Journal of Rheology, Vol.45, No.5, 1193-1203, 2001
Thermorheological behavior of magnetic dispersions
We examine the temperature dependence of the steady and oscillatory shear flow properties of magnetic dispersions. The dispersions-characteristic of those used in the production of flexible magnetic data storage media-consist of acicular ferromagnetic metal oxide particles suspended in a solution of low molecular weight polymer and organic solvent. Although the viscosity of the suspending fluid is independent of shear rate and displays traditional temperature dependence, the viscosity of the dispersion is dramatically shear thinning and effectively independent of temperature, The small-amplitude oscillatory shear flow material functions are also nearly independent of temperature. By examining dispersions wherein part of the magnetic particles are replaced with nonmagnetic-but otherwise identical-particles we confirm that the temperature independence is a consequence of the rheological behavior being governed by temperature-independent interparticle magnetic forces.