulak et al 11 reported a variety of CaCO 3 particles of varying crystallinity in the presence of two double-hydrophilic block copolymers. Walsh et al 12 described a method for synthesizing hollow porous shells of crystalline aragonite that resemble the coccospheres of certain marine algae.…”