Influence of poly(acrylic acid) on apatite formation studied by in situ X-ray diffraction using an X-ray scattering reaction cell with high-precision temperature control

Organic additives influence crystallization processes in a multitude of ways. In biomineralization, e.g. bone or shell, such additives play a crucial role in morphology, and in polymorph and size control. However, the specific interactions between the additives and the growing mineral are in general unknown. Here, a model of bone mineralization, namely the formation of apatite nanocrystals under the influence of poly(acrylic acid), is studied using in situ X-ray diffraction. Since the kinetics of these reactions are very temperature dependent, a new X-ray scattering reaction cell has been developed that allows very high temperature precision, with an r.m.s. variation during operation of similar to 0.05 K. The performance of the cell and its use in studying the apatite/poly(acrylic acid) system are discussed. The apatite formation process proceeds via the formation of an amorphous precursor which then crystallizes. It is found that poly(acrylic acid) retards crystallization and reduces the growth rate of the forming crystallites.