Nucleation Theory of Structure Evolution in Magnetorheological Fluid

A phenomenological model of nucleation-controlled structure evolution in dilute magnetorheological (MR) fluid is suggested. We find that the critical diameter of column nuclei is related to the external magnetic field Ho, the increase in permeability Att of the nuclei, and to the nucleus surface tension a, by a relation of the form D, = 2a/[JAg I + (I /87r)(H' -H2)(A/t/lI)]. The growth rate of columnar structure, and the field and volume fraction dependencies of the separation between the columns are calculated, and found to be given respectively by d -t d -H ³ 1 ⁴ , and d - 1/7. These results fit the experimental data in ferrofluid emulsion systems very well.