Insight into shape control mechanism of calcium phosphate nanoparticles in reverse micelles solution

The present experiment demonstrates a systematic morphosynthesis of calcium phosphate crystals with controlled morphology in reverse micelles solution of CTAB/n-pentanol/ water /cyclohexane. Well-defined morphologies of calcium phosphate particles, such as nanowires, tablets, brushlike particles, and fiber bundles, can be prepared. The microstructural characteristics of the CTAB/n -pentanol/water/cyclohexane reverse micelles solution has been investigated by FTIR spectroscopic, P-31 NMR, and UV-visible absorption spectra techniques, demonstrating that the molar ratio of water to surfactant (W-o) and n-pentanol to surfactant (P-o) showed significant effects on the morphology of the resulting particles. At lower W-o and P-o, CTAB played a role in guiding the growth direction. With increasing W-o and P-o, crystal growth lost the direction-guiding capability of CTAB. However, as crystal growth modifiers, water and cosurfactants follow different mechanisms. The solubility of water causes a decrease in bound water layer, resulting in a decrease in interactions between CTA(+) and PO43- which invalidates the shape control of surfactant molecules. The loading of cosurfactant (n-pentanol) results in decreasing the rigidity of the reverse micelles interface. This in turn favors the shape fluctuations of reverse micelles, inducing crystal development.