In view of these results,strikingly different behavior is observed for surfactant covered particles in nonpolar medium.With
the stabilized dispersions, the adsorbed layer has an appreciable
thickness,hence,the interaction between particles is “soft” in
nature as a result of longer range of interaction,which differs from
the assumption of hard sphere in the established theory of the
viscosity of suspension [29,32]. Furthermore,it seems that the
balance between repulsive and attractive forces between particles
may represent a crucial factor underlying the effect of particles on
the viscosity property of MRFs.