Interfacial control of nucleation of calcium carbonate under organized stearic acid monolayers

Abstract

The nucleation and crystal growth of calcium carbonate from supersaturated bicarbonate solutions in the presence of stearic acid monolayers has been studied by electron microscopy and electron and X-ray diffraction. Whereas rhombohedral crystals of calcite are randomly deposited in the absence of the monolayer, regiospecific crystallization of vaterite florets occurs at the organic surface. The florets develop initially as single crystalline biconvex discs oriented with respect to the negatively charged headgroups of the organic membrane such that the radial axis, which corresponds to the crystallographic [0001] direction, is aligned perpendicular to the monolayer interface. Subsequent radial outgrowth results in the polycrystalline floret morphology. The degree of compression of the monolayer results in significant changes in nucleation. Solid-phase films are highly catalytic and generate vaterite discs with a wide size distribution. In contrast, nucleation on liquid-phase monolayers results in discs of more uniform particle diameter. Increased supersaturation and uncompressed films gave both calcite and vaterite polymorphs. Preferential orientation of the ab vaterite crystal face parallel to the monolayer surface is discussed in terms of the electrostatic accumulation of a Stern layer of Ca ions. Polymorph selectivity is determined by kinetic factors involving charge accumulation and possibly stereochemical recognition between the alignment of the stearic acid carboxylates and the orientation of carbonate anions in the vaterite unit cell. Geometric (epitaxial) matching at the interface is not a primary factor in regulating nucleation.

Precipitation of different calcite crystal morphologies in the presence of sodium stearate

“…As a result, a hydrophobic alkyl chains is chemisorbed to the mineral surface, thus affecting the surface forces between the filler and the polymer matrix. On the other hand, the knowledge on the minimum quantity of fatty acid molecules that could produce the hydrophobic precipitate suitable for use as filler in polymer materials is of importance, because the precipitation could affect crystal nucleation and/or crystal growth of CaCO 3 [16][17][18][19][20][21].…”

Effect of Langmuir monolayer of bovine serum albumin protein on the morphology of calcium carbonate

“…Langmuir monolayer is an excellent candidate for this purpose: they are already in contact with water, they are ordered, and their structures are well-known and can be varied by changing pressure, temperature and other experimental parameters. Recently, the nucleation of inorganic crystals under Langmuir monolayer has been extensively studied [13][14][15][16][17][18]. Mann and coworkers have performed extensive studies of the nucleation of calcium carbonate [13,14], barium sulfate [15].…”

“…Recently, the nucleation of inorganic crystals under Langmuir monolayer has been extensively studied [13][14][15][16][17][18]. Mann and coworkers have performed extensive studies of the nucleation of calcium carbonate [13,14], barium sulfate [15]. They found that preferentially nucleated crystals would be prepared under organic Langmuir monolayer with specific polymorphs and specific lattice orientations.…”

Oriented Crystallization of KH2PO4 under a Compressed Langmuir Monolayer

“…A new field, usually named biomineralization, has received considerable attention and has been developed very rapidly in recent years. − A development in this area involves the use of Langmuir monolayers of surfactant molecules as molecular templates for the oriented nucleation of organic and inorganic crystals. Because of ion binding, lattice matching, and structural and stereochemical complementarity between the monolayer and the crystal, very high selectivity in the nucleation and growth of crystal can be observed. − The ability to control the crystallization of inorganic solids is critical to improve technological use of materials currently and in the future …”