Uniform dispersion of fine particles in a magnetic fluid and its evaluation

Particles confined in a thin horizontal layer of magnetic fluid were uniformly dispersed by applying a vertical magnetic field. The particle arrangements were observed both in experiments and in two-dimensional computer simulations. The regularity of particle dispersion was defined by the mean value of areas of the Voronoi polygons and its variance, R = 〈a〉 2/σ 2, for the evaluation of the particle arrangements. The clusters of particles were virtually produced by uniformly swelling all of the particles. The distribution of the cluster size can be utilized for detailed evaluation of the particle arrangements The regularity of the particle dispersion depends on the repulsive force acting between the particles. The uniformity of particle dispersion increases with the intensity of the magnetic field and the initial concentration of the particles.