Rotational-type viscometers are the most representative methodology in the rheometry, and commonly used in flow curve measurement, creep test, and dynamic viscoelastic spectroscopy. From the view point of measurement accuracy, however is some cases, the rotational-types are inferior to the capillary-types especially in measuring less viscosity than 1 mPa·s. Recently, the authors developed a series of viscosity measurement systems based on the electromagnetically spinning (EMS) method, which can provide both the rotational-type's versatility and the capillary-type's accuracy. In addition, these EMS systems have advantages of a perfectly sealed condition as well as a disposable usage so that they will break new ground for rheometry. In this paper, we introduced the noteworthy features of each of the EMS series, and showed some interesting results by rheometry in lowly viscous fluids.
A measurement technique for the first normal stress difference using a conventional rheometer with a concentric cylinder flow cell is examined. The conventional rheometer, which can control the up and down speeds of an inner cylinder of the concentric cylinder flow cell and can also measure the thrust force, is used in this technique. The other additional instruments or the optional devices are not required. The inner cylinder is pushed down with a constant velocity into the sample filled in the cup. The resistant force acting on the inner cylinder is measured during this motion. The resistant force is caused by the buoyancy, the shear stress acting on the side surface of the inner cylinder and the pressure acting on the top and bottom of the inner cylinder. The buoyancy and the shear stress can be calculated based on the shape of the inner cylinder and the moving velocity. If the inlet and outlet pressure drop can be ignored, the pressure caused by the first normal stress difference can be evaluated from the thrust force and the shear viscosity.
The yield behavior and the shear layer formation during the shear flow of gels were investigated using a twin-drive rheometer, which is equipped with two driving and measuring systems. The stress-ramp test was conducted and each stress acting on the upper and lower plates was separately evaluated and compared. As a result, it was found that the stress on the fixed side plate significantly shifts from the others when the yield behavior occurs. When the stress increase rate in the stress sweep test is sufficiently low, the stress difference is eliminated after the yield and the same stresses are obtained on both plates, however, when the stress increase rate is high, the stress difference continues to occur during the test. These results demonstrated the generation of a thin shear layer at and after the yield behavior and it exists until the end of the stress-ramp test because of its non-equilibrium stress condition.
The new rheometrical techniques are demonstrated to examine the yield behavior for α-gels. The yield behaviors and re-structuring process are observed by using the repeated stress ramp test and the stress relaxation experiment after the stress ramp test. In this specific test, continuously change from the stress control mode to the strain control mode, a newly developed high performance rheometer is used. The first yield behavior is strongly affected by the hysterical effect. The first yield stress is recovered during a certain interval time. Furthermore, when the interval time is longer, the first yield stress is increased gradually. The second yield stress is hardly affected by the hysterical effect. The relaxation process shows very complex behavior. This behavior is organized by the three mode Maxwell Model. The experimental results are in good agreement with the three mode Maxwell model. The first one of three Maxwell elements shows the short time relaxation time that is corresponding to the viscous nature generated by the first yield behavior. The second element is related with the second yield behavior and it exhibits the negative stress. The last element shows the long relaxation time that is corresponding to the first yield behavior and re-structuring behavior.
A technique to evaluate transiently the orientation director of liquid crystal on the surface of thin liquid film using by measuring the anisotropic reflection of S-polar and P-polar at incidence angle which is near Brewster's angle is developed. The high-speed rotary half-wave plate type polarized state generator, which rotates the light polarized direction with a constant speed, is applied on the prove light. The modulated laser beam is irradiated on the surface at a certain incident angle, and the light intensity of the reflection beam is measured. The maximum and minimum values of each period of the measured light intensity shows the reflected light intensity of the S- and P-polarized light, respectively. The Brewster's angle of orientation film depends on azimuth angle between the orientation direction and the plane of incidence, because Brewster's angle is decided by the refractive index and these films have the birefringence. The phase changing process from the nematic to the cholesteric phase on the coating film of a Hydroxypropylcellulose 50 wt% aqueous solution during drying was evaluated by measuring dependence of Brewster's angle on the azimuth angle. The result shows a good agreement with the birefringence and dichroism evaluated by the transmitted light.
Polarization imaging method, PIM, can provide us with two-dimensionally spatial distributions of birefringence and extinction angle. In a previous study, we reported a new rheo-optical apparatus based on conbination of PIM and a conventional rheometer. The appratus was very effective to visualize the stress field of shear induced sturucture. However, there was a problem in the quantitative evaluation of birefringence, which can be attributed to non-ideality of the wave plate for the circuler polarizer. In this paper, we improved the wave plate and reports a new data for a wormlike micelle solution which is composed of 30 mol/m3 cetyltrimethylammonium bromide and 60 mol/m3 sodium salicylate. While the previous optical system provided us with 2-fold symmetry images, the new one provided us with almost uniform birefringence distributions. The spatially mean value of the birefringence distribution, [Δn], in low strain range in the new optical system meets the stress-optical rule, and the stress-optical coefficient is consistent to literature value in linear regime. In non-linear regime where the finite extensibility effect significantly contribute to the stress, the stress-optical coefficient can be described as a unique function of orientation factor of micelles.
We previously investigated anomalous phenomena in pressure drops of (drag-reducing) rod-like micelle surfactant solutions passing small apertures. Compared with water results, pressure drops of rod-like micelle surfactant solutions rose steeply at any Reynolds number. The anomalous pressure drops was dependence of molar concentration ratio, which was relationship between molar concentration of cationic surfactant solution and those of counter ion. For only the ratio = 1.0, anomaly of pressure drops was obtained. However, the mechanism was not clear for using only 1 surfactant solution and discussing non-Newtonian viscosity. In this situation, pressure drop was measured with constant flow rate because of investigating flow properties of 2 types of rod-like micelle surfactant solutions passing through small apertures with inner diameter (characteristic length) ranging 100 μm to 1000 μm (= 1.0 mm). The resultant pressure drops of water agreed with the predictions and previous ones passing through small apertures. The flow properties of rod-like micelle surfactant solution which was used in our previous study were similar to previous ones. However, pressure drops of another rod-like micelle surfactant solution were different and increased invariably. We measured storage modulus and loss modulus of the used rod-like micelle surfactant solutions and estimated relaxation time for discussing elastic properties. For plotting dimensionless pressure drops against Weissenberg number (Wi), it found that anomalous pressure drops of rod-like micelle surfactant solutions appeared in Wi > 100. We discussed thus that the phenomena were caused by elasticity.