The flow characteristics of angel O/W emulsion, which is a yield stress fluid, was investigated. The hysteresis loop test was conducted for the strain below the slip yield point, and the single relaxation Maxwell model was used to fit the experimental data. Using these methods, the shear-rate dependence, stress dependence, and time dependence of the viscoelastic properties of the sample were evaluated in the region below the slip yield point. The shear-rate dependence induced by the stress-ramp rate and the stress dependence from the maximum applied stress influence the viscoelastic characteristics below the slip yield point in terms of the flow history. However, the time dependence of the viscoelastic characteristics could not be confirmed for any creep time. The yield stress measured in the stress-ramp test increases with the stress-ramp rate owing to the contribution of the viscous strain from the flow history.

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In fiber suspensions, fibers with three-dimensional orientation states are dramatically flow oriented in the flow-flow gradient plane when the flow starts. In contrast, large strains are required for flow orientation in the flow-vorticity plane. Under oscillatory shear flow, when the strain amplitude is small, the flow orientation in the flow-vorticity plane is weakly induced, unlike that in the flow-flow gradient plane. The orientation in the flow-vorticity plane increases with the strain amplitude. At large strain amplitudes, fibers are oriented in the flow-flow gradient plane; thus, the rotational motion of fibers in the flow-flow gradient plane is dominant, i.e., fibers are almost flow oriented in the flow-vorticity plane. However, contributions of the oscillatory behavior of fiber orientation in the flow-flow gradient and flow-vorticity planes to complex viscosity are unclear. Herein, we adjusted the two initial orientation states (random and flow-oriented states) for the strain sweep test to determine the contributions of fiber orientation in each plane to complex viscosity. Furthermore, phase transition behaviors from the random to flow-oriented state in the flow-vorticity plane with increasing strain amplitude were qualitatively estimated as the orientation angle via visualization. Consequently, when the initial orientation was random, the fibers gradually vibrated in a medium strain amplitude region and complex viscosity was higher than that of the initial flow-oriented state. We divided the complex viscosity behavior of the strain sweep test into five strain amplitude regions and clarified the dominant orientation state in each region.

In this study, we investigated the influence of compatibility between the particle and the dispersant on the rheological property using condensed suspensions with different dispersants (epoxy or amine). In the general flow-curve, the samples have not difference. In the solid regime below the yield stress, the amine-based sample with good compatibility has the flow history as the increases of viscosity in the decrease segment on the hysteresis loop test. In the fluid regime of middle strain range, the thickening and hardening happens at the time of the reversal rotation on the amine-based sample. It is found that the good compatibility influences the wide strain range from the solid regime to the fluid regime as the flow history.

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