Influence of the Type of Surfactant on the Formation of Calcium Phosphate in Organized Molecular Systems

Organized molecular systems (OMS) have been widely used in the formation of mineral solids to control their composition, morphology, and dimensions. In this paper, we synthesized tricalcium phosphate by mixing two microemulsions, one containing calcium in its aqueous phase, the other containing phosphate. The microemulsions were stabilized either with the nonionic surfactant, Brij 30, or with the ionic surfactant, AOT, in n-decane. In the presence of Brij 30, the amorphous tricalcium phosphate gel formed was composed of spherical clusters and its crystallization into apatite used a process comparable to that observed in aqueous or water−alcohol medium. In contrast, the presence of AOT induced the production of a directly crystallized solid containing organic material, which could be due to AOT molecule preorganization at the oil−water interface. The growth of crystallites occurred in a preferential direction, and the crystals obtained were analogous in shape and size to particles of bone mineral. We develop the hypothesis of oriented apatitic nucleation on the organized AOT molecule support.