Role of nucleation in the structure evolution of a magnetorheological fluid

A phenomenological model of nucleation-controlled structure evolution in dilute magnetorheological fluid is suggested. We find that the critical size of column nuclei is related to the magnetic field H, the increase of permeability delta mu of the nuclei, and to the nucleus surface tension a, by the relation D-c similar to 16 pi sigma/(H-2-H-c(2))delta mu. The growth rate of columnar structure,and the field and volume fraction dependences of the separation between the columns are calculated, and are found to be given, respectively, by d similar to t(2/7), d similar to H-3/14, and d similar to phi(1/7). These results fit the experimental data in ferrofluid emulsion systems very well.