Linear viscoelasticity of an inverse ferrofluid

A magnetorheological fluid consisting of colloidal silica spheres suspended in an organic ferrofluid is described. Its linear viscoelastic behavior as a function of frequency, magnetic field strength, and silica volume fracti on was investigated with a specially designed magnetorheometer. The storage modulus G' is at least an order of magnitude larger than the loss modulus G " at all magnetic held strengths investigated, G' does depend only weakly on frequency, and linearly on volume fraction. A model is presented for th e high frequency limit of the storage modulus G(infinity)'. In the model ou r system is heated as a collection of single noninteracting chains of parti cles. Assuming a dipolar magnetic interaction, theory and experiment show r easonable agreement at high frequencies. [S1063-651X(99)16510-3].