The microstructure of ferrofluids and their rheological properties

Abstract

One of the most important features of ferrofluids is the possibility to change their physical properties, especially their viscosity, by means of moderate magnetic fields. This capability makes ferrofluids very useful in the fields of engineering, medicine and fundamental research. Rheological experimental results, as well as theoretical studies, correlate the change of the viscosity of a sheared ferrofluid under the influence of a magnetic field, the so-called magnetoviscous effect, to the internal structure formation under certain external conditions. To obtain information about the microstructure of ferrofluids, experiments using the small-angle neutron scattering (SANS) technique have been carried out. Three magnetite-based ferrofluids with different particle-particle interactions, and thus various magnitudes of the magnetoviscous effect, were investigated. Using a specially designed rheometer, SANS experiments were performed for different shear rates and magnetic field strengths in order to observe the modification of the microstructure in ferrofluids and to associate the SANS information with their macroscopical behaviour. The scattering patterns obtained show a good agreement with the qualitative model that explains the magnetoviscous effect.

Preparation and rheological studies of uncoated and PVA-coated magnetite nanofluid

“…However, at constant shear rate the viscosity increases with increase in the magnetic field (Fig. 4) until it reaches a saturation point which is in agreement with the Pop et al findings [42]. For FF, the viscosity is determined by the viscosity of carrier liquid (water) and the interaction of MNPs.…”

Microstructure and rheology of ferrofluids

“…4e and f). The agreement with the qualitative model developed to explain the macroscopical behaviour of ferrofluids [9] is confirmed also by the scattering curves obtained for Co ferrofluids. The radial averaged intensity plotted as a function of the scattering vector (Q) shows no dependence on the shear rate for the situation without magnetic field (see Fig.…”

Structure and magnetic properties of mono- and bi-dispersed ferrofluids as revealed by simulations

“…Also, it is found that SðK xz Þ increases in the high-K xz region as the magnetic field increases. Our results can be used to interpret experimental observations as obtained in a recent work [19] on the anisotropic structure of colloidal ferrofluids.…”