Therefore, the measurement result recorded are calculated as (2) where M d is the actually measured torque acting on the rotor, M is the torque used to calculate the viscosity of the sample, taking into account the effect of friction

characteristic of the measurement geometry. The described selleck procedure can be carried out only for the rotational measurement. In the case of oscillatory measurements, it does not work; so, in using the pressure chamber or electrorheological system, it is not possible to determine the viscoelastic properties of the material. After the calibration of the pressure chamber, its position should not be altered. The pressure chamber was filled with the hand pump. By using the automatic measuring pipette, the sample was filled with carefully into the cylinder of the hand pump. After that, the sample was pumped into the measuring chamber. These activities were repeated until the complete filling of the measuring system. The volume of the sample during the measurements was 120 cm3. To increase the pressure in the measuring cell, the hand pump also

was used. The pressure in the experimental system was raised to the value of 7.5 MPa. Before the start of the measuring series, we checked the measuring range of PZ38 cylindrical geometry. The lower measuring range is limited to two parameters: the lowest permitted torque acting on the Selleck AP24534 rotor (a) at a low shear rate is 250 μNm, measuring points collected at lower values of torque may be considered as burdened with Thymidine kinase too much uncertainty and can be rejected and (b) at high shear rates and for materials

with low viscosity, the Taylor vortices can be formed, which disturbs the laminar flow in the measuring chamber. Based on theoretical considerations, Taylor [64] predicted that when the inner cylinder is rotating, there should be a certain critical frequency of rotation above which, in the flowing fluid, creates a series of regular vortices that fill the annular gap between the cylinders. Taylor not only calculated the critical frequency of the rotation, but also experimentally proved the existence of vortices. Characteristically, spiral Taylor vortices proceed the transition to turbulent motion. The axes of the vortices formed in sections of the annular gap are parallel to the primordial direction of fluid flow. For these reasons, it is important that the shear rate range during the calibration of friction corresponded to the measuring range of the test sample with a defined viscosity. The rotation measurements under the pressure of 7.5 MPa were performed at the shear rate range from 0.01 to 1,000 s −1 in the logarithmic scale.