Thermodynamic Discussions for Constitutive Equations of Magnetic Fluids with Viscoelastic Effect (Polar Fluid Theory)

The strong interaction of colloidal ferromagnetic particles dispersed in nonconducting mother liquors shows extraordinary magneto-optical phenomena and non-Newtonian flow characteristics. In this case, a term caused by the strain energy must be added into the constitutive equation of stress in magnetic fluids. In the present paper, a new constitutive equation of magnetic fluids with viscoelastic effect are formulated by the thermodynamic method wherein free energy and dissipation function are used on the basis of kinematical balance equations in the polar fluid theory. As a result, not only an interaction term due to internal rotation but also an elastic interaction term are introduced into the system of the equations. And by use of a constitutive equation of magnetization determined here, we can show that an anisotropy of magnetic permability due to a polar effect causes an anisotropy of the refractive index of light in magnetic fluids.