Study of polymeric additive effect on calcium oxalate dihydrate crystal growth using real-time atomic force microscopy

Microscopic events associated with crystal growth and characterization of the growth hillocks on the (1 0 0) and (1 0 1) faces of COD were examined by atomic force microscopy. The (1 0 0) and (1 0 1) faces of COD developed elliptical and triangular hillocks and pits, respectively. Each face exhibited hillocks with step sites that can be assigned to specific crystal planes, enabling direct determination of the growth rates along specific crystallographic directions. The addition of macromolecules with anionic side chains, poly-l-aspartate, poly-l-glutamate, and polyacrylate resulted in inhibition of growth on the hillock step planes. The magnitude of their effect depended on the macromolecule structures and identity of the step site. The isotropic shape of the COD hillocks mimicked the shape of the resulting macroscopic COD crystals based on step-specific binding of the macromolecules to the COD crystal, with stronger step pinning along the [0 1 0] direction than in the [0 0 1] direction. Electrostatic matching between the crystal faces and additives according to the ionic array of calcium oxalate in the COD structure was found to be responsible for the preferential binding of the macromolecules to terraces.

► Influence of biopolymers on growth of (1 0 0) and (1 0 1) faces of COD is measured by real-time AFM.
► Magnitude of influence of biopolymers depends on biopolymer structures and identity of step site of crystal faces.
► PolyAA exhibits the strongest inhibition effect on growth of both crystal faces.