We describe in this section the non-Newtonian complex behav- ior shown by Aerosil R816 ® PPG400 suspensions. This fluid has been characterized in Section 2, and it presents a shear-thickening region between two shear-thinning regions in the flow curve. We have conducted a set of experiments in the adapted rheometer to obtain the velocity profiles shown in Fig. 9. One must observe that the flow is nearly unidirectional, so the radial velocity is almost zero in all the cases. On the other hand, the non-dimensional az- imuthal velocity profile is always beneath the theoretical Newto- nian profile as one can expect for a shear-thinning liquid for small rotation rates. If one increases the rotation rate, the velocity pro- file near the inner cylinder reduces its slope, until it reaches al- most the Newtonian profile for = 30 rpm and ξ < 1.2. Increas- ing even more the rotation rate, the velocity profile agrees with the Newtonian one for ξ < 1.4 and = 50 rpm. For the highest rotation rate ( = 75 rpm), the velocity profile has a slope lower than the Newtonian one except for the area near the outer radius (ξ AR). This can be explained by the fact that the greater the rotation rate, the greater the shear-rate near the surface is, and thus leading to higher values of the viscosity due to the charac- teristic of the steady viscosity curve. This similar behavior was re- ported before in [14]. The fluids used in this latter study exhibit two external shear-thinning regions with strong slopes and differ- ent radial regions were characterized depending on the shear-rate. In our case, we make a novel key observation between the shear- thickening and shear-thinning regions in terms of the radial veloc- ity profiles: there is a transition in the trend of the azimuthal ve- locity. The shape of the profile near the vicinity of the inner cylin- der varies smoothly from values lower to greater than those given for a Newtonian fluid.