Preparation And Rheological Characterization Of Magnetic Fluids

In the treatise, the preparation techniques of magnetic fluids (MFs) in different solvents, like water, toluene, etc. were studied, and rheological behaviors of MFs, dispersibility and stability were investigated experimentally by several instruments, such as IR, XRD, SEM, TEM, VSM, Gouy magnetic balance, capillary rheometer and rotating rheometer. The relationship between rheological characteristics and the influential factors, such as carrier fluid properties, solid content, the properties and dosage of surfactant, temperature and intensity of magnetic field, etc., were discussed, so experimental data and derived theoretical results would be valuable reference for future research of MF.The following were described in detail:1. A capillary rheometer designed to study the rheological behaviors of MF experimentally was set up, and according to the basic principles of capillary rheometry, suitable measurement devices and procedures were designed, so the equipment constant was determined properly. Under the same flow rate, by measuring the pressure difference of pure water or glycerine-aqueous solution through the different capillary tubes with equal diameter but none equal length, the side effects and kinetic energy loss could be avoided completely, and the equipment constant of capillary rheometer could be determined properly. Comparing with the viscosity of standard samples, the accuracy of the data measured by designed capillary rheometer was excellent, so the capillary rheometer provided a satisfied investigation tools for rheological properties of MF.2. The rheological behaviors of MF were studied experimentally, especially, the viscosities of different MFs were measured, and the relation between the viscosities of MFs and several key factors, such as the particle size and size distribution, solid content, particle aggregation, the kinds and dosage of additive, were discussed. The rheological properties of several low solid content MFs were compared by experiments. It was found that low solid content MF is a kind of Newtonian fluid, the MF keeps the Newtonian behavior even under external magnetic field. Based on Einstein viscosity formula and taken account of all influential factors, a more effective theoretical formula on viscosity of MF was derived. The viscosities of several kinds of MF prepared were calculated by the new formula, and compared with experimental data, it was found that the new formula is more accurate than the Einstein viscosity formula, and can be used to predict the viscosity of low solid content MF properly.3. Several kinds of water-based Fe₃O₄ MF with different solid contents were prepared by mechanical agitation (MA) or high-energy ball milling (HEBM), respectively, and their rheological characters were studied. For MFs prepared by MA with low solid content, the relationship between viscosity and preparation conditions, the dosage of surfactants, temperature, and the effects of magnetic field were investigated by the capillary rheometer. It was found that these kinds of MFs are fit to the conditions of Newtonian fluid quite well. For high solid content MF prepared by HEBM, the relationship of rheological properties and shear-thinning behavior, thixotropy, constitutive equation, and the effects of magnetic field were studied, and it could be found that these kinds of MFs are non-Newtonian and can be predicted by H-B formula.4. Several kinds of toluene-based Fe₃O₄ MFs were prepared, and their rheological properties were studied. Magnetic Fe₃O₄ nanoparticles were synthesized by chemical coprecipitation, and then were surface-modified with oleate sodium to obtain toluene-based Fe₃O₄ MF. The prepared MF could be characterized by several instruments, such as IR, XRD, SEM, TEM, VSM, laser particle size analyzer, UV-visible spectrophotometer, Gouy magnetic balance, rheometer, etc. It could be found that the particle in MF has small size, and also has excellent dispersibility and stability. By mixing the MF with PMMA, a PMMA magnetic film was prepared, it was found by tensile experiment that the toughness of PMMA film can be improved obviously.