(170g) Influence of Polymeric Additives On the Nucleation Kinetics, Growth, and Polymorph Selectivity of Calcium Salts

We investigate the factors that control the nucleation and growth of important calcium biominerals such as calcium carbonate, calcium oxalate, and calcium phosphate. We establish that macromolecules (polyelectrolytes, polypeptides, surfactants) can control the final morphology and polymorph by i) face-selective adsorption on crystals (thermodynamic regime) or by ii) temporarily stabilizing the primary nanoparticles formed thus leading to mesoscale crystallization (kinetic regime). A combination of techniques which include Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), and Calcium Ion Selective Electrode have been used to evaluate the effect of macromolecules on the nucleation, growth, and the morphology of obtained crystals.  For example, sodium polystyrene sulfonate (PSS) was found to affect the morphology of the produced crystals and to preferentially promote the crystallization of calcium oxalate dihydrate (COD) over the thermodynamically stable calcium oxalate monohydrate (COM). At sufficiently high PSS concentrations, all calcium ions participate in complex formation with PSS and thus, the crystallization of calcium oxalate was completely inhibited. The effects of PSS on the nucleation and growth of calcium oxalate were remarkably reduced or completely eliminated when a cationic surfactant molecule was introduced in the system.