Rheological properties of montmorillonite dispersions in dilute NaCl concentration investigated by ultrasonic spinning rheometry

Rheological changes of gelled montmorillonite dispersions with different NaCl concentrations and alkali conditions were evaluated by ultrasonic spinning rheometry. It uses velocity-profile information that is obtained in an open-cylindrical container under periodic oscillations. The measurement was conducted with a focus on the rheological behavior at a low shear rate O(1 s−1), which is difficult to measure because of shear banding. The rheometry represents the coexistence of gel and sol conditions in dispersions as profiles of the phase lag of oscillations that are propagated from the cylinder wall. The critical shear rate at a yielding point and the onset of shear-thinning behavior was quantified, which has been regarded as only an apparent or speculated value by many previous researchers. Viscoelasticity from particle networks in the dispersion was observed, and the networks deform like a spring, without breaking the structure under low-shear-rate conditions.