Thixotropy is a function of time and shear rate,which refers to
the reversible time-dependence change of viscosity. The MRF
samples were suddenly subjected to a constant high shear rate,
after which the viscosity was followed as a function of time
whereby the structure broke down and an equilibrium value was
reached, then as quickly as possible the shear rate was changed to
the original value.The typical response to such a step-wise change
from one steady-state to another was employed to evaluate the
rebuilding of the structure of MRFs containing surfactants. The
step change test results for MRFs containing 2 wt% surfactants are
shown in Fig. 5(a). It is clear that an abrupt decrease of viscosity
appears in the high shear step, especially for the bare iron based
suspension, as a result of tearing apart of particles and a spatial
arrangement to follow the applied flow field.