Control of the precipitation through polymeric additives and/or seeding
The use of polymeric additives is an efficient way for controlling precipitation. By changing the charge at the surface of the particles, or by adsorbing onto specific crystal planes, modification at the crystal growth or morphology can be induced.
The organic additive HPMC showed an important change in copper oxalate morphology and the primary particle growth. The polymer seems to adsorb preferentially on the surface of primary particle that have a hydrophobic character, leading to an asymmetric growth. For these particles a simple mechanism of nucleation, growth by molecular attachment, and then growth by an ordered aggregation “brick-by-brick” was proposed.
Morphology of copper oxalate with different concentration of HPMC 100 (Publication)
Further work showed a more complex mechanism (Publication).
The precipitation of calcium carbonate can be controlled by the conjugated action of the polymeric additive polyacrylic acid (PAA) and seeding by. “Nanoseed suspensions” were prepared from a seed source (commercial powder of calcite of high specific surface area), suspended in the potassium carbonate reactant containing PAA. They were treated in an ultrasonic bath, and filtered through a 0.2 μm membrane. The reaction between this suspension and a solution of calcium nitrate leads to different morphologies, depending on the seed source, and the PAA concentration.
Morphology of calcium carbonate with different concentration of PAA using a seed source (Publication)
PAA has also been shown to significantly influence other systems, such as cerium oxide.
Morphology of ceria precipitated with different concentrations of PAA
Morphology of cobalt oxalate dihydrate was greatly influenced by the concentration of PMMA.
The interaction of organic molecules with the surfaces of inorganic particles can be approached through atomistic simulations. Such a study has been conducted on hematite growth, considering the effect of two phosphonate additives (methyl nitrilo-dimethylenephosphonic acid – MNDP, and ethylenediamine tetraphosphonic acid – EDTP).The morphologies predicted by the calculations are in good agreement with the TEM pictures obtained experimentally, validating the use of this technique as a predictive tool for the synthesis of tailor-shaped nanocrystals. Links/Publications: