Nonclassical Crystallization:  Mesocrystals and Morphology Change of CaCO₃ Crystals in the Presence of a Polyelectrolyte Additive

Abstract

Crystallization of calcite from differently concentrated calcium chloride solutions by the CO2 gas diffusion technique in the presence of polystyrene sulfonate yields crystal superstructures with unusual morphology. From the typical calcite rhombohedra as a starting situation, the morphology can be systematically varied via rounded edges and truncated triangles to finally concavely bended lens-like superstructures. Although these "crystals" are apparently well-faceted in light microscopy, electron microscopy analysis and BET reveal that the structures are highly porous and are composed of almost perfectly 3D-aligned calcite nanocrystals scaffolded to the final, partly nicely curved superstructures. At high supersaturations, superstructures with changed symmetry indicative of dipolar interaction potentials between the building blocks are found. The present model case also gives evidence for the importance of nonclassical, mesoscopic processes in crystallization in general.

The Effect of Additives on the Early Stages of Growth of Calcite Single Crystals

“…The size at which an additive begins to affect the morphology of calcite depends on the additive binding strength, the concentration, and the supersaturation, which was rationalized by considering additive binding to available kink sites. Our data also confirm that calcite grows by a classical ion‐by‐ion mechanism in the presence of PSS18 rather than a non‐classical assembly of nanoparticles 27. These results provide insight into the growth mechanisms of sparingly soluble crystals such as calcite, and show that it is important to consider the action of additives on nucleation and growth to obtain product crystals with the desired properties.…”

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

“…The mineralisation was performed by a slow CO2 gas diffusion technique as described in our previous papers. 43), 44) To investigate the effect of added polymer, crystallizations were performed in the presence of different concentrations of polymer and CaCl2 in glass bottles with glass slides, which were put into the same closed desiccator at room temperature. All glassware including glass bottles and small pieces of glass substrates were cleaned as follows: firstly sonicated in ethanol, then rinsed with distilled water, further soaked with a H2O-HNO3 (65%)-H2O2 (1:1:1, v/v/v) solution, then rinsed with doubly distilled H2O, and finally dried at room temperature.…”

“…42) Despite the rapidly increasing number of observations of mesocrystals, relatively little is yet known about their formation mechanism. In a series of papers 43)- 45) we demonstrated that addition of a simple polyelectrolyte as poly (styrene sulfonate) can modify the crystal growth of calcium carbonate in a manifold fashion leading to nanocrystal superstructures with astonishing complexity. The remarkable change from the typical single crystal calcite rhombohedron with (104) faces to mesocrystals presenting their unusual {001} faces with additional rounded edges was outlined.…”

“…48) In addition, the bound polymers can induce a directed aggregation through a change of interaction potentials, which can be highly directional and anisotropic. 43), 44) Usually, the added polymers have one or more than one, if not all roles of that list.…”

Nonclassical Crystallization of Dipicolinic Acid in Microemulsions

“…Nevertheless, mesocrystal formation has been reported for a wide range of materials, including biominerals 16,17 (e.g. sea urchins 18 and hydroxyapatite 19,20 ) and metal complexes (e.g.…”