| As a chemical-based materials synthesis technique, the reverse microemulsion methods preparing nanosized particles have been developed in recent decades. In the microemulsions-mediated methods, the nanosize water droplets show thermodynamically stabilization by the means of the surfactants (sometimes and cosurfactants) films, that serve as nanosize test tubes, thus limiting particles growth and minimizing particle aggregation. The technique have been applied in some fields including inorganic nanoparticles synthesis, organic polymerization and enzyme catalyst activitization.Hydroxyapatite (also called as HAP below) as the basic mineral component in man and animal bone play an important role in clinical medicine. For artificial hydroxyapatite, the properties of products are strongly effected by the size, the morphology and the surface of particles. The microemulsion-mediated synthesis of hydroxyapatite offers the unique ability to control particles size, morphology and surface properties.AOT/isooctane/water microemulsions admit to form spherical water cores, which in diameter depends linearly on the water content w ( water-surfactant molar ratio). The best compositions and contents of AOT reverse microemulsion in the work were studied by measuring the maximum amount of solubilizing water in micelles from the abrupt change of electroconductivity. The reactants for producing HAP particles were monocalcium phosphate monohydrate (Ca(H2P04)2 ?H2O, called as MCPM below) and calcium hydroxide saturate solution. The two microemulsions containing above two reactants were characterized by a series of analysis methods including dynamic light scattering(DLS), infrared spectrometer(IR), ultra-visible spectrometer(UV), nuclear magnetic resonance (NMR), electroconductivity measure. In the partial ternary phase diagram of AOT/isooctane/MCPM or Ca(OH)2 solution, the single phase areas of microemulsions become compressed because of the effect ofreactants as electrolytes. The diameter of water cores measured by DLS were also slightly reduced, but still depended on the water content w. With the increase of water content, the influence of reactant concentration on the diameter of water cores became stronger. As the solubilization of water and reactant ions within the water cores, water molecular were bounded in the near of polar head group of AOT (as bound water) by hydration interaction and hydrogen bridges at low water content (w=8.3). While higher water content(w=16.6), an amount of water in the inner water cores were in the center of water cores (as free water). Ca2+ ions from the reactants attended to be absorbed in the diffusion dilayer by the SO3- anion. Calcium ions could compress the diffusion dilayer and reduce the aggregation number of AOT molecular because of the higher charge density. The absorbance of Ca2+ ions change of phasediagram of system and water core diameter. Both of the increase in water content w?and reactant concentration made the effects stronger.Two microemulsions containing reactants being mixed, HAP particles began to form. HAP particles were characterized by dynamic light scattering, auger energy spectrum, XRD, IR spectrum and TEM. The size of HAP particles derived from AOT microemulsion is about 5~10 nm, which grow to above 10 nm when particles were separated from microemulsion solution. Particles was coated by AOT and octanol molecular in about 2 nm depth. HAP particles were poor crystalline and transformed into the better crystal after calcinated at 650Cfor 4 hours. In morphology, little spherical particles with the diameter of about 10 nm aggregated into 70~100nm particles that could easily be dispersed in water. Particles were still in spherical morphology after calcinated.The process of particle formation is mechanically limited by the collision, fusion and exchange between water droplets. Furthermore, the key microemulsion properties of interest are the size of the water cores, the average number of water cores, the average occupancy number of reactant ions per water cor...
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