Two-body interaction in the rigid dipole suspension under the effect of the rotating field

The behavior of a pair of spherical particles-rigid magnetic dipoles-under the effect of a rotating field was studied. The particle motion in the plan e of field rotation was considered taking into account the hydrodynamic and dipole-dipole interactions of the particles. It is shown that, because of an abrupt increase in viscous friction near the contact of ideally smooth s pherical particles rigid doublets are formed, whereas the behavior of real particles is very sensitive to the state of their surface, which was taken into consideration through the introduction of a minimal clearance. In weak fields, particles are bound together by the virtue of the orientational di pole interaction and rotate synchronously as an entity up to some critical frequency. In the asynchronous region, beginning with a certain field stren gth, a new motion mode comes into being: the orientational bond between par ticles is disrupted; the mean velocity of individual particle rotation is c lose to the velocity of field rotation; and, owing to hydrodynamic interact ion between rotating particles, the rotation velocity for the pair of parti cles varies linearly with the field frequency and depends on the state of t he particle surface. Particular conclusions of the theory are supported by results of our own experiments.