On the Bimodal Effects of Silicic Acids on Calcite Growth
Crystal Growth & Design 9(9): 4084-4090
The effects of silicic acids on calcite growth area model for the effects of partially polymerized additives on crystal growth. At alkaline pH, silicic acid polymers coexist with small mono- and oligomers, Atomic force microscopy (AFM) showed that large polymers promote two-dimensional nucleation, while mono- and oligomers have a bimodal promoter/inhibitor effect on step propagation. This bimodality can be interpreted as the result of attachment of mono- and oligomers along the steps along with a modification of the kinetics of kink generation and/or propagation. The bimodal step kinematic effect is accompanied by a single morphologic effect: growth islands transform from a rhombus into an ellipse. This effect has been reported for other additives, indicating that many additives generate few morphologies. Such a convergence limits the versatility of chemical control on biomorphogenesis. Contrarily, the strong kinetic effect of silicic acids may make them very efficient controllers of biomorphogenesis, if coupled with a physical shape control, for example, by templates. Thus, silicic acids show a unique bimodality as a controller of calcite biomineralisation and its an abundant biomineral.