Elastic Properties of Magnetic Fluids

Statistical theory and microscopic expression of the stress tensor in the model of a two-component magnetic fluid have been employed to derive analytical relations for dynamic relaxational volume K-r(omega) and shear mu(omega) elasticity moduli that take into account the contributions of translational and structural relaxation processes. The frequency dispersion of the dynamic elasticity moduli of magnetic fluids has been investigated on the basis of the obtained expressions. It has been shown that, at high frequencies, the volume and shear elasticity moduli cease to depend on the frequency and tend to the values of "solid-like" elasticity moduli K-infinity and mu(infinity). Ratio K-r(omega)/mu(omega) has been calculated in a wide frequency range. The obtained K-r(omega)/mu(omega) values lie in a range corresponding to the predictions of the phenomenological relaxation theory. A numerical calculation has been performed for the dependences of the elasticity moduli of magnetic fluids on the strength of an external magnetic field, and it has been shown that, in accordance with the literature data, the isofrequency volume and shear elasticity moduli increase nonlinearly with the field strength.