Preparation and characterization of nanosized hydroxyapatite particles in AOT inverse microemulsion

Nanosized particles of hydroxyapatite (HAP) were synthesized by reacting Ca(H₂PO₄)₂·H₂O solution complex with equimolar Ca(OH)₂ saturated solution in sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/isooctane water-in-oil microemulsion. The formation of microemulsion strongly depended on water content w (w = [H₂O]/[AOT] molar ratio) and concentration of surfactant and cosurfactant (1-octanol). By the variety of conductivity with w and the partial ternary phase diagram derived from a series of demarcation points, we set the basic component of microemulsions: [AOT] = 0.1 M(mol/dm³), [1-octanol] = 0.1 M and w = 3-9. Dynamic light scattering (DLS), UV-visible absorbance, TEM analysis and X-ray diffraction were used to characterize the microemulsion, formation of particles and resulting HAP particles. At low water content (w < 9), the water pool radius of the droplet in the Ca(H₂PO₄)₂·H₂O microemulsion lineally depended on w. The size of final HAP particles was strongly affected by water content w and reactant concentration. With increasing water content w from 3 to 9, the size of HAP particles increased from 10-20 nm to 40-50 nm at reactant concentration [Ca(H₂PO₄)₂·H₂O] = 12 × 10 ^-3 mol/dm³. The resulting HAP particles were poorly crystallized and spherical in morphology.