Particle-interaction effects in the flow of a ferroliquid in a magnetic field

E. E. Bibik

Abstract
Magnetic dipole-dipole interaction of particles in ferroliquids results in the formation of clusters even when there is no field and also produces change in an external field or parallel layers in a rotating field. The condition for conservation of the macroscopic uniformity of the liquid is the smallness of the dipole interaction relative to the thermal energy of the particles, and this implies that the maximum attainable saturation magnetization of the liquid is not dependent on the choice of magnetic material. The formation of chains increases the energy dissipation when the liquid flows in a direction perpendicular to the external field. When the velocity gradient is of the order of 10⁻⁵ sec⁻¹ and also when it is large (10³ sec⁻¹), the shear resistance is proportional to the gradient, and in the first case the viscosity is higher by orders of magnitude than that in the second. At intermediate gradients, the shear resistance due to chain formation is not dependent on the velocity gradient. The formation of the chains increases the magnetic susceptibility and the attenuation coefficient for light passing through the liquid. Clustering reduces the initial magnetic permeability. In a flow, the chains or clusters are broken up, so these effects are reduced. A theory is given for these effects, together with some results from an experimental study. It is found that the effects are markedly dependent on the surface interaction forces of the particles.