Crystallization of calcium carbonate mineral with hierarchical structures in DMF solution under control of poly(ethylene glycol)-b-poly(L-glutamic acid):: Effects of crystallization temperature and polymer concentration

CaCO3 superstructures with complex forms and hierarchical surface textures were mineralized in the presence of peptide type block copolymer poly(ethylene glycol)-b-poly(L-glutamic acid) (PEG-b-pGlu) as a crystal growth modifier in dimethyl formamide (DMF) solution. Spindle-like CaCO3 crystals with a rather smooth surface and a size of 10 mu m in length and a maximum diameter of 6 mu m were mineralized at 24 +/- 2 degrees C. Unique ellipsoid-like CaCO3 particles with many similar thorns distributed on the particle surface formed when the mineralization temperature was kept at 14 +/- 2 degrees C. Complex column-like CaCO3 superstructures comprised of many tiny rods and irregular particles were observed at 4 +/- 2 degrees C. In addition, when the reagent concentration is varied, the morphology of CaCO3 changes from a mixture of spherical and ellipsoidal structures to a kind of complex ellipsoidal superstructure whose surface is attached by many hierarchical tubular structures, and then to a complex columnar structure, when the concentration of Ca2+ ions was varied from 40 to 20 mM and finally decreased to 10 mM, respectively. Correspondingly, phase transition occurred from a mixture of aragonite and calcite to pure calcite, and then to a mixture of vaterite and calcite when the mineralization temperature increased. Moreover, changing the polymer concentration resulted in phase transition from calcite to a mixture of aragonite and calcite, and then to a mixture of vaterite and calcite. An emergent self-organization process and its combination with an aggregated mechanism have been proposed for the formation of the complex ellipsoidal superstructures. The results imply that the specific biomimetic synthesis strategy in a nonaqueous solution can provide a useful pathway to produce inorganic or inorganic/organic hybrid materials with a unique morphology and specific textures.