Biomimetic synthesis of calcium carbonate thin films using hydroxylated poly(methyl methacrylate) (PMMA) template

Morphosynthesis of calcium-rich materials by tuning the chemical structure of organic matrices has tremendous potential in the preparation of functional mineralized materials. In this paper, we have demonstrated the deposition of thin films of CaCO3 by subtle modifications of the backbone of poly(methyl methacrylate) (PMMA) by the incorporation of many hydroxyl groups. The water-insoluble hydroxylated PMMA (HyPMMA) was used as a template along with poly(acrylic acid) (PA) as an additive for CaCO3 mineralization. Thin film deposition was controlled by the addition of an appropriate amount of PA to the crystallization medium. At lower concentrations (PA = 50 and 100 mu g/mL), irregular aggregates of calcite crystallites were formed. As the concentration of PA was increased (500 mu g/mL and 1 mg/mL), calcite thin films were deposited. Time-dependent crystallization showed that the precipitates obtained after 3 h were biphasic in structure, consisting of both amorphous and crystalline domains. Observations suggest that crystal aggregates and thin films were formed through a multistep mechanism in which an amorphous phase was deposited initially and was subsequently transformed into stable crystalline form. In contrast, mineralization in the presence of HyPMMA or PA alone yielded only calcite or calcite aggregates. Our results indicate that a concerted interplay of interactions between the insoluble polymer matrix (HyPMMA) and soluble PA determines the growth and morphology of CaCO3 by influencing the transformation of amorphous calcium carbonate (ACC) into the crystalline phase. More specifically, we have investigated the interplay of the role of acid groups on PA and accelerating alcohol groups on HyPMMA in calcium carbonate crystallization.