The interpretation of rheograms of magnetic lacquers measured with a couette apparatus

Magnetic lacquers show pseudo plastic behaviour with a yieid value. Magnetic lacquers are always flocculated suspensions due to the large magnetic attraction forces between the particles. Flocs are also seen on TEM or SEM micrographs. We postulate viscoelastic deformation of the floes with stress relaxation, described by: . If this holds, the measured rheograms could be described with , where and t are parameters to be fitted. The fit of this formula on the measured rheograms is very good indeed. Results of the interpretation of the rheograms as a function of the dispersion time are discussed. The viscoelastic behaviour of flocs was demonstrated elsewhefe by observing the flocs through a microscope in an alternating magnetic field.