Electrical Conductivity Of Reverse Microemulsion In The Preparation Of Alumina Nanoparticles

Spherical alumina nanoparticles with homogeneous size distribution and good dispersity are obtained successfully by double-microemulsion.Water nucleus in the four-component system of Cetyltrimethyl Ammonium Bromide (CTAB) /n-butanol/cyclohexane/ aluminum nitrate (ammonia liquor) microemulsion is used as form board, where aluminum nitrate and ammonia liquor react.This article contains two parts: the choice of reverse microemulsion and the preparation of alumina nanoparticles.The four-component system of CTAB/n-butanol/cyclohexane/water microemulsion is studied by measuring the electrical conductivity and watching. Some factors are changed, such as the content of surfactant CTAB, cosurfactant n-butanol and the type of disperse phase. The effect of these factors on the maximum volume of solubilizing water and stability of the water-in-oil system is discussed. The reverse microemulsion with proper proportion is found by experiment, and then alumina nanoparticles with different particle size are prepared by changing reactive conditions in this reverse microemulsion.The powders are characterized by SEM, TG-DSC and XRD measurements. The main conclusions in this article are as follows:(1) The content of surfactant CTAB has an obvious effect on the stability of the reverse microemulsion through the comparison of the maximum volume of solubilizing water in different water-in-oil microemulsion systems. When the concentration of surfactant CTAB is less than 0.6mol/L in oil phase of cyclohexane, not only the numbers of reverse micelles but also aggregation of each micelle all increase along with the increase of the concentration of surfactant CTAB, so the maximum volume of solubilizing water is enlarged and stability of the water-in-oil microemulsion system is strengthened. When the concentration of surfactant CTAB is more than 0.6mol/L,because the concentration of surfactant CTAB is not change any more, the maximum volume of solubilizing water in water-in-oil microemulsion systems is not variable. Otherwise, over many carbon hydrogen links of CTAB interwind, this brings about the falling of the stability of the reverse microemulsion.(2) In the CTAB/n-butanol/cyclohexane/water microemulsion system, the content of cosurfactant n-butanol has a great effect on the interfacial film of the reverse microemulsion. When the concentration of cosurfactant n-butanol is 3.5mol/L in oil phase of cyclohexane and the interfacial film is more intensive, so the microemulsion is more stable. But the concentration of cosurfactant n-butanol has little effect on the maximum volume of solubilizing water. The content of cosurfactant n-butanol is more than or less than 3.5mol/L, the stability of reverse microemulsion will fall.(3) When using aluminum nitrate (ammonia liquor) instead of water phase, we found the maximum volume of solubilizing solution will fall along with the increase of the concentration of electrolyte solution in the CTAB/n-butanol/cyclohexane/water microemulsion system and the volume of solution is less than the volume of de-ionized water. It is because ions compress double electric layer of polar group of surfactant, the stability of reverse microemulsion will fall.(4) The CTAB/n-butanol/cyclohexane/water reverse microemulsion with proper proportion goes through three microstructures successively, when the volume of solubilizing de-ionized water increase. They are water droplets in oil, bicontinuous structure and oil droplets in water. The electrical conductivity presents typical percolation filtration phenomenon, when the microstructure of microemulsion is water droplets in oil.(5) It is feasible method that using the variation curves of the electrical conductivity judges the microstructure of microemulsion. Proper proportion of the reverse microemulsion is the concentration of surfactant CTAB is 0.6mol/L and the concentration of cosurfactant n-butanol is 3.5mol/L in oil phase of cyclohexane.(6) In the case of reactive conditions maintain unchanging, the grain size of alumina nanoparticles can be controlled by the adjustment of the volume of water. The diameter of water nucleus in reverse microemulsion is relative toωvalue, and it also restricts the growth of nanoparticles. According toω=[water]/[surfant],the particle size of nanoparticles can be controlled by the adjustment of the volume of water. The result shows that the diameter of alumina D_ω1, D_ω2(D₂) and D_ω3 is 30nm, 40nm and 80nm, whenω₁:ω₂:ω3=1:2:3. The diameter of alumina nanoparticles increase along withωvalue. The strength of interfacial film go worse, water nucleus go distorted and broken, so the ability of controlling the size of nanoparticles will weaken, when the volume of water is too much. These factors results in the growth of the particle size and the worse of dispersity.(7) In the case of reactive conditions maintain unchanging, the grain size of alumina nanoparticles will grow along with the increase of concentration of reactant. The results show that the particle size of alumina nanoparticles is 25nm, 40nm and 50nm, when the concentration of aluminum nitrate solution is 0.1 mol/L, 0.5mol/L and 1 mol/L.But the stability of microemulsion will reduce, when the concentration of reactant is too much. The dispersity of nanoparticles will fall.(8) Alumina nanoparticles are characterized by SEM, TG-DSC and XRD measurements. The precursor of alumina becameα- Al-2O-3 at 1150°C completely by double-microemulsion method. Compared with 1200°C in conventional method, it is lower. The size distribution of the powders is homogeneous and the dispersity is good.