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Nanofluids are the two-phase systems in which solid nanoparticles are dispersed in a very small amount in conventional base fluid, mostly water and oils but also other common solvents. Well-designed and carefully optimized, nanofluids show a number of advantages over conventional suspensions in various fields of application – as heat transfer fluids, transformer oils, etc. Here, very important issues are their good dispersibility and long-term stability. According to DVLO - Derjaguin, Verway, Landau & Overbeek theory on the stability of the colloidal solutions, the basic precondition for obtaining the stability is the dominance of the repulsive forces between the dispersed particles. There are two kinds of repulsion within the fundamental mechanism ; one is steric repulsion, and another is electrostatic repulsion. For achieving the steric stabilization, specially designed polymer molecules with the ability to absorb on the surface of the particles that contribute to the additional increase of the steric repulsive forces are looked for. In this work, results of preparation of stable nanostructured fluids and some of its properties like thermal conductivity will be presented and discussed. As solid phase, metal oxide nanoparticles and multiwalled carbon nanotubes were used ; base fluids were mineral transformer oil, as well as mineral, synthetic and biodegradable lubricating base oils. In order to achieve stability of the two-phase system, efficiency of the several types of commercially available surfactant as well as dispersant copolymers based on styrene-methacrylate monomers designed in our laboratory were tested. |
