Nucleation kinetics of calcium phosphate nanoparticles in reverse micelle solution

The nucleation kinetics of calcium phosphate nanoparicles in the reverse micelle solution was investigated in the present experiment. The reaction system consisted of cetyltrimethylammonium bromide (CTAB), cyclohexane, n-pentanol and reactant solution. The amorphous nuclei were mainly composed of dicalcium phosphate (DCPA, monetite) rather than hydroxyapatite (HA) because of the kinetic favor of DCPA. Nucleation kinetic parameters – the nucleation free energy ΔGC, the critical nucleus radii and critical nucleation number – were calculated with the model based on classical nucleation theory and UV–vis absorption spectra. The nucleation rate equation of nanoparticles prepared in reverse micelles solution was developed. Comparisons with classical nucleation equation showed that nucleation rate in reverse micelle solution was lower than those conducted in aqueous solution. A rational reason for this result is as follows: reverse micelles might condense reaction solution thus increasing its concentration. An increase in ion strength makes reverse micelles invulnerable which might disfavor the effective coalescence and the nucleation process as well.