To the theory of rheological properties of ferrofluids: influence of drop-like aggregates

Many experiments show that drop-like aggregates, consisting of tremendous number of magnetic particles, can appear in ferrofluids under suitable conditions. Our work deals with theoretical study of influence of these drops on macroscopical rheological properties of the systems. The estimates show that appearance of the drops leads to significant (more than order of magnitude) increase of viscosity of ferrofluid under magnetic field parallel to gradient of flow. This conclusion is in agreement with known experimental results. Our analysis is performed for a model monodisperse system of magnetic particles suspended in a Newtonian fluid. The influence of polydispersity, the general and inevitable property of ferrofluids, on the magnetoviscous effects in these systems is discussed.