The Influence of Additives and Impurities on Crystallization Kinetics

Expressions describing the influence of additives and impurities on the kinetics of mineralization and demineralization have been derived from an interfacial tension point of view. In aqueous solution, the Lifshitz-van der Waals interfacial tension component changes very little, but the Lewis base (or electron-donicity) surface tension parameter varies markedly as a function of additive and impurity concentrations. The inhibiting effects of simple cations on crystal growth in solution may result from the increase in interfacial tension accompanying their adsorption on the surfaces. In the case of polymers or macromolecules, the kinetics of crystallization will not only depend upon the substrata but also the surface properties of the additives. Nucleation of calcium phosphate phases was observed only on surfaces having low solid/solution interfacial tension and relatively high electron-donicity of the solid surfaces. Such properties were found for human serum albumin immobilized on polymer solid surfaces of poly(methyl methacrylate) (PMMA) and poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP), and following radiofrequency glow discharge (RFGD) treatment which mimicked the adsorption of impurity OH− ions on the surfaces.