Convective instabilities in ferrofluids with internal structures

A. Yu. Zubarev - L. Yu. Iskakova

Ural State University, 620083, Ekaterinburg, Russia}

Abstract
The influence of chain-like microstructures on the thermo- and electroconvective instabilities in ferrofluids is studied theoretically. A thin horizontal flat gap, filled with a ferrofluid and exposed to a horizontal magnetic field, is considered. Analysis shows that due to the chains, the critical, for the instability, vertical gradient of temperature decreases with the magnetic field for the hydrodynamic perturbations, periodical in the direction perpendicular to the applied field, and increases significantly with the field for the perturbations, periodical along the field. A vertical electric field induces an electroconvective instability in ferrofluids. The critical magnitude of the electric field depends on the horizontal magnetic field non monotonically, with minimum. The period of the electrohydrodynamic structures increases when the magnetic field increases. Analysis shows that these electrodynamic instabilities in ferrofluids can appear only due to the anisotropic internal structures (chains), aligned perpendicular to the electric field. In the systems with individual particles only this phenomenon is impossible. Figs 4, Refs 16.