Macroscopic Structure Change and Optical Anisotropy Induced by Yield Behavior of Clay Dispersing Colloidal Gels

The relationship between the yield like behaviors and macroscopic and microscopic structures of the colloidal gels, which are consisted by silicone oil, hectorite and PEO, are examined from the rheological property, the anisotropic optical property and the flow behavior. These colloidal gels exhibit the yield behaviors in the stress ramp test and another yield like behavior is also observed in the high shear regime. From the motion of the oil droplets observed by the high-speed microscope and result of the flow birefringence measurements, the occurrence of the first yield behavior would be caused by generation of the thin shear layer and the other layers do not change their macroscopic structure for a while. During the flow after the first yield behavior, some part of the sample in the flow field becomes viscous thickening suddenly and it causes a large-scale flow fluctuation. The high viscosity region spreads to a whole area and a whoop stress appears. In this state, the flow birefringence shows the similar behavior of the polymer fluids. Therefore, we thought that the macroscopic structure related to the second yield behavior includes the entanglement like polymer fluids.