Control of calcium carbonate crystallization by using anionic polymethylsiloxanes as templates

Sulfonated (SO3H-PMS) and carboxylated (CO2H-PMS) polymethylsiloxanes were synthesized and their effects as anionic template modifier on the CaCO3 crystal morphologies were evaluated. In vitro crystallization assays of CaCO3 were performed at room temperature by using gas diffusion method at different concentration, pH and time. SEM images of CaCO3 showed well-defined short calcite piles (ca. 5 μm) and elongated calcite (ca. 20 μm) when SO3H-PMS was used. When CO2H-PMS was used, the morphology of CaCO3 crystals was single-truncated at pH 7–9 and aggregated-modified calcite at pH 10–11. However, at pH 12 the least stable donut-shaped vaterite crystals were formed. EDS and XRD confirmed the presence of Si from anionic PMS templates on the CaCO3 surfaces and its polymorphism, respectively. Results showed that the selective morphologies of CaCO3 reflect the electrostatic interaction of anionic groups of functionalized PMS with Ca2+ adsorbed on CaCO3 crystals. Rounded and truncated-modified fluorescent CaCO3 was also produced by the inclusion of functionalized PMS into the lattice of CaCO3 matrix. We demonstrated that the anionic PMS offer a good modifier for polymer-controlled crystallization and a convenient approach for understanding the biomineralization field.