Study Of Preparation Of Oleate Sodium Coated Fe₃O₄ Magnetic Fluid And The Surface Structure Of Coated Layer

Magnetic Fluid (MF) is a stability colloid which is composed of magnetic particles, surfactant and based liquid. MF has many special qualities which other solid materials and liquid materials don't have, such as solid's magnetism and liquid's fluidity. MF is also a stable colloid under gravity and magnetic field. It can be extensive used in the filed of seal, polishing, target drug deliver, hyperthermia and so on. But the problem of MF with low stability has not been solved well, limiting the extensive application. To solve this problem, we systemic studied how the method of preparation, surfactant, and the surface structure of coated layer influenced the stability of MF. At last, we primary investigated the preparation of the magnetic nano-microspheres with target drug deliver. The paper drew some original results as follows.The results show that the optimal reaction temperature is 75°C and the optimal concentration is 0.5mol/L.The temperature mainly influenced the crystal and then the magnetism in the conventional coprecipitation method, while the concentration mainly influenced on growth speed of magnetic particles and then on the diameter of magnetic particles.The optimal pH value when coated by oleate sodium was 5.5. While the optimal pH value for oleate coated magnetic fluid dispersing into water was 10. There was a chemical adsorbed between the magnetic particles and oleate sodium which decreased the surface tension and increased the resistance, so the stability of MF improved obviously. The magnetization of coated magnetic particles was lower than the uncoated ones, and this reduction is likely due to the existence of disordered spins at the surface as discussed.We characterized the structure of oleate coated MF layer: the oleate sodium was chemical adsorbed on the surface of particle to form the primary layer while the excess oleate sodim was physical adsorbed on the first layer to form second layer. We concluded the key condition to prepare MF with the stable structure was a drive which can make the surfactant close to the surface of magnetic particles and the surfactant was firmly adsorbed on the surface of particles. We found that the magnetic nanoparticles prepared by co-precipitation had extensive hydroxyl groups on the surface. And the H+ would adsorb on these hydroxyl groups under acidic environment. When added oleate sodium into solution, the electrostatic interaction between their carboxylic acid head groups and the hydroxyl groups will make them combine tougher. Consequently, the iron oxide particles were coated by a well-organized primary oleic acid radical molecule. Then, the excess oleate sodim was weakly adsorbed on the primary layer of the oleate sodium-coated magnetic particles to form a hydrophobic shell through the hydrophobic interaction between the subsequent molecule and the hydrophobic tail of oleate of the primary layer. So the second layer will be easily washed by acetone or alcohol. The magnetic particles coated by oleate sodium can disperse into polar or unpolar solution.MF can be used as target drug deliver...