Crystallization and Transformation mechanism of Calcium Carbonate Polymorphs and the Effect of PEG-PPG block copolymers

Abstract

The fast mixing of aqueous solutions of calcium chloride and sodium carbonate could immediately result in amorphous calcium carbonate(ACC). Under vigorous stirring, the formen ACC in the precipitation system will dissolve first and, then, transform within minutes to produce crystalline forms of vaterite, aragonite and calcite. After that, the solution-mediated mechanism dominates the transformation of the thermodynamically unstable vaterite into the thermodynamically stable calcite. Although ACC is the least stable form of the six anhydrous phases of calcium carbonate (CaCO₃),it could be, however,produced and stabilized by a variety of organisms. To better understand the formation-transformation mechanism of crystal structure of various calcium carbonates (CaCO₃), ex-situ methods(i.e.,SEM, FT-IR, XRD) were used to characterize the formation-transformation process of ACC and vaterite in aqueous systems with block copolymers, showing that ACC sampled at different conditions has different properties (i.e.morphology,and spectrum characterization). It is also very interesting to capture the obviously polycrystalline particles of CaCO₃during the transformation process through the effect of tir- or di-block copolymers which are tri block copolymers as poly(ethylene oxide)-block- poly(propylene oxide)-block-poly-(ethylene oxide) EO13PO30EO13 (Pluronic L64) and di-block copolymer as poly(ethylene glycol-co-propylene glycol) (PEGPG).